92387738 epri 1000987 mechanical seal maintenance and application guide (2)

Mechanical Seal Maintenance andApplication Guide

Technical Report

LI

CE

NS E D

M A T E

RI

AL

Equipment

Reliability

Plant

Maintenance

SupportReduced

Cost

WARNING:Please read the License Agreementon the back cover before removingthe Wrapping Material.

EPRI Project ManagerM. Pugh

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

Mechanical Seal Maintenance andApplication Guide

1000987

Final Report, November 2000

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I)WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, ORSIMILAR ITEM DISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESSFOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON ORINTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUALPROPERTY, OR (III) THAT THIS DOCUMENT IS SUITABLE TO ANY PARTICULAR USER'SCIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER(INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVEHAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOURSELECTION OR USE OF THIS DOCUMENT OR ANY INFORMATION, APPARATUS, METHOD,PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

Kalsi Engineering, Inc.

ORDERING INFORMATION

Requests for copies of this report should be directed to the EPRI Distribution Center, 207 CogginsDrive, P.O. Box 23205, Pleasant Hill, CA 94523, (800) 313-3774.

Electric Power Research Institute and EPRI are registered service marks of the Electric PowerResearch Institute, Inc. EPRI. ELECTRIFY THE WORLD is a service mark of the Electric PowerResearch Institute, Inc.

Copyright © 2000 Electric Power Research Institute, Inc. All rights reserved.

iii

CITATIONS

This report was produced by

Nuclear Maintenance Application CenterEPRI1300 W.T. Harris BoulevardCharlotte, NC 28262

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Mechanical Seal Maintenance and Application Guide, EPRI, Palo Alto, CA: 2000. 1000987.

v

REPORT SUMMARY

This guide provides information to personnel involved with the maintenance of mechanical seals,including good maintenance practices, planning, predictive and preventive techniques, andtroubleshooting guidance. It provides insight to experienced personnel as well as basicinformation, guidance, and instructions to personnel assigned to maintain mechanical seals.

BackgroundA mechanical seal prevents leakage of pressurized fluid between a rotating shaft and a stationaryhousing. They are widely used for numerous power plant equipment applications, particularly onpumps of various sizes and pressure ratings. Even though they are capable of providing long-term service, mechanical seals sometimes exhibit unsatisfactory performance, unpredictablefailures, and a short life, which can directly affect plant reliability and performance, resulting incostly downtime and outages. Mechanical seal issues rank high in surveys completed by powerplant maintenance personnel.

Objectivesx To help power plant personnel deal with the maintenance and reliability issues of this critical

power plant component

x To provide technical information to plant personnel on proper selection and installation ofmechanical seals, seal failure modes, and troubleshooting

x To provide maintenance recommendations for optimizing seal performance and operating life

ApproachA detailed review of industry literature, product information, and standards was conducted toestablish the state of technology for mechanical seals. Utility and industry personnel weresurveyed to determine specific problems and commonly encountered failure mechanisms. Basedon all of the information gathered, suitable recommendations were developed for the problemsencountered and presented in this report.

ResultsThis guide presents a thorough discussion of mechanical seals and provides an in-depthunderstanding of their design and operation, including expected life and a discussion of properapplication and selection. It also provides proper installation methods and guidance on expectedfailure mechanisms. This guide offers troubleshooting approaches to assist in determining thecauses of failure and discusses recommended predictive, preventive, and corrective maintenancepractices. The contents of this guide will assist plant personnel in reducing costs and equipmentunavailability and in improving equipment reliability and performance.

vi

EPRI PerspectiveProblems with mechanical seals represent a significant reliability impact on rotating equipment.This guide provides power plant maintenance personnel with information to help improve sealperformance and component reliability through a better understanding of the operation ofmechanical seals and their critical components. It also provides guidelines on investigating andtroubleshooting problems that arise during inservice operation and normal planned maintenanceactivities.

KeywordsMechanical sealsMaintenanceEngineers

vii

ACKNOWLEDGMENTS

This guide was developed by the Nuclear Maintenance Application Center (NMAC) and thefollowing Technical Advisory Group (TAG):

Steve Lemberger AEP

Bob Mundlapudi Amergen

Vic Varma Consultant

Hugh Nixon Consumers Energy

Steve Rosenau Duke Energy

Larry Price PG&E

Rich Hansen UNICOM

John Montgomery UNICOM

NMAC and the TAG were supported in this effort by:

Kalsi Engineering, Inc.Sugar Land, TX

Principal Investigators:M. S. KalsiP. D. Alvarez

EPRI Licensed Material

ix

CONTENTS

1 INTRODUCTION.................................................................................................................. 1-1

1.1 Background............................................................................................................... 1-1

1.2 Purpose .................................................................................................................... 1-2

1.3 Approach................................................................................................................... 1-2

1.4 Highlighting of Key Points ......................................................................................... 1-3

2 GLOSSARY OF TERMS...................................................................................................... 2-1

3 TECHNICAL DESCRIPTION ............................................................................................... 3-1

3.1 Operating Principles and Basic Components of a Mechanical Face Seal .................. 3-1

3.2 Major Design Variations ............................................................................................ 3-8

3.3 Multiple Seals.......................................................................................................... 3-10

3.4 Seal Cartridges ....................................................................................................... 3-12

3.5 Seal Chamber Design and Flushing ........................................................................ 3-15

3.5.1 Seal Arrangements for Abrasive Applications ..................................................... 3-17

3.6 Closing Force.......................................................................................................... 3-17

3.6.1 Balance Ratio ..................................................................................................... 3-18

3.6.2 Pressure Distribution Between the Sealing Faces .............................................. 3-21

3.6.3 Stationary Versus Rotating Seal Balance ........................................................... 3-22

3.7 Pressure Velocity (PV) Parameter and Limit ........................................................... 3-23

3.8 Temperature Considerations and 'T Limit .............................................................. 3-24

3.9 Improved Seal Face Designs .................................................................................. 3-25

3.10 Hydrostatic Seal Design .......................................................................................... 3-28

4 FAILURE MODES AND FUNDAMENTAL MECHANISMS.................................................. 4-1

4.1 Introduction ............................................................................................................... 4-1

4.2 Definition of Seal Failure ........................................................................................... 4-1

4.3 Industry Survey ......................................................................................................... 4-2

4.4 Fundamental Failure Mechanisms............................................................................. 4-3


x

4.4.1 PV Limits Exceeded ............................................................................................. 4-4

4.4.2 'T Limits Exceeded, Causing Film Vaporization/Collapse .................................... 4-5

4.4.3 Inadequate Cooling .............................................................................................. 4-6

4.4.4 Transients Causing Excessive Seal Face Coning................................................. 4-6

4.4.5 Operation Away from Best Efficiency Point........................................................... 4-9

4.4.6 Seal Misalignment/Premature Degradation of Primary and Secondary Seals ..... 4-12

4.4.7 Excessive Out-of-Flatness (Warpage) During Operation .................................... 4-15

4.4.8 Seal Faces Too Perfectly Flat to Generate a Film............................................... 4-16

5 APPLICATION AND SELECTION RECOMMENDATIONS ................................................. 5-1

5.1 Introduction ............................................................................................................... 5-1

5.2 Selection Specification .............................................................................................. 5-1

5.3 Selection Data Sheet ................................................................................................ 5-3

5.4 Qualification Testing.................................................................................................. 5-6

6 CONDITION-BASED MONITORING GUIDELINES............................................................. 6-1

6.1 Introduction ............................................................................................................... 6-1

6.2 Typical Performance Data Logging ........................................................................... 6-2

6.3 Seal Performance Parameters .................................................................................. 6-5

6.4 Instrumentation ......................................................................................................... 6-5

6.4.1 Temperature Gauge ............................................................................................. 6-5

6.4.2 Thermowells ......................................................................................................... 6-6

6.4.3 Pressure Gauges.................................................................................................. 6-6

6.4.4 Alarm, Trip, and Control Switches ........................................................................ 6-6

6.4.5 Pressure Switches................................................................................................ 6-7

6.4.6 Level Switches ..................................................................................................... 6-7

6.4.7 Level Indicators .................................................................................................... 6-8

6.4.8 Flow Indicators ..................................................................................................... 6-8

7 TROUBLESHOOTING TO IDENTIFY CAUSE OF SEAL FAILURE .................................... 7-1

7.1 Introduction ............................................................................................................... 7-1

7.2 Failure Diagnosis ...................................................................................................... 7-1

7.2.1 External Symptoms of Seal Failure....................................................................... 7-2

7.2.2 Checks Before Dismantling .................................................................................. 7-7

7.2.3 Checks During Dismantling .................................................................................. 7-9

7.2.3.1 General Checks............................................................................................. 7-9


xi

7.2.3.2 Premature Failure Checks........................................................................... 7-10

7.2.3.3 Mid-Life Failure Checks............................................................................... 7-11

7.3 Visual Seal Examination.......................................................................................... 7-12

8 MAINTENANCE................................................................................................................... 8-1

8.1 Introduction ............................................................................................................... 8-1

8.2 Installation and Operation ......................................................................................... 8-2

8.2.1 Seal Handling and Inspection ............................................................................... 8-2

8.2.1.1 Packaging ..................................................................................................... 8-2

8.2.1.2 Storage.......................................................................................................... 8-3

8.2.1.3 Handling ........................................................................................................ 8-3

8.2.1.4 Physical Checks of Mechanical Seals ........................................................... 8-3

8.2.1.5 Seal Rotating and Stationary Components .................................................... 8-3

8.2.1.6 Seal Faces .................................................................................................... 8-4

8.2.1.7 Gaskets......................................................................................................... 8-4

8.2.1.8 Spring............................................................................................................ 8-4

8.2.2 Pre-Installation Equipment Checks....................................................................... 8-4

8.2.2.1 Shaft Straightness ......................................................................................... 8-4

8.2.2.2 Shaft Runout ................................................................................................. 8-5

8.2.2.3 Squareness of Stuffing Box ........................................................................... 8-5

8.2.2.4 Rotational Balance ........................................................................................ 8-6

8.2.2.5 Shaft Bearing Clearances.............................................................................. 8-6

8.2.2.6 Shaft/Sleeve Diameter and Surface Finish .................................................... 8-7

8.2.2.7 Sleeve Hardfacing ......................................................................................... 8-7

8.2.2.8 Sharp Edges ................................................................................................. 8-8

8.2.3 Seal Installation Checks ....................................................................................... 8-8

8.2.3.1 Seal Dimensional Checks.............................................................................. 8-8

8.2.3.2 Seal Cavity Dimensions................................................................................. 8-9

8.2.3.3 Compression Length Tolerance..................................................................... 8-9

8.2.3.4 Auxiliary Glands ............................................................................................ 8-9

8.2.4 Seal Removal ..................................................................................................... 8-10

8.2.4.1 Safety.......................................................................................................... 8-10

8.2.4.2 Failure Evidence.......................................................................................... 8-10

8.2.4.3 Seal Re-use and Inspection......................................................................... 8-10

8.2.5 Startup................................................................................................................ 8-10


xii

8.2.5.1 Avoid Dry Running ...................................................................................... 8-11

8.2.5.2 Filtration ...................................................................................................... 8-11

8.2.5.3 Venting the Stuffing Box .............................................................................. 8-11

9 REFERENCES AND BIBLIOGRAPHY................................................................................ 9-1

A MECHANICAL SEALS APPLICATION AND MAINTENANCE GUIDE SURVEY................A-1

B INSPECTION OF SEAL FACES FOR FLATNESS .............................................................B-1

B.1 Optical Principle ........................................................................................................B-1

B.2 Procedure for Measuring Face Flatness....................................................................B-2

C TRAINING COURSES.........................................................................................................C-1

D LISTING OF KEY INFORMATION ......................................................................................D-1


xiii

LIST OF FIGURES

Figure 3-1 Essential Components of a Mechanical Face Seal................................................. 3-1

Figure 3-2 Multiple Coil Springs .............................................................................................. 3-4

Figure 3-3 Single Coil Springs................................................................................................. 3-4

Figure 3-4 Corrugated Bellows................................................................................................ 3-4

Figure 3-5 Welded Bellows ..................................................................................................... 3-4

Figure 3-6 Rubber Bellows...................................................................................................... 3-5

Figure 3-7 Belleville Washers.................................................................................................. 3-5

Figure 3-8 Rotating Primary Ring - Outside Pressure (or Inside Mounted) .............................. 3-9

Figure 3-9 Rotating Primary Ring - Inside Pressure (or Outside Mounted) .............................. 3-9

Figure 3-10 Stationary Primary Ring - Outside Pressure (or Inside Mounted) ......................... 3-9

Figure 3-11 Stationary Primary Ring - Inside Pressure (or Outside Mounted) ....................... 3-10

Figure 3-12 Back-to-Back Dual Seal ..................................................................................... 3-10

Figure 3-13 Face-to-Face Dual Seal ..................................................................................... 3-11

Figure 3-14 Pressure Stage Tandem Seal ............................................................................ 3-11

Figure 3-15 Single Seal Cartridge ......................................................................................... 3-12

Figure 3-16 Balanced Stator Design Multi-Seal Cartridge Supplied by a Manufacturer fora Main Coolant Pump.................................................................................................... 3-13

Figure 3-17 Seal Stage Details of a Balanced Stator Design Multi-Seal CartridgeSupplied by a Manufacturer for a Main Coolant Pump................................................... 3-14

Figure 3-18 Common Variations in Seal Chamber Design .................................................... 3-15

Figure 3-19 A Typical Flush Plan for a Cooling Seal Chamber.............................................. 3-16

Figure 3-20 Unbalanced, Balanced, and Partially Balanced Seal Designs ............................ 3-19

Figure 3-21 Face Pressure Distribution Due to Hydraulic Pressure and Spring Force........... 3-21

Figure 3-22 Rotating Seal Balance Designs.......................................................................... 3-22

Figure 3-23 Pressure/Temperature Operating Envelope Showing 'T Margin Required forSeal Operation .............................................................................................................. 3-25

Figure 3-24 Seal Face with Thermal Hydrodynamic Grooves for Positive HydrodynamicLubrication..................................................................................................................... 3-26

Figure 3-25 Design Options with Hydrodynamic Grooves on the Outer Periphery or InnerPeriphery of Seal Face .................................................................................................. 3-27

Figure 3-26 Other Variations in Seal Face Geometry to Enhance Lubrication of theFaces ............................................................................................................................ 3-27

Figure 3-27 Hydrostatic Face Seal Design ............................................................................ 3-29


xiv

Figure 4-1 Lubrication Regimes at Seal Interface Showing Asperity Contact asLubrication Changes from Full Film to Mixed to Boundary............................................... 4-5

Figure 4-2 Extremes of Seal Face Distortion (Coning) Due to Thermal and PressureEffects ............................................................................................................................. 4-7

Figure 4-3 Pressure Distribution Changes Caused by Coning of the Seal Faces(for Outside Pressurized Seal)......................................................................................... 4-8

Figure 4-4 Changes in Seal Contact Area Under Constant Operating Conditions Duringthe Wear-In Process for a Seal With a Hard Face and a Soft Face ................................. 4-9

Figure 4-5 Example of a Wear-In Sequence (Stages 1 through 4) for a Mechanical Sealwith a Soft Seal Face....................................................................................................... 4-9

Figure 4-6 Fluid Pumping Action Across the Seal Faces Due to Static Offset andMisalignment ................................................................................................................. 4-11

Figure 4-7 Rotating Balance Seal Wobble Caused by Shaft Tilt ............................................ 4-12

Figure 4-8 Shaft Tilt Accommodated by Stationary Ring Pivot .............................................. 4-14

Figure 4-9 Seal Pumping Caused by Dynamic Offset of Rotating Narrow Face .................... 4-15

Figure 6-1 Seal Data Plot Showing Declining Performance..................................................... 6-4

Figure 8-1 Shaft Straightness Check....................................................................................... 8-5

Figure 8-2 Shaft Runout Measurement ................................................................................... 8-5

Figure 8-3 Stuffing Box Squareness Measurement ................................................................. 8-6

Figure 8-4 Shaft and Impeller Rotational Balance Check ........................................................ 8-6

Figure 8-5 Radial and Axial Bearing Clearance Checks .......................................................... 8-7

Figure 8-6 Measurement of Critical Shaft and Sleeve Diameters ............................................ 8-7

Figure 8-7 Sleeve Hardfacing to Prolong Life .......................................................................... 8-8

Figure 8-8 Lead-In Chamfers to Prevent Secondary Seal Damage During Installation............ 8-8

Figure 8-9 Seal Cavity Dimensional Checks Prior to Installation ............................................. 8-9

Figure B-1 Using an Optical Flat to Determine Seal Face Flatness Light Bands .....................B-2

Figure B-2 The Viewing Angle Typically Should be 80q to 90q While Checking FlatnessUsing a Monochromatic Light Source ..............................................................................B-3

Figure B-3 Flat Within One Light Band....................................................................................B-4

Figure B-4 Bands Bend on One side and Line AB Intersects 3 Bands ....................................B-5

Figure B-5 This Indicates an Egg-Shaped Curvature of 2.5 Light Bands .................................B-5

Figure B-6 Bands Show a Saddle Shape Out-of-Flat Condition of 3 Light Bands ....................B-6

Figure B-7 Bands Show a Cylindrical-Shaped Part with a 3-Light Band Reading Error ...........B-6

Figure B-8 Band Symmetrical Pattern Indicates a Conical Convex or Concave Part ...............B-6


xv

LIST OF TABLES

Table 2-1 Glossary of Terms................................................................................................... 2-1

Table 3-1 Secondary Seal Properties...................................................................................... 3-3

Table 3-2 Advantages and Disadvantages of Mechanical Face Seal Configurations............... 3-6

Table 3-3 Advantages and Disadvantages of Mechanical Face Seal Springs ......................... 3-8

Table 3-4 Approximate PV Limits psi-ft/min (Mpa-m/sec) for General Seals with VariousCombinations of Seal Face Materials and Fluids ........................................................... 3-23

Table 5-1 Seal Application and Selection Guidelines .............................................................. 5-2

Table 6-1 Seal System Log Sheet........................................................................................... 6-3

Table 7-1 External Symptoms of Seal Failure ......................................................................... 7-3

Table 7-2 Checklist of Actions Before Dismantling .................................................................. 7-7

Table 7-3 General Checks During Dismantling........................................................................ 7-9

Table 7-4 Premature Failure Checks During Dismantling ...................................................... 7-10

Table 7-5 Mid-Life Failure Checks During Dismantling.......................................................... 7-11

Table 7-6 Visual Examination: Failure Symptoms Based on Mechanical, Thermal, orChemical Damage......................................................................................................... 7-13

Table 7-7 Visual Examination: Symptoms, Characteristics, Causes and Remedies .............. 7-14


1-1

1 INTRODUCTION

1.1 Background

In the past, the Nuclear Maintenance Application Center (NMAC) of EPRI has published anumber of application and maintenance guides to provide technical guidance to engineers andother plant personnel on mechanical seal equipment and component operation. These haveincluded information on proper selection, installation, and failure mode analysis, andmaintenance recommendations designed to optimize equipment operating life. EPRI hasconducted and published the following documents relating to equipment seals:

x Guide to Optimized Replacement of Equipment Seals. March 1990 (NP-6731).

x Shelf Life of Elastomeric Components. 1994 (NP-6608).

x Main Coolant Pump Seal Maintenance Guide. 1993 (TR-100855).

x Static Seal Maintenance Guide. 1994 (TR-104749).

x Centrifugal and Positive Displacement Maintenance Guide. 1997 (TR-107252).

Mechanical seals are widely used in many types of rotating power plant equipment, especiallypumps of various sizes and pressure ratings. Even though mechanical seals are capable ofproviding reliable long-term service with proper consideration to design, application, installation,and maintenance, they still exhibit unsatisfactory performance, short life, and unpredictable(random) failures in some applications. As such, mechanical seals have a significant influence onthe reliability of plant equipment.

A mechanical seal is a complex assembly of precision-machined components. Design andprediction of mechanical seal performance in a given application requires an in-depth knowledgeof all mechanical disciplines: stress/deflection analysis, vibration analysis, heat transfer, fluidmechanics, lubrication, friction and wear, materials, and manufacturing processes.

Mechanical seal technology, as well as a fundamental understanding of how such seals work, hasevolved and improved significantly over the last two decades. This has been the result ofextensive industry-wide research, testing, plant experience, availability of sophisticatedanalytical tools (for example, computational fluid dynamics analysis and finite element analysis),and advances in manufacturing technology. This has enabled improvements in the performanceof mechanical seals in a number of critical applications in nuclear and fossil power plants,petrochemical plants, and other industries.


Introduction

1-2

1.2 Purpose

The objective of this NMAC Mechanical Seal Maintenance and Application Guide is to providepersonnel in nuclear and fossil power plants with:

x An in-depth understanding of the design and operation of mechanical seals

x Correct selection of mechanical seals for an application

x Proper installation methods

x Guidance on failure mechanisms and their causes, including troubleshooting information

x Guidance on expected seal life under various operating conditions

x Recommended predictive (diagnostics), preventive, and corrective methods of maintenanceto optimize seal life

x Training material to support personnel training

This guide presents the latest developments in mechanical seal technology and materials. Someof the new seal designs are already in use in industries other than power plants. Their viability inpower plant operation was researched and, based on this research, the guide includesrecommendations for achieving plant-wide improvements in nuclear and fossil power plants.

This NMAC Mechanical Seal Maintenance and Application Guide is a comprehensive, state-of-the-art text for nuclear and fossil power utility engineers.

1.3 Approach

A detailed review of the available literature was conducted to establish the state of technology inmechanical seals [1-65*]. The objective was to establish the present state of the art regarding:

x The operation of seals

x Designs offered by the manufacturers

x Application problems

x Solutions to address these problems

x Installation and maintenance recommendations

x Statistical/failure data

x Plant experiences

x Emerging technologies

All relevant technical papers, reports, and publications were reviewed from:

x The American Society of Mechanical Engineers (ASME)

* Numerals in brackets denote references listed in Section 9 of this Guide.


Introduction

1-3

x The American Society of Lubrication Engineers (ASLE)

x The British Hydromechanics Research Association (BHRA)

x The Institution of Mechanical Engineers (IME)

x Seal manufacturers

The review included both domestic and international mechanical seal manufacturers such as JohnCrane Company, Chesterton, Borg-Warner, Durametallic, Sealol, AST, Burgmann Seals,Flexibox, Latty International. Significant United States Nuclear Regulatory Commission GenericCommunications relating to shaft seal issues were also reviewed and evaluated to developsuitable recommendations for inclusion in this guide.

Additionally, a questionnaire was developed as a survey distributed among the nuclear and fossilpower utilities to facilitate determination of specific problems and commonly encountered failuremodes. The results of the survey were analyzed to determine the root causes of seal failure, todevelop troubleshooting, failure diagnosis, installation and maintenance guidelines, and todevelop suitable recommendations for this guide. This guide also utilizes relevant data fromtechnical papers, as well as principal investigators’ experience with mechanical seals in thepetrochemical, chemical, drilling, and mining industries.

1.4 Highlighting of Key Points

Throughout this guide, key information is summarized in Pop Outs. Pop outs are bold-letteredboxes that succinctly restate information covered in detail in the surrounding text, making thekey point easier to locate.

The primary intent of a pop out is to emphasize information that will allow individuals to takeaction for the benefit of the plant. The information included in these pop outs was selected byNMAC personnel and the consultants and utility personnel who prepared and reviewed thisguide.

The pop outs are organized according to three categories: O&M Costs, Technical, and HumanPerformance. Each category has an identifying icon, as shown below, to draw attention to itwhen quickly reviewing the guide.

Key O&M Cost Point

Emphasizes information that will result in reduced purchase, operating, ormaintenance costs.

Key Technical Point

Targets information that will lead to improved equipment reliability.


Introduction

1-4

Key Human Performance Point

Denotes information that requires personnel action or consideration in orderto prevent injury or damage, or ease completion of the task.

Appendix D contains a listing of all key points in each category. The listing restates each keypoint and provides reference to its location in the body of the report. By reviewing this listing,users of this guide can determine if they have taken advantage of key information that theauthors believe would benefit their plants.


2-1

2 GLOSSARY OF TERMS

The terminology used to describe the various design features, configurations, applications,installation, and performance of mechanical face seals has evolved over the years. Sealhandbooks, manufacturer catalogs, technical papers, and the industry standards for both theUnited States of America and European countries [3-9] were reviewed to reconcile thedifferences in definitions and prepare the following comprehensive glossary (Table 2-1) of termsin common use today and adopted in this guide.

Table 2-1Glossary of Terms

Term Definition

Abeyance seal A non-contacting auxiliary seal that is activated by failure of the primary seal in thecase of a single seal, or the outer seal in the case of a double seal.

Abrasive wear Wear occurring by the mechanical action of an abrasive. Abrasives are substancesthat are harder than the abraded surface and usually have an angular profile.

Adhesive wear Wear arising from small-scale local welding at asperities; a common wear modeassociated with running in and mild steady state wear.

Anti-rotation pinor device

A device, usually a pin, designed to prevent the stationary seal member fromrotating in its mounting.

API 610 API Standard: Centrifugal Pumps for General Refinery Services (8th Ed. inpreparation). A specification widely used for heavy duty centrifugal pumps.

API 682 API Standard: Shaft Sealing System for Centrifugal and Rotary Pumps (1st Ed.,1994).

API piping plan Arrangements recommended in API 610 for connecting auxiliary pipework to theseal chamber.

Asperity Minute high spot on the seal face resulting from the manufacturing process.

Autobalancing Alternative term for double balancing (see double balancing).

Auxiliary seal A seal fitted to the atmospheric side of a quench chamber or secondary-containment chamber.

Back-to-back seal A seal configuration consisting of a double seal with the seal rings adjacent to eachother, that is, two mechanical seals facing in opposite directions.

Back-up seal Alternative name for auxiliary seal.

Balance diameter See note under balance ratio.


Glossary of Terms

2-2

Table 2-1 (cont.)Glossary of Terms

Term Definition

Balance ratio Balance ratio determines the proportion of the seal chamber pressure that is appliedto the faces of a mechanical seal. Mechanical seals are available as both balancedand unbalanced designs. The balance ratio is a ratio of the area subjected to thedifferential pressure of the fluid to the area between the seal ring faces. Seals areoften identified by their balance diameter. The balance diameter, Db, is locatedbetween the inside diameter, Di, and outside diameter, Do, of the seal ring contactarea.

For seals pressurized on the outside diameter:

2i

2o

2b

2o

DD

DD Ratio Balance

�

�

For seals pressurized on the inside diameter:

2i

2o

2i

2b

D - D

D - D Ratio Balance

Note: Balance diameter varies with seal design, but for spring pusher seals underouter diameter (OD) pressure, it is normally the diameter of the sliding contactsurface of the inner diameter (ID) of the dynamic O-ring. For spring pusher sealsunder inner diameter pressure, it is normally the diameter of the sliding contactsurface of the outer diameter of the dynamic O-ring.

For welded metal bellows type seals, the balance diameter is normally the meandiameter of the bellows but this can vary with pressure. As stated in Diametral Tiltand Leakage of End Face Seals with Convergent Sealing Gaps [26], the balancediameter for the welded bellows is equal to the root mean square average of thebellows OD and ID, that is, Db = [0.5 (OD2 + ID2)]1/2.

Balanced seal A mechanical seal arrangement whereby the effect of the hydraulic pressure in theseal chamber on the seal face closing forces has been reduced through sealgeometry. Balanced seals have a seal balance ratio of less than 1 (0.65 to 0.85 istypical range).

Balanced sleeve/secondary sealsleeve

Stationary balance seal designs allow the stationary member to move axially. Thesecondary seal slides on a sleeve, or insert, called the balance sleeve.

Barrier fluid A fluid injected between dual mechanical seals to completely isolate the pumpprocess liquid from the environment. Pressure of the barrier fluid is always higherthan the process pressure being sealed. (For contrast, see buffer fluid definition.)

Bellows seal A type of mechanical seal in which one of the faces is mounted on an elastomericor a flexible metal bellows to provide secondary sealing. Metal bellows, and insome designs elastomeric bellows, also provide spring-type loading to the sealfaces.

Blistering A term used to describe a particular form of damage to carbon-graphite seal faces,usually caused by hydrocarbons.

Boundarylubrication

Condition of lubrication where the seal faces are in solid contact, though separatedby adsorbed surface films.


Glossary of Terms

2-3


Term Definition

Bubble point Mixtures of liquids do not have a clearly defined boiling point. The bubble point isthe temperature at which the first bubble is evolved on raising the temperature atconstant pressure. The term is most frequently used with mixtures of hydrocarbons.

Buffer fluid A fluid used as a lubricant or buffer between dual mechanical seals. The fluid isalways at a pressure lower than the pump process pressure being sealed. (Forcontrast, see barrier fluid definition.)

Cartridge seal A completely self-contained mechanical face seal unit (including seal, gland,sleeve, and mating ring) that is pre-assembled and requires no field adjustments.

Clamp plate An alternative term for seal plate.

Closing force Combined hydraulic and spring load acting on the floating seal member in theclosing direction.

Coking The formation of carbonaceous deposits on the atmospheric side of a mechanicalseal resulting from the oxidation/polymerization of leakage of organic products.

Compression set The difference between the thickness of a gasket, or elastomer, or length of aspring, both as supplied and after being subject to compression in service. Morespecifically, the compression set of an elastomer is defined as:

lengthspecimen originalstrain x applied

lengthspecimen in change

Coning Axisymmetric distortion of the seal faces, causing a rotation of the seal ring cross-section and creating a radial variation in seal film thickness.

Contact pattern An alternative term for wear track.

Controlled bleed-off (CBO) orstaging flow

Staged seal designs use an orifice to bypass a small flow around each seal to reducepressure to subsequent stages. If the resistance of each orifice device is equal, andthe seals are not leaking, the differential pressure across each stage will be equal.This distribution of pressure provides the optimum condition to obtain themaximum seal life.

Controlledleakage seal

Alternative term for hydrostatic seal.

Convergence/divergence

It is necessary to have an adequate gap at the inner or the outer periphery of theseal faces that is exposed to the pressurized fluid to allow fluid to enter and providelubrication and cooling. Coning of seal faces can cause the gap to decrease(converging seal faces) or increase (diverging seal faces) in the direction ofleakage.

Coolant A liquid from an external source circulated through a stationary seal member orother separate cooling element to remove heat.

Criticaldimensions

Each specific seal design has a unique geometry. In this geometry some dimensionsare very important to the successful operation of the seal. Other dimensions,although important, might not have a significant effect as they vary withinreasonable values. Dimensions that are very important to the proper operation ofthe seal are termed critical dimensions. These might be very precise dimensions,such as seal face flatness, or they might have tolerances of 1/16" (.16 cm), such as aspring gap. Generally, critical dimensions are verified and recorded to ensure theyare correct.


Glossary of Terms

2-4


Term Definition

Crystallization The formation of crystalline solids on the atmospheric side of a mechanical sealresulting from evaporation of product leakage (for example, borated water).

Cyclone separator Hydrocyclone fitted in a product recirculation line to remove solids.

Dead-ended Seal arrangement in which there is no product recirculation or injection of flushinto the seal chamber.

Degree of balance The proportion of the face area that is exposed to the low-pressure side of thebalance diameter ( = 1 – balance ratio).

Delta T, 'T The difference between the bulk temperature of the liquid in the seal chamber andthe boiling point (or bubble point in the case of mixtures) of this liquid at thepressure in the seal chamber. Also known as the product temperature margin.

Destaging When individual seal stages leak more than other stages, the differential pressureacross the stages that are not leaking increases, and the differential pressure acrossstages that are leaking decreases. This shift in differential pressures is termeddestaging.

Diameter ratio The ratio (>1) between the outer and inner diameters of the narrower of the sealfaces.

Double balancing A mechanical seal design feature that changes the balance diameter to improve theseal's resistance to operating under reverse pressure. This prevents opening of theinside seal in a double seal upon loss of barrier fluid pressure. (Sometimes calledautobalancing.)

Double seal Restricted in this publication to the arrangement of two mechanical seals in a sealchamber sealing in opposite directions. The seals can be either the back-to-back orface-to-face seal configuration (qv).

Note: An alternative usage is to include two seals sealing in the same directionin the category of double seal; in this publication, the latter configuration isreferred to as a tandem seal.

Drain connection A connection to the quench (or secondary containment) chamber for the collectionof liquid.

Drive collar The part of a cartridge seal that mechanically connects the sleeve to the shaft totransmit rotation and prevent axial movement of the sleeve relative to the shaft.

Drive pin A device for transmitting torque from the shaft to the rotating seal member.

Dry running Running with no liquid between the seal faces.

Dual mechanicalseal

A seal arrangement using more than one seal in the same seal chamber in anyorientation that can utilize either a pressurized barrier fluid or a non-pressurizedbuffer fluid. (It is also referred to as a double or tandem seal.)

Dynamicsecondary seal

A secondary seal in a pusher seal that prevents leakage between the shaft orhousing and the floating seal member of a mechanical seal.

Early-life failures Failures occurring shortly after start-up because of manufacturing or fitting errors;sometimes referred to as infantile mortality.

Elastomer Non-metallic parts such as O-rings, U-cups, quad-rings, and bellows.


Glossary of Terms

2-5


Term Definition

Erosion Abrasive wear of a surface by small particles in a gas, vapor or liquid, or dropletsof liquid in a gas or vapor (wire-drawing) flowing across it.

Externallymounted seal(also calledoutside mounted).

An arrangement in which the mechanical seal is mounted outside the pump orsealed vessel so that fewer seal parts are exposed to contact with a corrosive sealedfluid. In this arrangement, the sealed fluid is in contact with the inner diameter ofthe seal faces.

Face This term is used in a strict sense to mean the surface of a seal ring at the sealinginterface, but is also commonly used for the whole ring, for example, hard face.

Face load The combined spring and hydraulic load carried between the seal faces beforeallowing for any fluid pressure in the sealing interface.

Face plate The primary sealing surface in a hydrostatic seal is a ceramic piece called thefaceplate. Some faceplates are stainless steel coated with aluminum oxide andothers are silica nitride.

Face width Half the difference between the outer and inner diameters of the narrower of theseal faces.

Face-to-face seal A seal configuration consisting of a double seal with the seats adjacent to eachother, that is, two mechanical seals facing in opposite directions.

Film thickness The thickness of the fluid film between the seal faces.

Film transfer A process by which a film of the material of the soft face is deposited on the hardface.

Fitness testing Cartridge seals are assembled outside the pump and can be tested to verify theassembly. Normally, a test vessel (with adequate ports, nozzles, gauges, and a flowmeter) is used to measure staging pressures and controlled bleed-off flow.Frequently, fitness testers are supplied as skid-mounted assemblies with therequired pumps, reservoirs, instrumentation, and connecting piping.

Flashing A rapid change in fluid state, from liquid to gaseous. In a dynamic seal, this canoccur when frictional energy is added to the fluid as the latter passes between theprimary sealing faces, or when fluid pressure is reduced below the fluid's vaporpressure because of a pressure drop across the sealing faces. In this publication, thedefinition of flashing is that vapor pressure is greater than 1 bar (14.5 psia) atpumping temperature.

Flashinghydrocarbonservice

Any service that requires vapor suppression by cooling or pressurization to preventflashing. This category includes all hydrocarbon services where the fluid has avapor pressure greater than 1 bar (14.5 psia) at pumping temperature.

Flatness The degree of flatness (peak-to-valley amplitude) of the seal faces, normallyexpressed in helium light bands (1 helium light band = 11.6 micro-inches (0.29Pm)).

Flexible graphite A pure carbon graphite material used for static gaskets in mechanical seal design,both for cryogenic and hot service.

Floating sealmember(also calledprimary ring)

The spring-loaded seal member of a mechanical seal that is allowed limited axialmovement to accommodate shaft end float and seal wear.


Glossary of Terms

2-6


Term Definition

Fluid film A film of liquid separating the seal faces, generated by hydrostatic and/orhydrodynamic lubrication.

Fluid filmlubrication

Condition of lubrication in which the seal faces are completely separated by aliquid film.

Fluoroelastomer A type of O-ring material commonly used in mechanical seals, such as Viton.

Flush A small amount of fluid that is introduced into the seal chamber on the processfluid side in close proximity to the sealing faces and usually used for cooling andlubricating the seal faces and to prevent accumulation of solid particulates.

Flush connection Connection to the seal chamber to allow circulation of the sealed fluid.

Free length The unconstrained axial length of a mechanical seal.

Fretting A combination of corrosion and wear resulting from very small amplitude relativemotion. In a mechanical seal, a common example of fretting occurs when therubbing motion of a secondary seal continually wipes the oxide coating from ashaft or sleeve. The increased surface roughness of fretted surfaces can adverselyaffect the ability of the floating seal member to track its mating seal ring.

Frictioncoefficient

Defined in a mechanical seal as the ratio of the friction force at the sealing interfaceto the closing force.

Gland plate (Alternative term for seal plate.) An end plate that connects the stationary assemblyof a mechanical seal to the seal chamber.

Hang-up Failure of the secondary dynamic seal to move under the applied spring andhydraulic forces.

Hard face Seal face manufactured from ceramic, silicon carbide, or metal.

Header tank An external vessel providing a pressurized barrier fluid to a double seal, either witha static head or with a thermal siphon system.

Heat checking The formation of fine radial cracks on a hard seal face caused by thermal stressesset up by inadequately lubricated or dry running and quenching by the sealed fluid.

Heat exchanger A device for cooling a fluid by heat transfer. Heat exchangers might be internal tothe pump, or externally mounted and connected with piping spools. Typically,these heat exchangers also cool the water that passes through the pump waterbearing. Three types of construction are used for these heat exchangers: a tube-in-tube, a tube bundle, or a rotating baffle type. Cooling water might be provided fromthe component cooling water system (CCW).

Hook sleeve A cylindrical sleeve with a step or hook at the product end placed over the shaft toprotect it from wear and corrosion. This step is usually abutted against the impellerto hold it in place with a gasket between the shaft and the step (hook).

Hydraulic balance Same as balance ratio.

Hydraulic load The load on the floating seal member resulting from differential pressure betweenthe seal chamber and the low-pressure side of the seal acting on the area of thesealing ring above the balance diameter plus that caused by pressure on the low-pressure side acting on the area of the seal ring below the balance diameter.


Glossary of Terms

2-7


Term Definition

Hydrodynamiclubrication

Fluid-film lubrication in which the pressure in the fluid film is generated by therelative velocity between the seal faces; this can be in either a circumferential oran axial direction.

Hydrodynamicseal

A mechanical seal designed to operate with hydrodynamic lubrication between theseal faces.

Hydrostaticinstability

Face separation occurring when hydraulic opening forces exceed the total closingforce.

Hydrostaticlubrication

Fluid-film lubrication in which the pressure in the fluid film is generated externallyto the seal faces, and is used to maintain separation of the seal faces.

Hydrostaticopening force

The separating force on the seal faces resulting from the hydrostatic pressurebetween the faces.

Hydrostatic seal A mechanical seal designed to operate with hydrostatic lubrication between the sealfaces. Some seals in use as main coolant pump seals are of hydrostatic film ridingtaper face design. These seals use large converging gap geometry designed toseparate the seal faceplates by introducing pressurized fluid before the pump isrotated.

Icing Build-up of ice on the outside of a mechanical seal caused by solidification ofatmospheric water vapor through evaporative cooling of leakage of a liquid sealedabove its atmospheric boiling point.

Inside mountedseal (or internallymounted)

The common arrangement with the mechanical seal mounted inside the pump orsealed vessel. No parts of the seal's flexible element or stationary faces are outsidethe gland. In this arrangement the sealed liquid is in contact with the outer diameterof the seal faces.

Internalcirculating device

A device located in the seal chamber to circulate seal chamber fluid through aninternal cooler area or an external cooler barrier/buffer fluid reservoir. Usuallyreferred to as a pumping ring.

L10 life A statistic used to express the life of a population of mechanical seals; it is the timewhen 10 percent of the seals have failed.

Lapping Abrasive machining to achieve a very flat surface is called lapping. It can beperformed by hand on a plate or by a lapping machine. A lapping machine rotates aflat surface and the parts being lapped, with respect to each other, using an abrasiveas a cutting agent between the two. Abrasives used include diamond compound,aluminum oxide compound, and silicon carbide compound.

Leakage Sealed fluid loss from the system; it includes non-obvious vapor formed byevaporation, as well as the more obvious liquid emission. Leakage might occurthrough secondary as well as primary seals.

Leakage rate The volume of fluid (compressible or incompressible) passing through a seal in agiven length of time. For compressible fluids, leakage rate is normally expressed instandard cubic feet per minute (SCFM), and for incompressible fluids, in terms ofcubic centimeters per minute.

Light band Refers to the wavelength of helium light (= 11.6 micro-inches, or 0.29 Pm) used asa measure of the flatness of the seal faces.


Glossary of Terms

2-8


Term Definition

Mating ring A disc- or ring-shaped member, mounted either on a shaft sleeve or in a housing,that provides the primary fluid seal when in proximity to the face of an axiallyadjustable face seal assembly.

Maximumallowableworking pressure(MAWP)

The greatest discharge pressure at the specified pumping temperature for which thepump casing is designed.

Maximumdynamic sealingpressure (MDSP)

The highest pressure expected at the seal (or seals) during any specified operatingcondition and during start-up and shutdown. In determining this pressure,consideration should be given to the maximum suction pressure, the flush pressure,and the effect of clearance changes with the pump.

Maximum staticsealing pressure(MSSP)

The highest pressure, excluding pressure encountered during hydrostatic testing, towhich the seal (or seals) can be subjected while the pump is shut down.

Main coolantpump (MCP)

The term used to describe a group or family of reactor coolant pumps used inpressurized water reactors, and reactor recirculation pumps used in boiling waterreactors, is main coolant pumps (MCP).

Mechanical seal A device for sealing a rotating shaft whereby the sealing interface is locatedbetween a pair of radial faces, one rotating, the other stationary.

Mixed lubrication Condition of lubrication where the load between the seal faces is partly carried byboundary lubrication and partly by fluid-film lubrication.

Mean timebetween failures(MTBF)

Mean time between failures. A statistic used to express the life of a population ofmechanical seals. It is given mathematically by the expression

n

LLMTBF 21 nL . . . ��

where L1, L2, etc., are the lives of individual seals.

Neck bush Closed clearance bush at the inner end of seal chamber to restrict flow of dirty fluidfrom pump into the seal chamber or to maintain pressure of recirculation flow inseal chamber.

Net closing force The difference between the total closing force and the hydrostatic opening force.

Non-flashing A fluid state that does not change to a vapor phase at any operating condition oroperating temperature.

Non-flashinghydrocarbonservice

This category includes all hydrocarbon services that are predominately allhydrogen and carbon atoms; however, other non-hydrocarbon constituents mightbe entrained in the stream. A product in this category does not require vaporsuppression to prevent transformation from a liquid phase to a vapor phase. For thispublication, the definition of non-flashing means that the vapor pressure is less than1 bar (14.5 psia) at pumping temperature.

Non-hydrocarbonservice

This service category includes all services that cannot be defined as containing allhydrogen and carbon molecules. However, some hydrocarbons might be entrainedin the fluids. Included in this category are boiler feed water (and other waterservices), borated water, caustics, acids, amines, and other chemicals commonlyused in refinery services.


Glossary of Terms

2-9


Term Definition

Non-pusher typeseal

A mechanical seal (usually metal bellows) in which the secondary seal is fixed tothe shaft. A bellows seal is an example of a non-pusher seal in which the dynamicsecondary seal is eliminated.

Operating length Axial length of installed mechanical seal.

Optical flat An optical flat is a precision ground quartz or Pyrex plate. When light waves reflectoff the lapped surface through the flat, light bands are visible. The greater the gapbetween the flat and the lapped surface, the larger the number of light bands. Whenused with a monochromatic light (emits only one wavelength visible light), thenumber of light bands can be used to measure the flatness of the lapped parts.

Orifice nipple A pipe nipple made of solid bar stock with an orifice drilled through it to regulatethe flush flow commonly found on Plan 11 systems described in API 682. Thenipple should be welded to the discharge casing.

O-ring Toroidal sealing ring with an O-shaped (circular) cross-section, used as asecondary seal or gasket in both static and dynamic situations.

Outside mountedseal

See externally mounted seal.

Perfluoro-elastomer

High temperature, chemical resistant O-ring material such as DuPont DowElastomer, Kalrez® or Green Tweed, Chemraz®. This material requires a widerO-ring groove than standard O-ring materials.

Popping A term used to indicate intermittent leakage of vapor resulting from a rapid changein fluid state from liquid to gaseous and characterized by a popping sound.

Pressurebreakdown cells/staging coils

Staged seal designs in MCPs use an orifice to bypass a small flow around each sealto reduce pressure to subsequent stages. This configuration allows pressure to beevenly distributed at each seal stage. The orifice is usually either a series of small,machined grooves or a coil of small diameter tubing. These breakdown devices arereferred to as pressure breakdown cells or staging coils.

Pressure casing The composite of all stationary pressure-containing parts of the seal, including sealchamber, seal gland, and barrier/buffer fluid chamber (container) and otherattached parts, but excluding the stationary and rotating members of the mechanicalseal.

Primary seal Mechanical seals have a rotating seal ring and a stationary seal ring. Fluid sealingoccurs at the interface of the rotating ring and the stationary ring. The seal thatoccurs at this interface is often referred to as the primary seal.

Primary ring See floating seal member.

Product The process fluid.

Productrecirculation

Circulation of the product through the seal chamber to provide cooling (seerecirculation flow, reverse circulation).

Producttemperaturemargin

Alternative name for Delta T, 'T.

Pumping ring A device fitted inside the seal chamber to circulate the liquid in the seal chamberthrough an external cooler and/or header tank.


Glossary of Terms

2-10


Term Definition

Pusher type seal A mechanical seal in which the secondary seal (for example, an O-ring, U-cup,plastic wedge ring) is mechanically pushed (and therefore can move) along theshaft or sleeve to compensate for face wear. Bellows are not classified as pushertype seals.

PV factor A parameter used to express the severity of operating conditions for a mechanicalface seal. In this publication, it is defined as the product of the pressure drop acrossthe seal and the mean relative velocity of the seal faces.

Quench A neutral fluid, usually water or steam, introduced on the atmospheric side of theseal to retard formation of solids or crystallization of dissolved solids that mightinterfere with seal movement.

Quench chamber Enclosed space on the atmospheric side of a mechanical seal to which the quench isintroduced; normally fitted with an auxiliary seal to prevent excessive leakage tothe atmosphere.

RMS or Ra Root mean square or roughness average – terms used to define surface roughness.

Random failures Failures occurring during operation, other than early-life failures and those causedby normal wear-out of the seal faces.

Recirculation flow Flow of the product from the pump discharge through the seal chamber to the backof the pump impeller, or from the back of the pump impeller through the sealchamber to the pump suction.

Recirculationimpeller

Many MCPs have external heat exchangers mounted to the pump motor stand.These heat exchangers require the fluid to be pumped from the seal/bearing cavityto the heat exchanger and back. The recirculation impeller is normally a shaft-mounted, axial flow-type impeller. Flow rates are normally in the range of 30 to 50gpm (113 to 189 lpm) for MCPs.

Reverse balancing Selection of the balance diameter so that a mechanical seal can withstand pressureon the inside diameter of its face rather than on the outside diameter, that is, thereverse of normal outside diameter pressurization. This is of particular use for theinboard seal of a double seal as it puts any solids on the outside diameter of theinboard seal and minimizes clogging.

Reversecirculation

Flow of the product from the back of the pump impeller through the seal chamberto the pump suction to provide cooling of the seal and reduce access of solids to theseal faces.

Rotating balance A rotating balance seal has the balance diameter Db on the rotating member.

Rotating seal Mechanical seal in which the floating seal member is mounted on the shaft.

Rotating sealmember

The seal member that is mounted on the shaft, either directly or on a sleeve thatrotates with the shaft.

Rotation (coning) Rotation (or conical deformation) of the seal ring cross-section due to torsionalring-type axisymmetrically-distributed load applied by the differential pressure orthermal load.

Seal arrangement The way in which a seal is mounted in the seal chamber and the method ofexercising control over the liquid in the seal chamber, viz, dead-ended, productrecirculation (see also API piping plan).


Glossary of Terms

2-11


Term Definition

Seal balance ratio See balance ratio.

Seal cavity The seal assembly fits inside the pump between the shaft and housing. The areathat the seal fits into is referred to as the seal cavity.

Seal chamber The region between the shaft and the pump case (housing) into which the shaft sealis installed.

Seal configuration The design or style of the primary seal (for example, pusher seal, bellows seal,double seal).

Seal envelope The external dimensions of a mechanical seal.

Seal environment The physical and chemical conditions prevailing in the seal chamber.

Seal face width The radial dimension of the sealing face measured from the inside edge to theoutside edge.

Seal face(s) The surfaces of the seal ring and seat in contact with each other.

Seal head Assembly consisting of primary ring, spring, retainer, set screw, and secondary seal(see Figure 3-1).

Seal injection Plant designs include MCPs both with and without seal injection. Many sealdesigners prefer units with seal injection, believing these installations to be morereliable. Seal injection is taken off the charging and volume control system onPWRs and off the control rod drive system for BWRs. Seal injection provides asource of cool filtered water entering the pump seal cavity. Filter sizes typicallyrange from 2 Pm to 20 Pm and the supply temperature is usually between 110°F(43°C) and 120°F (49°C).

Seal plate A plate that is bolted to the seal chamber and carries the stationary seal member.

Seal referencedimension

A reference mark scribed on the shaft to ensure that a mechanical seal is fitted withthe correct operating length.

Seal ring The floating seal member (sprung seal member) that contacts the mating ring. Itcan be either the stationary or rotating seal member.

Seal setting The proper relative position of the rotating portion of the seal to the stationaryportion of the seal is necessary to establish the proper seal spring force. Theprocess of establishing this position is termed setting the seal. Some designs do notrequire any adjustments, only that certain dimensions be measured to confirm theseal setting dimensions. Other designs rely on taking measurements on theassembled seal prior to installation, then establishing the same reference dimensiononce the seal is installed in the pump.

Seal size The maximum diameter of the shaft that will pass through the seal, that is, thediameter of the shaft (or shaft sleeve) to which the mechanical seal is fitted.(Alternative definitions based on other dimensions, for example, balance diameter,are also in current use).

Seal springs Staged seals use coil springs to create closing force at low pressures. The forcefrom the springs must be great enough to overcome the frictional forces from thesecondary seal, but not to cause unacceptably high contact pressure when the sealis operating at low pressures.


Glossary of Terms

2-12


Term Definition

Seal tooling Some mechanical face seals require special tools for inspection, assembly,installation, removal, and refurbishment. This collection of special tools isgenerally referred to as seal tooling. Seal tooling should be carefully controlled toensure that the tools are not lost or discarded. Attempts to perform sealmaintenance with inadequate tooling can result in equipment failures.

Sealant Alternative term for barrier fluid.

Sealed fluid Fluid in the seal chamber.

Sealed pressure Fluid pressure in the seal chamber.

Sealing interface Contact area between the seal ring and the seat.

Seat The axially fixed (unsprung) sealing element. It can be either the stationary orrotating seal member.

Secondarycontainment

An arrangement with a chamber on the atmospheric side of a mechanical seal tocontain high leakage consequent on failure. This chamber is normally fitted with anauxiliary seal.

Secondary seal Seal used to prevent leakage through paths alternative to that between the sealfaces. See dynamic and static secondary seals.

Secondary sealland

That part of the shaft or seal sleeve in contact with the dynamic secondary seal.

Service condition The maximum/minimum temperature and pressure under static or dynamiccondition.

Shaft sleeve A sleeve fitted between the shaft and a mechanical seal to provide a wear-resistantand replaceable secondary seal land. The sleeve is sealed to the shaft withelastomers.

Shelf life Some mechanical face seal components have a specific shelf life. These parts areusually elastomers that have a shelf life of 5 to 10 years when properly stored.Additionally, lapped parts should always be verified prior to installation.Occasionally, lapped parts will distort over time and need to be relapped prior toinstallation.

Single seal A seal arrangement with only one mechanical seal regardless of whether other sealtypes (for example, throttle bush, lip seal) are included in the seal arrangement.

Slotted seal glandplate

A gland plate with slots instead of holes for the mounting studs.

Soft face Seal faces manufactured from a relatively softer material (for example, carbon-graphite or PTFE) as compared to a harder mating seal face material (for example,tungsten carbide).

Solid length The axial length of a fully compressed mechanical seal.

Specific load Face load per unit area of sealing interface.

Spring load The load on the floating sealing element exerted by the seal spring(s).

Spring pressure The average seal face pressure due to spring load.


Glossary of Terms

2-13


Term Definition

Stage Many MCP seals use multiple mechanical seals in series, each seal having apredetermined differential pressure created by the controlled bleed-off. Eachindividual seal in this style design is termed a stage. Seals of this type of design aretermed staged seals.

Start-up torque The torque transmitted/absorbed by a mechanical seal on start-up.

Static secondaryseal

Seal used to prevent leakage between assembled parts that are not subject torelative motion in service, for example, between seal sleeve and shaft, betweenstationary seal member and seal plate.

Stationary balance A stationary balance seal has the balance diameter Db on the stationary member.

Stationary seal Mechanical seal in which the floating seal member is mounted on the seal plate.

Stationary sealmember

The seal member that is mounted on the seal plate.

Stationary sealring

The stationary seal ring is mounted in a supporting piece called a gland, carrier,holder, or ring support. In staged seal designs, the seal ring is generally a softmaterial, normally carbon graphite. In hydrostatic seals, the stationary memberconsists of an aluminum oxide or silica nitride faceplate mounted on a ring support.

Stator Alternative term for stationary seal member of a mechanical seal.

Stuffing box Alternative name for seal chamber, carried over from soft-packing technology.

Tandem seal Seal configuration consisting of a pair of mechanical seals mounted in series (thatis, two mechanical seals sealing in the same direction).

Thermal stressfailure

Alternative term for heat checking.

Throat bushing A device that forms a restrictive close clearance around the sleeve (or shaft)between the seal and the impeller.

Throttle bush A close-fitting bush around the shaft to restrict flow; can be used at the inner end ofthe seal chamber (neck bush) or as an auxiliary seal.

Throttle bushing A device that forms a restrictive close clearance around the sleeve (or shaft) at theoutboard end of a mechanical seal gland.

Total closingforce

The sum of the hydraulic load and spring load acting on the floating sealingmember to close the seal faces.

Total indicatedrunout (TIR)

Also known as total indicator reading, is the runout of a diameter or facedetermined by measurement with a dial indicator. The indicator reading implies anout-of-squareness or an eccentricity equal to half the reading. TIR is measured bysecuring a dial indicator to either the stationary or rotating component, setting thedial indicator to zero, and then rotating either component.


Glossary of Terms

2-14


Term Definition

Toxicity rating Classification of fluid toxicity defined in N. Irving Sax Dangerous Properties ofIndustrial Materials, 1984.

Toxicity Rating:

0 = No harmful effects under normal conditions

1 = Short-term effects that disappear once exposure is removed

2 = May produce both short- and long-term effects, but normally not lethal

3 = May cause death or permanent injury even after short exposure to onlysmall quantities

U = Insufficient data available on humans

Unbalanced seal A mechanical seal in which the balance ratio is greater than or equal to 1.

U-ring A "U" section dynamic secondary seal.

Vent connection A connection to the seal chamber for eliminating gas or vapor from the sealchamber. This is normally accomplished through a gland connection, such as theflush connection.

Volatilehazardous airpollutants(VHAP)

Any compound as defined by Title I, Part A, Section 112 of the National EmissionStandards for Hazardous Air Pollutants (Clean Air Act Amendment).

Volatile organiccompound (VOC)

Term used by various environmental agencies to designate regulated compounds.Emissions are measured as PPM with a calibrated analyzer.

V-ring A V section dynamic secondary seal.

Waviness Deviation of the seal faces from circumferential flatness. Waviness can be presenton the faces as manufactured or can develop after running.

Wear track The wear mark of the narrower seal face on the wider one.

Wedge ring A wedge-section dynamic secondary seal, usually manufactured from PTFE.

Support surface Most seal designs provide some type of support surface for the seal rings to controlseal ring deflection. Different terminology might be used for these surfaces, such asseat or back seat. In this publication, surfaces controlled to limit seal ringdeflections will be referred to as support surfaces.

Thermal barrier Most MCP designs are insulated from the high Reactor Coolant System (RCS)temperatures by a thermal barrier. The thermal barrier reduces pump cover (ormain flange), pump water bearing, and shaft seal cavity temperatures.

Total outflow The combined flow, consisting of seal leakage and controlled bleed-off, whichleaves the seal cavity is referred to as total outflow. This flow rate is the amount offluid that leaves the seal cavity and is made up with injection or RCS that has beencooled through the seal heat exchanger.

Wear tracking The mating surfaces of both hydrostatic and hydrodynamic seals operate in closeproximity. The faces might either contact or have particulates contact the seal ringfaces, resulting in a circular grooving or wear pattern referred to as wear tracking.


3-1

3 TECHNICAL DESCRIPTION

3.1 Operating Principles and Basic Components of a Mechanical FaceSeal

A mechanical face seal is a dynamic seal that prevents leakage of pressurized fluid between arotating shaft and a stationary housing. Mechanical face seals are available in a variety ofconfigurations, and their selection depends on the application. However, no matter what theapplication is, all mechanical face seals operate on the same principle. Basically, the seal iscomprised of two rings, either of which rotates relative to the other. One of the rings is usuallymounted rigidly and the other is mounted so that it can flex and align axially and angularly withthe rigidly mounted ring. Dynamic sealing is achieved at the interface between the two rings, theprimary ring and the mating ring. The rings achieve a seal at the interface due to their very highface flatness. Typically, the two rings are made of dissimilar materials.

The essential elements of a mechanical face seal are illustrated in Figure 3-1. These elementsserve the functions of sealing dynamically and statically, loading the faces, and transmittingrotation to the ring. The essential elements are described below. Advantages and disadvantagesof various configurations of these elements are discussed in Table 3-2.

Figure 3-1Essential Components of a Mechanical Face Seal

Primary Ring: The primary ring is also called a seal ring. The primary ring is the floating sealelement that is usually spring-mounted and permits axial and angular alignment in the assembly.Depending on the application requirements, it can be either the rotating member as shown inFigure 3-1 or the stationary member as shown in Figure 3-10. The method in which the primary


Technical Description

3-2

ring is mounted is dictated by the application requirements because each configuration offersboth advantages and disadvantages. The mechanical face seal design or style is defined by theprimary ring configuration, that is, rotating primary ring, stationary primary ring, double seal,bellows seal, and so on.

Mating Ring: The mating ring is also called a seat or seal seat. The mating ring is the rigidlymounted element and can be installed in the housing as shown in Figure 3-1 or on the shaft asshown in Figure 3-10. Where the mating ring is installed is dependent upon the applicationrequirements and the preferred implementation of the primary ring.

Key Technical Point

Mechanical face seals come in a variety of configurations, materials, anddesigns for primary sealing faces, secondary seals, springs, drivemechanisms. Options also include unbalanced or balanced designs, whetherthe primary seal or the mating seal is rotating, and whether the fluidpressure is on the outside or the inside surface of the seal. Seal design for agiven application should be selected after a careful evaluation of trade-offs,as discussed in this section, Section 3.

Secondary Seal: Seals used to prevent leakage through paths alternative to that between the sealfaces. The secondary seals can be static or dynamic. Static secondary seals prevent leakagebetween assembled parts that are not subject to relative motion in service, for example, betweenseal sleeve and shaft, between stationary seal member and housing. Dynamic secondary sealsprevent leakage between the shaft or housing and the floating seal member.

The type of secondary seal depends on the fluid type, service pressure, and service temperature.Table 3-1 provides the operating temperature limits and properties of materials typically used forsecondary seals.



3-3

Table 3-1Secondary Seal Properties

TempMaterial

°F °C

AirPermeability

Properties

Nitrile -22 to 248 -30 to 120 0.25-1.00 • General purpose

• Low cost

• Oil resistant

• Attacked by ozone

EthylenePropylene

-58 to 302 -50 to 150 9.6 • Steam, ozone, acid, andalkali resistant

Silicone -67 to 392 -55 to 200 170-260 • Good at low temperature

• Easily damaged

• High permeability

Neoprene -31 to 248 -35 to 120 104 • Weather resistant

• Fair oil resistant

Fluoroelastomer 14 to 302 -10 to 150 0.32 • Oil, fuel, chemical resistant

PTFE -67 to 446 -55 to 230 • Resistant to virtually all fluids

Polyacrylate -22 to 347 30 to 175 1.5 • Hot oil and ozone resistant

Epichlorohydrin -40 to 302 -40 to 150 .015-0.70 • Oil resistant

• Low permeability

Metal Bellows -328 to 1202 -200 to650

• Positive seal

• Chemical resistant

HighTemperatureFluoroelastomer

12 to 545 -10 to 285 0.32 • Excellent chemical resistant

Spring

Springs are used to develop the contact load between the primary ring and the mating ring in theabsence of fluid pressure. The amount of face load generated can vary significantly depending onthe type of spring selected. The choice includes a single coil spring, multiple coil springs, metalbellows, non-metal bellows, wave or Belleville washer, and magnets (see Figures 3-2 to 3-7). Insome cases, such as bellows, the spring can serve both the face-loading function and thesecondary sealing function. Advantages and disadvantages of each type of spring aresummarized in Table 3-3.



3-4

Figure 3-2Multiple Coil Springs

Figure 3-3Single Coil Springs

Figure 3-4Corrugated Bellows

Figure 3-5Welded Bellows



3-5

Figure 3-6Rubber Bellows

Figure 3-7Belleville Washers

Drive Mechanism: All mechanical face seals require some kind of device to position theprimary ring axially and to transmit the rotation of the shaft to the primary ring to ensure thatrelative motion occurs only at the seal faces. The drive mechanism is designed such that it is notrigidly attached to the primary ring so that it does not prevent self-alignment between theprimary ring and the mating ring. The drive mechanism is typically a setscrew, locking collar,key, or wedge ring. In some designs, the secondary seal is used to transmit the torque to theprimary ring when sufficient friction can be developed at the secondary seal interface. The drivemechanism is also used to provide torque restraint to the stationary seal if the static secondaryseal does not develop sufficient friction to prevent the stationary seal from turning.

Seal/Flushing Chamber: An area around the seal is provided to permit heat transfer through thefluid and to allow flushing of contaminants such as abrasive particles or toxic media. In a single-seal configuration, flushing is accomplished by injecting a liquid into the seal chamber at ahigher pressure than the sealed product.



3-6

Table 3-2Advantages and Disadvantages of Mechanical Face Seal Configurations

Type of Seal Advantages Disadvantages

Internally-mountedprimary seal

• Better cooling - seal surrounded byproduct

• Pressure acts to close the seal faces(pressure assisted)

• Can therefore be used at highpressure

• Components in compression(preferable to tension)

• Rotating elements centrifugeparticles away from seal face

• Lower leakage due to centrifugalaction

• Most of the seal is inside machinehousing, less space required outsidehousing

• Seal leakage containment is simpler

• No access for visual inspection• Any repair/replacement is labor

intensive

Externally-mountedprimary seal

• Easier to install/replace

• Easier to inspect• Minimizes components in contact

with pumped fluid (corrosives, etc.)

• Subject to environmentalcontamination and externaldamage from other environmentalfactors

Rotating primaryseal

• Centrifugal action keeps particlesaway from flexible member

• Generally requires less axialenvelope, particularly outside sealchambers

• Smaller radial section for a givenshaft size

• Generally lower cost

Stationaryprimary seal

• Capable of higher speeds• Better able to cope with

misalignment (particularly angular)• Less prone to clogging if leaked

product is inside seal chamber• Will accept media with higher

viscosity• Less friction loss due to turbulence of

liquids

Balanced seal • Capable of much higher pressuresand/or speeds (enhanced Pressure,Velocity (PV) capability)

Unbalancedseal

• Smaller envelope, particularly radial

• No step required on shaft or sleeve• Lower cost



3-7

Table 3-2 (cont.)Advantages and Disadvantages of Mechanical Face Seal Configurations

Type of Seal Advantages Disadvantages

Non-metalbellows

• PTFE bellows used in very severecorrosive duties

• Rubber bellows seal low in cost• Eliminates sliding packing (hang-up

hysteresis, sleeve wear)

• Rubber bellows require speciallydesigned components in a varietyof materials to cope with differentmedia

Dynamic pusherseal

• More robust• Higher pressure/temperature/speed

capability• Rubber bellows require specially

designed components in a variety ofmaterials to cope with different media

• Less prone to fatigue failure• More tolerant to shock and vibration

Metal bellows • Eliminates sliding packing (hang-uphysteresis, sleeve wear)

• Can be used at higher temperatures

• Can be used at higher speeds• Inherently balanced without stepping

shaft/sleeve• More compact (particularly larger

sizes)

• Not suitable for high pressures

Single springseal

• Can be used for a flexible drive• Larger section, more robust• Better protection against corrosion

• Less prone to clogging• Smaller radial space• Low stiffness gives greater axial

tolerance on fitting

Multi-spring seal • Shorter axial length• Rotating seal can tolerate higher

speeds

• Independent of direction of rotation(some single spring designs are alsoindependent)

• More consistent loading onto face

Wave/Belleville • Small axial tolerance

Magneticcoupling

• Reduces axial length • Limited seal face loading• Requires the use of materials that

can be magnetized• Reduces the choice of materials

suitable for corrosive environments



3-8

Table 3-3Advantages and Disadvantages of Mechanical Face Seal Springs

Type of Spring Advantages Disadvantages

Single coil • Corrosion, blockage resistance

• Low stress levels

• Low cost

• Greater axial tolerance

• Uneven loading

• Requires more axial space

• Difficult to compress as sizeincreases

• May unwind/tighten at high speeds

Multiple coils • Less axial space required

• Even face loading

• Resists high speeds

• Less corrosion/blockage resistance

• High stress levels

• More costly

Wave/Bellevillewasher

• Saves space • High spring rate

• Generally high cost

Elastomer bellows • Also provides secondary seal

• Relatively inexpensive

• Cannot be used in all fluids

• Has temperature limitations

Corrugated/weldedmetal bellows

• Provides secondary seal

• Corrosion resistant

• High temperature

• High controlled spring rate

• Expensive

• Requires more space than coilsprings

• Provides little damping to vibration

3.2 Major Design Variations

Design variations of the basic mechanical face seal illustrated in Figure 3-1 permit extending theapplication range and life of the seal. The configuration variation description is based on twoprimary factors:

x Whether the primary ring is rotating or stationary

x Location of the pressure relative to the annulus

A combination of these two parameters results in the four configurations illustrated in Figures 3-8 through 3-11. Figures 3-8 and 3-9 show rotating primary rings where pressure is applied to theoutside diameter of the seal and the inside diameter of the seal, respectively. Conversely, Figures3-10 and 3-11 show a stationary primary ring with pressure on the outside and inside of the seal,respectively. A description of each configuration, with its advantages and disadvantages, is givenin Table 3-2.

Rotating Primary Ring - Outside Pressure: This configuration (Figure 3-8) is also referred toas a rotating primary ring - inside mounted. In this configuration, the primary ring is mounted onthe shaft inside the stuffing box and pressure is applied on the outside diameter of the seal faces.A major advantage of this setup is that the product surrounds the face seals to provide goodcooling.



3-9

Figure 3-8Rotating Primary Ring - Outside Pressure (or Inside Mounted)

Rotating Primary Ring – Inside Pressure: This configuration (Figure 3-9) is also referred toas rotating primary ring - outside mounted. In this configuration, the primary ring is mountedoutside the stuffing box and pressure is applied to the inside diameter of the seal faces. Thesedesigns are easier to install and inspect than the other configurations. Because the pressure worksto push apart the seal faces, this design is not suitable for high pressures.

Figure 3-9Rotating Primary Ring - Inside Pressure (or Outside Mounted)

Stationary Primary Ring – Outside Pressure: This configuration (Figure 3-10) is alsoreferred to as stationary primary ring - inside mounted. In this configuration, the primary ring ismounted on the housing inside the stuffing box and pressure is applied on the outside diameter ofthe seal faces. This design offers higher speed capability with ease of inspection. Because therotating ring does not have multiple parts, this configuration is less susceptible to imbalance.

Figure 3-10Stationary Primary Ring - Outside Pressure (or Inside Mounted)



3-10

Stationary Primary Ring – Inside Pressure: This configuration (Figure 3-11) is also referredto as stationary primary ring - outside mounted. In this configuration, the primary ring ismounted on the housing inside the stuffing box and pressure is applied on the outside diameter.This design also offers high-speed capability and is less susceptible to imbalance due to a singlerotating ring.

Figure 3-11Stationary Primary Ring - Inside Pressure (or Outside Mounted)

3.3 Multiple Seals

Some applications require the use of multiple seals to provide for flushing or barrier fluids, orpressure staging to deal with higher pressures. Flushing is used to remove contaminants, to coolthe faces, or to provide for proper lubrication. This is achieved by installing the seals in a back-to-back or face-to-face configuration, as illustrated in Figures 3-12 and 3-13. For cooling andsolids/abrasives removal, fluid can be re-circulated from the product side or provided by anexternal source. In applications where the product has a relatively low vapor pressure, forexample, water or hydrocarbons, a barrier fluid with a higher vapor pressure is used to keep theproduct from vaporizing at the seal interface and to prevent the inboard seal from running dry. Ifthe product is toxic or harmful, a clean barrier fluid is introduced at a higher pressure tominimize toxin release. The outboard seal also provides a back-up in case of failure of theproduct seal.

Figure 3-12Back-to-Back Dual Seal



3-11

Figure 3-13Face-to-Face Dual Seal

Key Technical Point

Some applications require the use of multiple seals to provide for flushing orbarrier fluids, or pressure staging to deal with higher pressures. Flushing isused to remove contaminants, to cool the faces, or to provide for properlubrication. Selections include back-to-back, face-to-face doublearrangements, and a choice of buffer fluid or barrier fluid, depending uponapplication.

Pressure staging is accomplished by using multiple seals installed in series (shown in Figure3-14) so that the fluid pressure between any two cavities is limited to the maximum servicepressure limit of the mechanical face seal for the particular product fluid. Pressure stagingpermits isolating very high pressures that cannot be handled by a single mechanical face seal.Pressure staging usually requires the use of an intermediate fluid that is circulated to keep theseals cool. This is because stagnant fluid in the seal cavity is ineffective in removing the heatgenerated at the sealing interface, which can create hot pockets that cause the seal tomalfunction.

Figure 3-14Pressure Stage Tandem Seal



3-12

3.4 Seal Cartridges

Seal cartridges are pre-assembled mechanical face seal assemblies that contain all of the essentialcomponents. Cartridges are used to package mechanical face seals for ease of handling andinstallation. An example of a single seal cartridge is shown in Figure 3-15. In this arrangement,the primary ring and its associated devices are mounted on a sleeve temporarily attached to theenclosure that holds the mating ring. The assembly provides for proper spring loading and axialpositioning of the primary ring and mating ring. After the cartridge is mounted on the housingand the sleeve is secured to the shaft, the temporary attachment device holding the sleeve to themating ring enclosure is removed.

Figure 3-15Single Seal Cartridge

Cartridges can be provided with either rotating primary rings or stationary primary rings andwith single or multiple mechanical face seals. The schemes for assembling cartridges vary fromdesign to design.

Figure 3-16 shows a multi-stage balanced stator design seal cartridge assembly and Figure 3-17shows details of one of the stages. This seal design is one of the four alternative designscommonly used in a critical application (Main Coolant Pump) in U.S. nuclear power plants [35].

Key O&M Cost Point

Seal cartridges are pre-assembled mechanical face seal assemblies thatcontain all of the essential components. Cartridges are used to packagemechanical face seals for ease of handling and installation. Even thoughmaterial cost is higher, cartridges save money by simplifying maintenanceand eliminating installation related failures.



3-13

Figure 3-16Balanced Stator Design Multi-Seal Cartridge Supplied by a Manufacturer for a MainCoolant Pump [35]



3-14

Figure 3-17Seal Stage Details of a Balanced Stator Design Multi-Seal Cartridge Supplied by aManufacturer for a Main Coolant Pump [35]



3-15

3.5 Seal Chamber Design and Flushing

The seal chamber is sometimes referred to as the seal cavity or seal box. Figure 3-18 shows themost common variations in the seal chamber designs in centrifugal pumps. The seal chamber isthe cavity where the mechanical face seal resides and is often the same stuffing box chamber thatwas designed to house conventional soft packing. As such, the chamber provides only limitedvolume for the fluid to circulate naturally. Lack of circulation leads to hot spots in the face seal,and the stagnant cavity allows solids to settle. To overcome these space limitations, either analternative seal chamber design can be used or the seal chamber can be equipped with a means tocirculate fluid. Depending on the application, the circulated fluid can be the process fluid or anexternal fluid selected to provide better conditions in which the seal can operate, or to control therelease of contaminants.

Figure 3-18Common Variations in Seal Chamber Design



3-16

Based on research in seal chamber designs [7,48], it is now well established that enlarged sealchambers, and the use of tapered bore chambers, can dramatically lower fluid temperature andseal face temperatures. Wherever the envelope constraints in a given pump application permit,the seal chamber should be enlarged to improve the seal performance/life due to lowertemperatures and increased fluid circulation around the seal. The seal chamber design also playsa critical role in obtaining satisfactory performance from mechanical face seals handling abrasiveslurries.

Key Technical Point

Mechanical seals are often installed in the same cavity that is designed toaccept conventional packings. This limits the fluid circulation around theseal, leading to high seal temperatures and accumulation of solids. Anenlarged seal chamber with tapered bore can dramatically improve fluidcirculation, lowering seal temperature and eliminating accumulation ofsolids.

In addition to the chamber design, seal flushing is dictated by application requirements in manycases to achieve satisfactory performance. API Standard 682 describes 17 plans to flush the sealchamber [8]. Selection of the type of plan needed will depend on the process fluid and operatingtemperature. Fluids having high vapor pressures (for example, hot water, light hydrocarbons,etc.), high temperature, containing abrasives (for example, service water, slurries, etc.), orcontaining dissolved solids (for example, borated water) are common mechanical sealapplication problems that can benefit from flushing.

The most common API Standard 682 flush plans used with clean process fluids are Plan 11 andPlan 21. Plan 11 is illustrated in Figure 3-19. To control the amount of fluid re-circulated, athrottle bushing is incorporated inboard of the mechanical face seal and a control orifice isinstalled in the flush line. Flow enters the seal chamber adjacent to the mechanical face seal,flushes the faces, and flows across the seal back into the pump. Plan 21 is similar to Plan 11except that a cooler is installed in the flush line in series with the control orifice. Forcontaminated process fluids, strainers/filters can be added to clean the flush fluid.

Figure 3-19A Typical Flush Plan for a Cooling Seal Chamber



3-17

3.5.1 Seal Arrangements for Abrasive Applications

Abrasives will generally cause rapid wear of the faces while excessive heat from the pumpedfluid, or as a result of seal friction, will damage the elastomers and distort seal components,causing the seal to leak and fail [49,50,51,55]. The seal should be provided with a clean,relatively cool, abrasive-free flush to lubricate and remove the heat generated by the seal facesand to prevent flashing at the seal faces. A clean liquid from an outside source can be used.However, the resulting contamination of the pumped product by an external source might makethis type of flush undesirable. For this reason, a re-circulated or bypass fluid from the liquidbeing pumped is frequently used. If necessary, this re-circulated flush fluid can be cooled andany abrasive particles removed before it is injected into the seal. When multiple seals, as shownin Figures 3-12, 3-13, or 3-14, are used, a combination of internal and/or external seal flusharrangements can be used.

In severe abrasive duty applications (for example, clinker grinder in fossil plants and abrasiveslurry handling pumps), mechanical face seals have a history of unreliable performance and shortlife, even when flushing arrangements are used [50, 51]. This is due to the fact that, in addition toexposure to harsh abrasive particles, seals are exposed to large shaft deflections (both static anddynamic), frequent starts/stops, transients, shock, and vibration, which exceed the capabilities offace seals. Similar sealing problems in downhole drilling applications have been solved by analternative elastomeric seal design employing hydrodynamic lubrication [52, 53, 54]. This designmight be a potential solution to the fossil plant slurry handling equipment and sealing problemswhere application conditions are unsuitable for mechanical face seals.

3.6 Closing Force

In order for the face seal to function properly, a certain amount of face load is required. Faceloading is developed by the energizing springs and by the process of pressure acting on theunbalanced area of the seal. The closing force is the sum of the spring load plus the fluidpressure, multiplied by the unbalanced area, and is expressed as:

Fclosing = Spring (Fs) + Hydraulic closing force (Fh)= Fs + Af ('P x B + P2)

Where,

'P = Pressure drop (P1-P2)Af = Face areaB = Balance ratioP1 = Upstream pressureP2 = Downstream pressureFclosing = Closing forceFs = Spring forceFh = Hydraulic force



3-18

The total closing force, Fclosing, is supported primarily by the fluid film pressure (p) between theseal faces, and the residual force is supported by mechanical asperity contact (pm) between thefaces:

Fclosing = k p Af + pm Af

In this equation, k is a factor that can vary between zero and 1.0, depending upon the actualpressure distribution across the face.

k = 0.5 for linear pressure distribution> 0.5 for convex pressure distribution,< 0.5 for concave pressure distribution

The value of k depends upon whether the faces are parallel convergent or divergent (Figure 4-3)as further discussed in Section 4.4.4.

3.6.1 Balance Ratio

Mechanical face seals can be of an unbalanced design, a fully balanced design, or partiallybalanced design to reduce the face loading due to hydraulic pressure, as shown in Figure 3-20.The term balanced refers to the case where B < 1.0, or where the average pressure load on theface is less than the sealed pressure. Most mechanical face seals have a balance ratio between0.65 to 0.85. This range provides reduced face loading while maintaining stability. The seal canbecome hydraulically unstable or the seal faces can separate under pressure fluctuations if thebalance ratio becomes less than 0.65. Seals with a balance ratio greater than 1.0 are termedunbalanced, that is, these seals have an average pressure load on the face that is greater than thesealed pressure. While most seals that operate at high pressure are of the balanced type, manylow-pressure seals operate at B > 1.0 because of the convenience of design.



3-19

Figure 3-20Unbalanced, Balanced, and Partially Balanced Seal Designs



3-20

Key Technical Point

Mechanical face seals can be unbalanced, fully balanced, or partiallybalanced to reduce the face loading due to hydraulic pressure. The termbalanced refers to the case where the average pressure load on the face is lessthan the sealed pressure. Most mechanical face seals have a balance ratiobetween 0.65 to 0.85. This range provides reduced face loading withoutpotential concern of face parting.

The term balance ratio is used to describe the fraction of the fluid pressure that is acting to closethe seal faces. It is defined as the ratio of hydraulic loading area to the seal interface area. If abellows seal is used, the effective sealing diameter must be calculated. Balance ratios arecalculated as follows.

For externally pressurized seals:

� ��

� �� 2

i2o

2b

2o

2i

2o

2b

2o

eD D

D D

D D /4

D D /4 B

�

�

�S

�S

For internally pressurized seals:

� ��

� �� 2

i2o

2i

2b

2i

2o

2i

2b

iD D

D D

D D /4

D D /4 B

�

�

�S

�S

For bellows seals, the mean diameter can be used or, alternatively, diameter Dsb is substituted fordiameter Db:

� �2

D D D

2bi

2bosb

�

WhereB = Balance ratio (Be or Bi)Be = Balance ratio for externally pressurized sealsBi = Balance ratio for internally pressurized sealsDo = Outside interface diameterDi = Inside interface diameterDb = Balance diameterDsb = Effective sealing diameter for bellows sealsDbo = Outside diameter of bellowsDbi = Inside diameter of bellows



3-21

3.6.2 Pressure Distribution Between the Sealing Faces

In any standard seal design configuration, the hydraulic pressure acts across the seal interfaceeither from the OD to the ID or vice versa. In either case, the fluid film pressure between thefaces at the point of action is a maximum that is reduced across the interface to the pressure onthe downstream side at the opposite side of the contact area.

Although several theories have been advanced that define the pressure gradient across the facesas being either linear, concave, or convex, no one theory has gained general recognition. In fact,the pressure gradient varies during operation due to seal wear and deflections caused by pressureand temperature changes. Whatever the true pressure gradient across the face might be, the filmpressure tends to separate the contact faces of the primary seal rings, opposing the closing forcesdue to the mechanical spring load and the hydraulic pressures acting on the unbalanced area ofthe seal. However, in most mechanical seal designs, the resultant force from the film pressuredoes not completely balance the closing forces and the small residual force is supported by themechanical contact of the asperities on the faces.

Key Technical Point

Pressure distribution across the seal face width can be linear, concave, orconvex and it can change with variations in pressure, temperature, and sealwear. This can affect seal performance (leakage, torque, temperature)during operation.

Figure 3-21 shows how the closing force due to spring pressure and hydraulic imbalance is inequilibrium with the pressure. Based on a linearly varying pressure gradient, the seal would be100 percent balanced when the hydraulic area is one-half the face area. Making the hydraulicarea less than half the seal face area would then cause the hydraulic pressure to separate the facesin the absence of spring force.

Figure 3-21Face Pressure Distribution Due to Hydraulic Pressure and Spring Force



3-22

3.6.3 Stationary Versus Rotating Seal Balance

The balance ratio can be affected by the way the pressure area is defined. The same balance ratiocan be achieved by two different primary ring and mating ring geometries, depending uponwhich one of the two faces is the narrower face.

If the stationary ring (mating ring) defines the pressure area, as shown in Figure 3-22(a), the faceload due to pressure can vary around the circumference if the mating ring is offset radially withrespect to the primary ring. The differential pressure area defined by the diameter Do on themating ring and the shaft diameter Db would be maximum in the direction of the offset andminimum on the opposite side. This circumferential variation in the seal face load exertsmoments on the seal faces that can cause vibrations and instability, and affect seal performance.This problem can be eliminated by defining the differential pressure area using the face of therotating member as shown in Figure 3-22(b). Additional considerations related to primary andsecondary seal wear when selecting a rotating balance or stationary balance design are discussedin Section 4.4.6.

Figure 3-22Rotating Seal Balance Designs



3-23

3.7 Pressure Velocity (PV) Parameter and Limit

The measure of a seal to provide useful service is defined by its PV parameter that, like Journalbearings, is the product of the pressure and the sliding velocity. Two ways are used to define thePV parameter. The first method uses differential pressure multiplied by the average slidingvelocity, and the second method uses net face pressure multiplied by the average sliding velocity.The more common method used by mechanical face seal manufacturers and users to rate the PVparameter, is the differential pressure drop method because it can be easily related to sealoperating pressure and balance ratio does not need to be known.

Table 3-4 provides the PV values (based on differential pressure approach) for materialscommonly used in both unbalanced and balanced mechanical face seals.

In general, the unbalanced seal design is simpler and less costly, and is the preferred choice if itsatisfies the PV limits for a given application. The balanced seal design permits operation underhigher pressure and speed combinations but it requires a stepped shaft or stepped sleevearrangement, which is generally more expensive. If the fluid is clean (free of abrasives/solidparticles) and is compatible with the carbon material, the carbon versus the appropriate hardermaterial combination should be selected. For non-clean fluids, both seal faces need to be hard toprovide satisfactory wear life.

Table 3-4Approximate PV Limits psi-ft/min (Mpa-m/sec) for General Seals with VariousCombinations of Seal Face Materials and Fluids

Water and Aqueous Liquids Other Liquids

Face MaterialCombination Unbalanced Balanced Unbalanced Balanced

Carbon vs.

x Stainless steel 1.45 x 104 (0.5) 1.45x 103 (3)

x Lead bronze 7.23 x 104 (2.5) 1.01 x 105 (3.5)

x Stellite 7.23 x104 (2.5) 2.46 x 105 (8.6) 1.45 x 105 (5) 1.68 x 106 (59)

x Alumina 1.01 x 105 (3.5) 6.08 x 105 (21) 2.60 x 105 (9) 1.22 x 106 (43)

x Chrome oxide 2.03 x 105 (7) 1.22 x 106 (43)

x Tungsten carbide 2.03 x 105 (7) 1.22 x 106 (43) 2.60 x 105 (9) 3.53 x 106 (124)

x Silicon carbide 2.60 x 105 (9) 1.82 x 106 (64) 2.60 x 105 (9) 5.35 x 106 (188)

Tungsten carbide vs.

x Tungsten carbide 1.30E+105 (4.6) 7.52 x 105 (26) 2.03 x 105 (7) 1.22 x 106 (43)

x Silicon carbide 1.74E+105 (6) 1.04 x 106 (36) 2.60 x 105 (9) 3.04 x 106 (106)



3-24

3.8 Temperature Considerations and ''T Limit

For a mechanical seal to function reliably, a fluid film needs to be maintained between the sealfaces. Operation of the seal results in frictional heat generation at the sealing interface, whichlowers the fluid viscosity and the load carrying capacity of the liquid film. The load bearingcapacity can decrease sufficiently and result in heavy contact between the seal face, causingsevere wear or face damage. The frictional heat can also raise the temperature of the liquid filmat the sealing interface to such an extent that fluid instantaneously changes its phase from liquidto gaseous under the pressure that is present on the low-pressure side of the seal. This phasechange often causes an intermittent banging or popping sound and results in severe face damageand excessive leakage.

During seal operation, it is necessary that a stable liquid film be maintained, considering theanticipated increase in temperature ('T) due to the seal friction over the bulk fluid temperature.Figure 3-23 shows how pressure and temperature affect the boiling point of a liquid, and the 'Tmargin that needs to be maintained between the bulk fluid temperature and the boiling pointcurve to accommodate the increase in fluid temperature at the sealing interface without causingvaporization. This figure also shows the operating envelope for seal performance defined by thepressure/temperature limits (including the 'T margin), as well as the PV limit.

Cooling of the seal chamber (for example, by using one of the flushing arrangements describedin Section 3.5) protects against boiling of the fluid, as does an increase in the chamber pressureabove the vapor pressure. The most suitable approach to suppress boiling and ensure adequate'T margin below the limit depends upon the application. Technical performance data regardingthe 'T margin should be obtained from seal manufacturers to evaluate and ensure reliableoperation in a given application.

Key Technical Point

For satisfactory performance, the seal design and material selections shouldsatisfy the PV limit and the ''T limit under all operating conditions to ensurethat fluid film is maintained between the seal faces. Loss of film can lead toimmediate seizure and seal failure.



3-25

Figure 3-23Pressure/Temperature Operating Envelope Showing ''T Margin Required for SealOperation

3.9 Improved Seal Face Designs

A fundamental requirement for a mechanical face seal to function reliably is that the faces beseparated by a thin fluid film during operation. In practice, a small amount of asperity contactbetween the faces occurs in most applications, causing a small amount of wear that determinesseal life but does not affect seal performance. Under high pressure and high temperaturecombinations, the film thickness decreases and the asperity contact between the faces increases,which in turn increases seal friction and heat (see Section 4.4.1 for further discussion). Thislimits the pressure, temperature, and speed performance envelope, as well as, reliability of theconventional flat face mechanical seals. The problem becomes especially severe when sealinghot water and other low lubricity fluids [21-34].

One approach that has proven to be successful for sealing hot water under high pressure and highspeeds, as well as for sealing other high-volatility, low-lubricity fluids, is the use of seal facedesigns that have positive hydrodynamic lubrication features. Figure 3-24 is the first design thatbecame commercially successful and is widely used in critical hot water sealing applications(including Main Coolant Pumps) in many European nuclear power plants and some U.S. nuclearpower plants [3]. In this design, the cooling notches or thermal hydrodynamic grooves introducecircumferential waviness of the seal face due to variations in the temperature around the sealcircumference.



3-26

Figure 3-24Seal Face with Thermal Hydrodynamic Grooves for Positive Hydrodynamic Lubrication [3]

The circumferential waviness in conjunction with the relative rotational velocity between thefaces introduces a strong hydrodynamic action, higher film pressures, and a thicker film. This isthe fundamental mechanism responsible for extending the performance envelope of the sealswith hydrodynamic grooves on the seal face. It should be noted that the higher pressure andspeed capabilities are achieved at the cost of increased leakage and vulnerability of the seal toingest debris and unfiltered solid particulates in the fluid. The manufacturer of the specific sealdesign being considered should be consulted for their recommendations and their experience insimilar applications. Prototype qualification testing is strongly recommended for critical serviceapplications.

As shown in Figure 3-25, the hydrodynamic grooves can be incorporated on the seal face to pickup fluid from either the outer or the inner periphery, depending upon the applicationrequirements. Figure 3-26 shows several other variations of this basic approach to enhance thelubrication between the seal faces.



3-27

Figure 3-25Design Options with Hydrodynamic Grooves on the Outer Periphery or Inner Periphery ofSeal Face

Figure 3-26Other Variations in Seal Face Geometry to Enhance Lubrication of the Faces



3-28

Several alternative designs that also maintain a full hydrodynamic film lubrication under highduty application conditions (including transients) have been reported over the years since thesuccessful commercial introduction of the design shown in Figure 3-24. These include eccentricseals for nuclear pumps, optimized grooves face seals, Rayleigh-step floating-ring seals, moving-wave mechanical face seals, and polymer seal rings sliding against silicone carbide [37-41, 47].

Key Technical Point

Seal designs with special features to enhance lubrication at the sealinginterface (for example, hydrodynamic grooves, recesses, or laser-texturedsurfaces) can extend the pressure, speed, and temperature limits. The trade-off (for example, higher leakage rate versus increased reliability undertransient conditions) should be carefully evaluated during seal selection.

Research in recent years has shown that the newest technology, laser-textured surface designs,are capable of providing the full film lubrication (and therefore long life) without the penalty ofexcessive leakage associated with the earlier hydrodynamic film seal designs. These includelaser-faced entry and return-flow recesses, laser-textured faces with micro-pores that serve asmicro-hydrodynamic bearings [42-46]. One of these laser-textured surface designs that hasemerged as a promising and commercially viable design was recently introduced by a sealmanufacturer [46].

3.10 Hydrostatic Seal Design

The hydrostatic seal design is a non-contacting mechanical face seal that permits some controlledflow rate to pass between the faces. As illustrated in Figure 3-27, the seals are designed with aconverging taper on the faces to balance the pressure distribution between the back of the sealring and the seal face. Under no-pressure conditions, the seal faces can come into contact andcause dry running during startup. To prevent dry running, the seal requires that some pressure beapplied to the tapered side prior to rotation. The initial pressure ensures that minimum leakagedevelops and that the seal faces will not contact during startup. Because no rubbing contactoccurs in this type of seal, there is virtually no wear. In the Westinghouse configurations used inMain Coolant Pumps, the tapered seal faces are designed to permit a minimum leakage of 0.2gallons per minute (10 milliliters per second) during startup conditions and a nominal leakage of3.0 gallons per minute (190 milliliters per second) during normal operation. Filtered sealinjection is used to keep particulates from entering the seal cavity.

Key Technical Point

The hydrostatic seal design is a non-contacting mechanical face seal thatpermits some controlled flow rate to pass between the faces. To prevent dryrunning, the seal requires that some pressure be applied to the tapered sideprior to rotation.



3-29

In some applications, conventional mechanical face seals contain the leakage past the hydrostaticseal. In this tandem configuration, most of the pressure breakdown occurs as leakage crosses thehydrostatic seal, and the remaining pressure drop is taken across the conventional mechanicalface seal. Under normal operation, the mechanical face seal is exposed to a significantly lowerpressure drop than the hydrostatic seal. It is typically designed as a backup to the hydrostatic sealto permit a safe shutdown of the system under higher pressure drop, should the hydrostatic sealfail.

Hydrostatic seals are available in either a rotating balance design or a stationary balance design.A detailed description of these designs, used in conjunction with hydrodynamic seals, isprovided in NMAC TR-100855, Main Coolant Pump Seal Maintenance Guide [35].

Figure 3-27Hydrostatic Face Seal Design


4-1

4 FAILURE MODES AND FUNDAMENTAL MECHANISMS

4.1 Introduction

The purpose of this section is to describe the failure modes of mechanical face seals and thefundamental mechanisms that are responsible for the failures. A significant amount of researchby seal manufacturers, universities, independent research organizations, national laboratories,and seal users has continued over the last four decades to improve fundamental understanding ofthe mechanisms that cause seal failure, which in turn has led to improvements in design, theselection of an appropriate design for each application, and guidance for installation andmaintenance [3, 7, 9, 34, 36].

Industry-specific data were gathered under this project by conducting a utility survey todetermine the most common failure modes in the nuclear and fossil power applications. Analyseswere then performed to determine all of the significant seal failure mechanisms that aredescribed in this section.

4.2 Definition of Seal Failure

The eventual failure mode of all mechanical face seals is leakage that is considered unacceptablefor the seal design/configuration being used. Excessive leakage can cause unacceptable loss offluid, reduction of pressure, or contamination of the system fluid by the barrier fluid in double-seal installations.

Seal leakage can occur for a variety of reasons and might result from failure at any of severalleak paths. The possible leak paths in a typical mechanical face seal are (see Figures 3-1 and 3-15 for reference):

x Between the seal faces

x Between the secondary seal and the primary ring

x Between the secondary seal and the mating ring

x At the secondary seal in the sleeve (in seal designs employing sleeves)

x At the secondary seal at the gland plate

While mechanical seal faces require some small level of leakage to function properly, the extentof leakage above this minimum requirement can be from a few drops to a continuous drip. Undernormal performance, typical leakage rates from mechanical face seals are in the range of afraction of ml/hr to a few ml/hr, depending upon seal size, fluid viscosity, pressure, temperature,


Failure Modes and Fundamental Mechanisms

4-2

and speed. There are no general quantitative criteria for what constitutes seal failure due toexcessive leakage.

The level of permissible leakage is dependent upon the operating requirements, environmentaland safety considerations, and economic considerations. In most clean water systems, quite highleakage rates are often tolerated as long as other functions of the operation are not affected. Ingeneral, most premature leakage problems result from improper selection of the seal design andmaterials, improper use of the seal, and improper installation.

Key Technical Point

The eventual failure mode of all mechanical face seals is leakage that isconsidered unacceptable for the seal design/configuration being used.Excessive leakage can cause unacceptable loss of fluid, reduction of pressure,or contamination of the system fluid by the barrier fluid in double sealinstallations. The level of acceptable leakage is dependent upon theapplication.

4.3 Industry Survey

Under this EPRI project, an industry survey was conducted to determine the most commonfailure modes for mechanical seals encountered in the nuclear and fossil power plantapplications. A survey questionnaire was sent to all EPRI NMAC and FMAC utility members,both domestic and international. The nuclear utilities included both BWR and PWR plants.Appendix A includes a complete copy of the questionnaire. In addition to the survey results,technical information from many other industry sources was used to identify the most commonfailure modes and mechanisms responsible for the failures. Based on the above, the followingappear to be the most problematical mechanical seal applications:

x Multi-stage centrifugal charging pumps

x Start-up feedwater pumps

x Condensate booster pumps

x Station heat pumps

x Pumps with mini-flow operation

x Pumps with variable flow requirements

x Boric acid system pumps with heat trace lines

This list does not include the main coolant pump seals, which, due to their higher importance,have already been addressed separately in NMAC TR-100855, Main Coolant Pump SealMaintenance Guide [35].



4-3

It should be noted that the only European nuclear power utility that responded reported noproblematical applications. It is conjectured that, like most other European utilities, they areusing mechanical seal designs with special features (for example, thermal hydrodynamic groovesor notches on the seal faces as described in Section 3.9) to provide enhanced seal facelubrication.

A common denominator in all of these applications is sealing of hot water, which is a low-lubricity/high-volatility liquid that is difficult to seal, especially when high fluid pressures areencountered [21-25]. The problem applications also include operation off the Best EfficiencyPoint (mini-flow operation, variable flow requirements) and dissolved solids that can crystallize(boric acid application).

The most commonly cited reasons (not root causes) for mechanical seal problems encountered atthe plants surveyed were:

x Improper installation

x Improper seal face compression

x Dirty or abrasive fluids

x Differences between normal operating conditions and design conditions

x Excessive axial or radial movement caused by off Best Efficiency Point operation cavitation,out of balance, bent shaft, misalignment, and bad bearings

x Equipment operating conditions not completely defined

x Improper design and face seal material selected for the application

x Pressure and/or temperature transients due to variable system operation

x Lack of training

4.4 Fundamental Failure Mechanisms

Successful operation of mechanical seals depends upon the development of a thin film of fluid[typically less than 40 micro-inches (1 Pm)] that separates the seal faces during operation, thuskeeping the seal wear to a minimum and providing long life [1-6]. It is now well accepted thatthe fundamental mechanism responsible for generating a fluid film during operation ofmechanical seals is hydrodynamic lubrication caused by unavoidable geometrical imperfections,especially waviness of seal faces in the circumferential direction [5,7]. The amount of wavinessrequired to generate hydrodynamic film pressures and keep the faces apart is small, less than 40micro-inches (1 Pm), and can be caused by manufacturing imperfections, local mechanicaldistortions due to drive pins/anti-rotation mechanisms, thermal distortions due to non-uniformcontact pressure, and wear of the faces during operation.



4-4

To function properly, mechanical seals must maintain a fluid film to provide lubrication, preventdirect rubbing contact, and provide cooling of the seal faces under all operating conditions. Sealfailures occur when the film thickness and the film pressure between the seal faces change andbecome unacceptably low or unacceptably high. This either leads to excessive friction, wear, andheat, causing damage to the seal faces and other seal hardware, or leads to parting of the sealfaces. The eventual seal failure mode in both cases is high leakage.

The fundamental mechanisms most commonly responsible for seal failures are described below.

4.4.1 PV Limits Exceeded

As discussed in Section 3.7, the face loading of the seal faces is dependent upon whether the sealis a balanced or unbalanced design, the degree of balance, the spring force, and the fluid pressurebeing sealed. For optimum life, the film thickness should be sufficient to completely eliminateasperity contact between the seal faces. As the fluid pressure increases, the film thicknessbetween the seal faces decreases, transitioning from full film lubrication to mixed lubrication,and in extreme cases, to boundary lubrication (Figure 4-1).

Under full film operation, all of the seal face load is carried by the fluid pressure generated byhydrodynamic action. Under mixed lubrication, the fluid film pressure still carries a majority ofthe seal face load; however, the solid contact between the asperities of the mating seal facescarries part of the load. Under a boundary lubrication regime, practically the entire load is carriedby direct solid contact and the fluid film carries a negligible amount of the total load.

When the asperity contact does occur but is not extensive (as in mixed lubrication), seal life isgoverned by the wear of the face materials. Seal life can vary from several months to over 3 to 4years, depending upon the application conditions. When asperity contact becomes extensive, asin boundary lubrication, the seal frictional heat leads to immediate failure. Adverse thermalstress conditions can result from higher pressures as well as from inadequate heat dissipation,and can cause heat checking of the seal faces.



4-5

Figure 4-1Lubrication Regimes at Seal Interface Showing AsperityContact as Lubrication Changes from Full Film to Mixed to Boundary

For higher pressures, balanced seals provide the best performance because they reduce the faceloads and the asperity contact. However, as the balance ratio is decreased to handle higherpressures, the vulnerability of the seal to parting of the seal faces under fluid pressure/temperature transients increases. Balance ratios of 0.62 or less should be avoided to prevent faceparting. The PV limits for both balanced and unbalanced seals for all commonly used materialsare provided in Table 3-4.

Key Technical Point

For satisfactory performance, the seal design and material selections shouldsatisfy the PV limit and the ''T limit under all operating conditions to ensurethat fluid film is maintained between the seal faces. Loss of film can lead toimmediate seizure and seal failure.

4.4.2 ''T Limits Exceeded, Causing Film Vaporization/Collapse

This is one of the most common causes of seal failure in high pressure, hot water pumps. Asdiscussed in Sections 3.7 and 3.8, sealing of low-lubricity/high-volatility fluids (for example,water, glycol, and light hydrocarbons) is difficult, particularly under higher pressure and speedcombinations. If under given operating conditions the liquid film at the seal interface vaporizes,dry rubbing of the seal faces occurs, leading to excessive heat, seal popping, and failure.



4-6

Figure 3-23 in Section 3 shows the 'T margin that needs to be maintained between the bulk fluidtemperature and the boiling point curve of the fluid being sealed to accommodate the increase influid temperature at the sealing interface without vaporization. Both the PV limits and the 'Tmargins are frequently challenged and must be respected for successful operation of face seals inhigh pressure, low-lubricity/high-volatility fluid applications. Increasing the chamber pressureand/or cooling to suppress fluid vaporization can improve seal performance.

Approaches discussed in Section 3.9 to improve lubrication of the seal faces can be used toextend the PV and 'T limits of mechanical seals in many applications.

4.4.3 Inadequate Cooling

Many mechanical seal chamber dimensions in pumps are based on interchangeability withstuffing box packing arrangement. Often this imposes severe restrictions on the seal design, thuslimiting the structural strength of and heat transfer from the seal to the process fluid. The narrowradial clearances between the seal boundary and the seal chamber limits flow of the high-temperature fluid surrounding the seal, resulting in unacceptable thermal distortions and coningof the seal faces. In such cases, isolated pockets of hot fluid in the vicinity of the seal can reachtemperatures that are several hundred degrees higher than the process fluid. Excessive coningdue to high differential temperatures is often responsible for seal failure as described in Section4.4.4.

As described in Section 3.5, increasing the radial clearance at the seal outside diameter, usingenlarged and/or tapered seal chamber designs, incorporating a seal flushing arrangement, orincreasing the flow rate of the flushing fluid can significantly reduce the seal temperature. Thiscan provide a dramatic improvement in the performance of the seal in such installations.

Key Technical Point

Mechanical seals are often installed in the same cavity that is designed toaccept conventional packings. This limits the fluid circulation around theseal, leading to high seal temperatures and accumulation of solids. Anenlarged seal chamber with tapered bore can dramatically improve fluidcirculation, lowering seal temperature and eliminating accumulation ofsolids.

4.4.4 Transients Causing Excessive Seal Face Coning

Thermal stresses and pressures cause deflections of the seal faces (coning) that change theinitially parallel fluid film gap between the seal faces to either a convergent or a divergent gap(Figure 4-2). By design, the distortion of the seal faces caused by coning should be limited toless than 40 micro-inches (1 Pm), which is the typical film thickness between the seal faces.



4-7

Figure 4-2Extremes of Seal Face Distortion (Coning) Due to Thermal and Pressure Effects

A frequent cause of seal failure is coning of seal faces that results in heavy contact at the insidediameter of seal faces during operation (positive coning). Positive coning is caused by thermaldistortions due to seal friction and inadequate cooling. Positive coning, if excessive, changes thelubrication regime from full film to mixed or boundary lubrication. This, in turn, increasesfriction and interfacial temperature and causes rapid wear of the seal faces. Positive coningchanges the interfacial film pressure distribution from linear in a parallel face situation to convexor concave pressure distribution, depending upon whether the seal is pressurized on the inside orthe outside diameter. Figure 4-3 shows the changes in pressure distribution for an outsidepressurized seal.

Key Technical Point

Thermal distortions of seal faces due to operational transients can causepositive coning (contact on ID) or negative coning (contact on OD) of the sealfaces. Coning in excess of film thickness can cause film rupture seizure orface parting, resulting in a large increase in leakage.

In extreme cases of positive coning with inside pressurization, fluid leakage past the sealingfaces is completely cut off, thus leading to total collapse of the fluid film and immediate failure.In the case of outside pressurization, the increase in film pressure can cause parting of the sealfaces.



4-8

Figure 4-3Pressure Distribution Changes Caused by Coning of the Seal Faces (for OutsidePressurized Seal)

Another cause of seal failure is coning of seal faces that results in contact at the outside diameterof seal faces (negative coning). Negative coning is caused by seal distortion due to pressures,including transients, exceeding acceptable limits. Negative coning causes the pressuredistribution between the seal faces to change sufficiently to either overcome the seal closingforce, thus causing parting of the seal faces and very high leakage, or to reduce the filmthickness, resulting in mixed/boundary lubrication.

Key Technical Point

Pressure distribution across the seal faces is affected by seal face coning dueto changes in pressure and speed as well as the wear-in process. Excessiveconing causes seal failure either due to seizure or face parting. Hard faceversus soft face material combinations are more tolerant of coning than ifboth faces are hard.



4-9

In fact, the coning and the wear-in process have complex interactions on seal performance,depending upon the sequence of events (Figures 4-4 and 4-5). The performance is also affectedby the ability of one of the faces to wear-in rapidly without causing immediate seal failure (forexample, in the case of a carbon face) or by whether both the seal faces are too hard to wear-inrapidly (for example, silicone carbide, tungsten carbide).

Figure 4-4Changes in Seal Contact Area Under Constant Operating Conditions During the Wear-InProcess for a Seal With a Hard Face and a Soft Face

Figure 4-5Example of a Wear-In Sequence (Stages 1 through 4) for a Mechanical Seal with a Soft SealFace

4.4.5 Operation Away from Best Efficiency Point

Large shaft deflections in pumps due to operation far away from the best efficiency point cancause misalignment and eccentricity between the seal faces during operation. Extensiveanalytical and experimental research sponsored by NASA has led to a good understanding ofhow rotor/stator eccentricity and angular misalignment of the faces can create a strong pumpingaction across the seal faces, over and beyond the hydrodynamic action caused by normalcircumferential waviness [5].



4-10

In applications where fluid is present on only one side of the seal, eccentricity can cause highexternal leakage. In applications where fluid is present on both sides of the seal (for example, ina double seal arrangement with buffer fluid), a high rate of fluid transfer can occur eitheroutwardly (from high-pressure to low-pressure side) or inwardly (from low-pressure to high-pressure side). The fluid flow by this mechanism from low-pressure to high-pressure side iscalled inward pumping. Inward pumping can cause significant mixing of the fluids. Whenabrasives are present in one of the fluids, inward pumping causes high abrasive wear of the sealfaces. These effects can be minimized by controlling the misalignments and eccentricities to anacceptably low level.

Key Technical Point

Operation away from Best Efficiency Point (BEP) is a frequent cause ofshort seal life/seal failures. Off BEP conditions cause large shaft deflectionsand vibrations resulting in premature degradation of mechanical seals.

It is also important to note that the pumping action in a misaligned, eccentric face seal causes thefluid to transfer across the seal interface if the wide seal face is rotating as shown in Figure4-6(a). Fluid transfer can accelerate abrasive wear of the seal faces, especially in applicationswhere one fluid has solid particulates, for example, service water applications. The effect can beminimized by selecting a seal design in which the narrow face is the rotating element, as shownin Figure 4-6(b).



4-11

Figure 4-6Fluid Pumping Action Across the Seal Faces Due to Static Offset and Misalignment



4-12

4.4.6 Seal Misalignment/Premature Degradation of Primary and Secondary Seals

Mechanical face seal misalignment occurs in all installations, but the severity of themisalignment and the manner in which it is accommodated dictates whether the mechanical faceseal will perform satisfactorily in service. Misalignment can be caused by runout of the shaft orface seal due to manufacturing clearances and tolerances or by deflection of the mountingsurfaces due to load or temperature. It can be classified in two categories: static misalignment ordynamic misalignment. Both static and dynamic misalignment can reduce the service life of themechanical face seal by premature degradation of the primary or secondary seals.

Static Misalignment: Static misalignment is the condition in which the seal faces run in aneccentric position relative to each other. They remain in that position unless a change inoperating conditions upsets their relative positions. The effect of static misalignment is a weartrack on the wider face that is offset from its concentric position. If the misalignment remainsconstant (within limits) after installation, the primary seal faces should function properly andprovide normal service life. If the misalignment is the result of load, such as shaft tilt due to sideloading as shown in Figure 4-7, then the mechanical face seal will operate satisfactorily until theload is changed. Once the load is changed, a new wear track will need to develop before themating seal faces again begin to function normally. This condition becomes more severe whenthe wider face is made of relatively soft material that permits a relatively deep wear track todevelop. In most cases, a deep wear track causes face leakage under both static and runningconditions.

Figure 4-7Rotating Balance Seal Wobble Caused by Shaft Tilt



4-13

Key Technical Point

Static and dynamic misalignment between seal faces can cause strong fluidpumping action across the faces causing either inward pumping or outwardpumping of the product fluid and/or buffer fluid. Leakages under misalignedconditions can be several times the normal leak rate.

Static misalignment can also create a condition called pumping-in or pumping-out of the fluidwhen the rotating face is wider than the stationary face, as already described in Section 4.4.5 andillustrated in Figure 4-6. Pumping is caused by the radial velocity vector that forces fluid in andout of the narrower seal face. This radial vector can be large enough to pump fluid from the low-pressure side to the higher-pressure side. Pumping-in is particularly harmful when the low-pressure side has contaminants. Pumping-out does not usually damage the seal, but onlyincreases the leak rate. As stated earlier, the pumping phenomenon due to static offset can beeliminated by making the rotating face narrower and selecting the softer face material for thenarrower face.

Static misalignment due to shaft tilt also creates an axial sliding action at the secondary seallocation, as shown in Figure 4-7. Premature degradation of the secondary seal area due tofretting/wear can cause seal problems.

Dynamic Misalignment: Dynamic misalignment exists when the mechanical face seals have torespond to changes with each revolution. Shaft tilt creates a condition where the seal has torespond dynamically to the change in axial position of the mechanical face seal with everyrevolution of the shaft. Shaft tilt can create premature failure of the secondary seal and cansignificantly affect the integrity of the sealing faces. When the secondary seal slides toaccommodate shaft tilt (shown in Figure 4-7), it axially sweeps the shaft with each revolution ofthe shaft and causes the secondary seal and its mating surface to wear. Excessive leakage,especially at high speeds, can also develop if the seal faces cannot dynamically respond torelative axial movement to maintain face contact. Leakage due to shaft tilt can also occur atrelatively low speeds if the spring load or pressure do not generate enough face loading,especially when the inside diameter of the seal is pressurized. Problems associated with shaft tiltcan be reduced or eliminated by allowing the stationary ring to pivot as shown in Figure 4-8.

Key Technical Point

Premature wear of the primary sealing faces and secondary seals, causingexcessive leakage when stationary and when running, are also commonsymptoms of excessive misalignment.



4-14

Figure 4-8Shaft Tilt Accommodated by Stationary Ring Pivot

Problems caused by dynamic misalignment also occur when the rotating seal face axis is offsetfrom the rotation axis of the shaft. Under this condition, the rotating seal face radially sweeps thestationary face once every revolution as shown in Figure 4-9. This condition exists to someextent in all seals, however, leakage and wear become a problem only when the runout isexcessive and the rotating face is narrower than the stationary face. If the narrower rotating faceturns with an offset around the axis of revolution, a radial vector is generated that pumps fluid inand out of the narrow face. The problem becomes severe when the product or environmentcontains abrasives that can be forced between the sealing faces. Leakage due to runout is usuallypresent only during running conditions unless the sealing faces have been damaged.



4-15

Figure 4-9Seal Pumping Caused by Dynamic Offset of Rotating Narrow Face

Problems associated with dynamic offset are more common when the primary face (which hasmore components and more potential for imbalance) rotates rather than when the mating ringrotates. Offset problems can also be caused by excessive clearances in the assembly or improperinstallation. The problem can usually be eliminated by selecting a seal configuration with arotating mating ring, which can be manufactured to much tighter tolerances to minimizeclearances and imbalance.

4.4.7 Excessive Out-of-Flatness (Warpage) During Operation

Key Technical Point

Mechanical face seals are precision components, requiring the sealing facesto be flat, typically within one light band (11.6 x 10-6 inches) across one-inchwidth. Too much out-of-flatness can lead to excessive seal leakage.

For proper operation without excessive leakage, manufacturers control seal flatness to typicallywithin one light-band per lineal inch. In some cases, the flatness of the seal faces can changeconsiderably during operation due to wear, misalignment, and exposure to high temperatures thatcontinue to age the seal face material. In applications where both faces are made of hardmaterials (for example, tungsten carbide and silicone carbide), distortions of the seal faces thatresult in excessive waviness can generate a much higher hydrodynamic pressure than undernormal conditions, thus causing a dramatic increase in fluid film thickness and leakage. In suchcases, the seal faces typically show no sign of wear or abnormal contact and the problem is only



4-16

recognized by inspecting the seal flatness. Local warpage of several light-bands over a smallcircumferential part of the seal was observed in a controlled test in which leakage was found toincrease by a factor of more than 100 during operation [52]. A more thorough heat treatment andstress relief prior to the final grinding and lapping operation can minimize distortions due tocontinued aging in operation.

4.4.8 Seal Faces Too Perfectly Flat to Generate a Film

As mentioned earlier, mechanical seals function well due to a small, unavoidable circumferentialwaviness (introduced by manufacturing tolerances or mechanical/thermal loads) that generateshydrodynamic lubricant film pressure at the sealing interface, which prevents direct asperitycontact between the faces. Under certain circumstances (fortunately rare), in which the seal facesare lapped too perfectly flat and the seal construction is robust enough to prevent mechanicaldistortion of the seal faces, the hydrodynamic film pressures are insufficient to separate the faces.This results in direct rubbing and very high friction, causing the seal temperatures to increaserapidly and immediate destruction of the seal. Evidence of high temperatures is also seen indiscoloration of the seal hardware. This type of failure was encountered in controlled laboratorytests performed under identical conditions for which a number of tests had been successfullyconducted previously [52]. It should be noted that, even though a maximum out-of-flatnesscriterion has been established by seal manufacturers, there is no minimum flatness requirementto ensure proper operation.

Key Technical Point

Conventional mechanical face seals rely on a small amount of waviness,automatically created by face distortions due to mechanical loads, tofunction properly. Too perfectly flat seal faces on structurally robust sealrings prevent the faces from distorting and developing a fluid film. Thisresults in seal failure due to seizure. Fortunately, this is a rare occurrence.

In conclusion, this section has described in detail all of the significant failure mechanisms thatcan cause seal failure, either singly or in combination. The insights provided here should be veryhelpful in following the systematic approach to troubleshooting and diagnosing seal failures inservice as outlined in Section 7.


5-1

5 APPLICATION AND SELECTION RECOMMENDATIONS

5.1 Introduction

The mechanical face seal represents a complex design that consists of several single-designcomponents. In order to achieve optimum performance, each of the single design componentsmust be selected to cover the operational requirements. Factors that affect the performance of theseal (and that should be considered when selecting a seal) include:

x Liquid type

x Liquid temperature during normal and design conditions

x Liquid pressure during normal and design conditions

x Rotational speed

x Radiation exposure

In addition to the above factors, the ease of maintenance is an important consideration inselecting a seal.

5.2 Selection Specification

In most power plants, the system liquid is either water or some type of hydrocarbon. The watermight be clean or contain abrasives that can significantly affect seal life if proper flushing is notprovided to remove the abrasives from the seal faces. In general, the following recommendationsare made depending on the process liquid.


Application and Selection Recommendations

5-2

Table 5-1Seal Application and Selection Guidelines

Application Typical Construction Installation Considerations

Water andfuel

The rubber bellows seal is commonly used forwater and fuel applications. The seal isrelatively inexpensive and typically uses arotating carbon head and a stationary metalface. To improve life and minimize abrasion, aceramic face is often used. Tungsten orsilicone faces are used in extreme cases.Bellows made from ethylene propylene areused up to 284qF (140qC) with water andwater-glycol mixtures. Fluoroelastomers areused for fuels up to a temperature of 302qF(150qC). Faces are typically loaded using asingle coil spring

Might require the use of doubleseals with a clean barrier liquid toprevent vaporization at the sealfaces and to provide betterlubrication for the seal faces.Borated water, which cancrystallize on the seal surfaces,must be externally flushed.Flushing of the interface by directjetting is mandatory for all liquidswith a specific gravity of less than0.63.

Boiler feed Demineralized water is a poor lubricant andthe face materials must be selected towithstand sparse lubrication. The seals areoften sleeve-mounted because the shaftspeed might approach 6,000 rpm. Faces areloaded using wave springs, welded springs, ormultiple springs.

If the pressure is high, doubleseals with a clean barrier liquidmight be required to stage thepressure drop. The barrier liquidmight also be circulated andcooled to remove heat away fromthe seal.

Mildcorrosives

Seals used in mild corrosives usuallyincorporate PTFE wedge secondary seals toprovide the required compatibility with theprocess liquid. Conventional O-ring andelastomeric bellows seals are also sometimesused provided they do not degrade in service.It is not uncommon to specify asymmetricformed metal bellows for higher temperatureapplications. Face loading is achieved usingmultiple springs or metal bellows.

Stainless steel components mightbe required to prevent corrosion.

Highly

corrosiveliquid

PTFE bellows are typically used in highlycorrosive liquids to prevent from escaping intothe environment. Asymmetric-formed metalbellows are also available for someapplications. The seals are usually externallymounted and have visual wear indicators thatsignal when the seal must be changed. Dualseals are also often used with a benign barrierliquid to minimize the toxic liquid escaping tothe environment. The seal faces are loadedusing multiple stainless steel springs or usingthe metal bellows seals.

Depending on the effects,corrosion might be eitherbeneficial or detrimental. If softoxides are formed, wear might bereduced as long as the oxidelayer is not disturbed. However,free hard oxide particles, floatingbetween the faces, can act asgrinders and increase wear. Inthose instances, flushing with aclean liquid might be required toenhance seal performance andlife.



5-3

Table 5-1 (cont.)Seal Application and Selection Guidelines

Application Typical Construction Installation Considerations

Hothydrocarbons

A wedge seal with multiple springs is used toseal hot hydrocarbons. The wedge is typicallymade of a high-temperature graphite if highpressure is encountered. Welded metalbellows are used for temperatures up to572qF (300qC) and pressures up to 290 psi(20 bars). Multiple springs are usually used toload the seal faces unless clogging can occur.When clogging is a problem, then a single coilspring is used.

Clean flushing liquid withlubricating properties are typicallyrequired to prevent volatile liquidsfrom vaporization in the vicinity ofthe seal interface. Vaporizationwill cause liquid film breakdownand loss of lubrication. Flushing ofthe interface by direct jetting ismandatory for all liquids with aspecific gravity of less than 0.63.

Slurry/dirtyprocess

Seals in slurry applications normally usedasymmetrically formed bellows to provide theseal on the primary ring and to load the faces.Bellows are typically made from corrosion-resistant materials and have no sharp cornersto trap contaminants. The static seals on thestationary ring are usually elastomeric O-rings. Hard faced materials are used for thefaces to prevent wear caused by theabrasives contained within the slurry.

Clean flushing liquid is typicallyrequired to remove abrasivesfrom the seal surfaces. Theflushing liquid should be neutralto prevent contamination of theprocess liquid. Cooling providedby flushing also improves seallife.

Key Technical Point

Seal selection requires a detailed and systematic evaluation of all thesignificant application parameters, for example, fluid type, pressure,temperature, speed, normal operating conditions versus design conditions,radiation exposure, and maintenance. Appropriate data sheets and checklists should be used to ensure a thorough and complete evaluation of suitablealternatives and trade-offs. Prototype qualification tests should beperformed for all critical applications.

5.3 Selection Data Sheet

The proper selection of a mechanical face seal requires examination of different areas of the sealinstallation and operating requirements. The following selection sheet provides guidance onrecognizing the critical area that must be identified. This data sheet was developed from the datasheets in API Standard 682. The more detailed data sheet in API 682 can be used in lieu of thisabbreviated data sheet. It is expected that the seal manufacturer might need to be contacted toassist in filling out the data sheet.



5-4

SELECTION DATA SHEET

1. Purchaser RequirementsPurchaser Company Date Pump service Plant item no. Ref pump drwg Enquiry Ref For proposal/purchase Seal mfg Seal installation drwg required, Y/N?

2. Application DetailsLiquid Seal Size Shaft/sleeve size Temperature range Sealed pressure range Speed range, rpm Rotation CW/CCW

3. Supplement Process DataPump suction pressure Pump discharge pressure Static pressure, max/min Vapor pressure at process temp Boiling temp at sealed pressure Vacuum pressure Abrasives Y/N Abrasives constituents Abrasives concentration Dissolved solids constituents Specific gravity of process Viscosity, max/min Auto-ignition temp Max/min ambient temp Corrosive/pH Carbon dioxide, ppm Dry running, Y/N Special operation comments

4. Process HazardHazard (state) Toxicity rating Allowable leakage

5. StandardsIdentify applicable compliance standards API ANSI NACE ISO DIN Other

6. Type of Installation (circle application selections)Single Double back-to-back Double face-to-face TandemCartridge Stationary mounted Clean flush can be usedCompatible sealant for double seal installation

7. Design Type (circle applicable selection)Rubber bellows O-ring PTFE wedge PTFE O-ringMetal bellows Unbalanced Balanced Single springMultiple springs Seal materials



5-5

SELECTION DATA SHEET (cont.)

8. Containment Seal in Addition to Item 6 (circle applicable selection)Non spark bushing Lip seal Labyrinth bushing MechanicalFloating labyrinth Standstill Other Maximum temperature Maximum Pressure

9. Auxiliary Fluids Available on SiteWater, Y/N Pressure Temperature Steam, Y/N Pressure Temperature Flush, Y/N Pressure Temperature Other, Y/N Pressure Temperature

10. Auxiliary Equipment to be Provided by Seal SupplierSealant system per attachment Cooler, type Cyclone separator Filter, type Flow controller Leakage detector type

11. Sealed Equipment DetailsPump Make/Model Pump, type Description Horizontal/vertical Axial/Radial split Seal mounted on shaft or sleeve Seals per pump Shaft axial movement Driver (electric motor, steam turbine, engine, etc) Wetted parts materials

12. Material Certification and Performance TestSpecify Certification Seal Test (std/spl)



5-6

5.4 Qualification Testing

In some critical service applications, where seal failure is unacceptable from a safety standpoint,or where the economic impact of failure is unacceptable (for example, unscheduled plantshutdowns), seal selection should be verified by appropriate qualification testing. This isespecially recommended where the manufacturers cannot provide reference experience for theselected designs from other similar applications.

The extent of testing, the key factors to be simulated, and parameters monitored during testingdepends upon the criticality of the application and the cost of performing the qualification tests.Guidance is provided in API Standard 682 [8] and in other publications related to mechanicalseals [7,56,57], which can be consulted to tailor the qualification testing for a specificapplication.


6-1

6 CONDITION-BASED MONITORING GUIDELINES

6.1 Introduction

Seal monitoring programs vary greatly from utility to utility, and from site to site. Some of this isthe result of different equipment designs, operating philosophies, and different rates of forcedoutages experienced. Based on survey results, the level of condition monitoring required todevelop reliable seal performance data is quite basic except for main coolant pump mechanicalface seals. For many plants, condition based monitoring is limited to visual observations withlittle actual quantification.

This section of the guide provides information on how to evaluate seal performance andsuggestions for monitoring and data acquisition. The data acquired and tended can be used toassess seal performance and to provide reasonable predictions of the remaining life or operabilityof a mechanical face seal. The parameters to be trended will be identified, evaluation described,and examples provided. Trouble-shooting problems require good data. Without a trendingprogram, determining the root cause of an operating problem is difficult, if not impossible.

Data logging of the various parameters associated with mechanical face seals can be performedin many different ways. The simplest way is to use manual recording, however, sophisticateddata-logging systems can also be utilized. Hand logging of data and trending is time consuming,but it is effective in trending most seal performance characteristics over the long term. Requiredparameters that are routinely trended can be added to the daily or shift logs recorded by theoperators. These parameters can then be plotted using standard spreadsheet programs and trendscan be maintained and provided to plant personnel as part of the normal system status reports.

The major advantages of automated systems are that data can be routinely recorded anddownloaded to trending programs, and changes in the frequency of data-logging can be triggeredfrom performance changes. Generally, when analyzing seal performance changes, it is necessaryto have data recorded frequently or to have key parameters on continuous recorders. Theseautomated systems are reasonably expensive and, in a time where utilities are being challengedto hold the line on costs, are only appropriate for systems with a relatively high frequency of sealfailures.

Key O&M Cost Point

Seal monitoring programs vary greatly from utility to utility and from site tosite due to different equipment designs, operating philosophies, and differentrates of forced outages experienced. For many plants, condition-basedmonitoring is limited to visual observations with little actual quantification,except for main coolant pump mechanical face seals.


Condition-Based Monitoring Guidelines

6-2

6.2 Typical Performance Data Logging

Data that is typically available for logging includes pressures, temperatures, flows, vibrationlevels, and, in some cases, speed. The amount of each type of data collected for each seal willdepend on the type of seal used and its installation. For example, single seals will require lessdata collection than double or tandem seal arrangements. The frequency of data logging will varyfrom system to system based on system conditions and seal operating experience andcharacteristics. Manual recording might be required only once a day. Automated data-loggingsystems can acquire data at any frequency, and the frequency can be dynamically adjusteddepending on seal performance. A typical log sheet for a multiple seal arrangement and itssupport system is shown in Table 6-1.

An example of pressure being used to trend seal performance is illustrated in Figure 6-1 for astaged seal arrangement. In this example, the lower seal stage differential pressure is plottedagainst time and a best guess projection is made to predict when the failure limit has beenreached. Similar trends can be plotted of temperature in a barrier fluid or loss of barrier fluid inthe barrier fluid reservoir. Loss of barrier fluid can be very useful in characterizing sealperformance in a corrosive system seal arrangement.



6-3

Table 6-1Seal System Log Sheet

Plant Unit

System Equip. No.

Date Time Recorded By:

Seal No. 1

Item Normal Minimum Maximum Startup

Flow

Temperature

Differential Pressure

Backpressure

Frame Vibration level

Shaft Vibration level

Speed

Leakage rate

Seal No. 2

Flow

Temperature


Backpressure

Seal No. 3

Flow

Temperature


Backpressure

Flush

API Plan No. Fluid type

Flow rate

Temperature, inlet

Pressure

Filtration

Quench/Drain

API Plan No. Fluid type

Flow rate

Temperature, inlet

Temperature, outlet

Pressure

Filtration



6-4

Figure 6-1Seal Data Plot Showing Declining Performance (Courtesy of Southern California Edison)



6-5

6.3 Seal Performance Parameters

Other than seal dynamic torque, seal face temperatures and seal face temperature changes are thekey measures of the performance of a seal because they characterize what is happening at theseal interface. Seal dynamic torque is almost impossible to measure and is, therefore, not a viablemeasurement. Temperature is the easiest parameter to measure and, depending on the sealarrangement, temperature measurements can directly characterize seal performance. Usuallytemperature data in the vicinity of the seal are a measure of the process fluid or support system,especially in seal systems that are flushed or quenched. These temperature measurements tend tomask the actual seal performance and many times fail to provide meaningful data. The moreobvious measure of seal performance is leakage, but this method is only viable for single seals oroutboard seals of multiple seal arrangements. In systems where only a small leak is acceptable,leakage measurement fails to provide an indication of impending failure.

Even within these limitations and short falls, data taken to monitor seal performance can providea useful tool. These measurements become even more meaningful when tracked over anextended period of time and correlated to seal failure. Parameters such as pressure and flow,which do not directly characterize seal performance but do affect seal performance, becomeextremely important when predicting when the seal might fail.

Key O&M Cost Point

Monitoring and data logging of key performance parameters can serve asvery useful tools for trending wear and performance degradation ofmechanical seals and preventing unscheduled outages.

6.4 Instrumentation

Seal monitoring can be accomplished with simple and easy-to-implement manual instrumentssuch as temperature and pressure gauges, or with complex computer data-acquisition systemsthat can initiate controls based on parameter limits. This section describes the manual sensorsand switches that are commonly available and used. When used, the sensors should comply witha recognized standard such as API Standard 682. Electronic sensors, such as pressuretransducers, thermocouples, etc., should be subject to similar design requirements. The followingsections (6.4.1 through 6.4.8) that outline various sensors and switches are based onrecommendations contained in the API Standard 682. Deviations from the followingrecommendations can be made, and other design requirements might be imposed, based onspecific needs of the plant.

6.4.1 Temperature Gauge

Temperature gauges provide a visual indication of the local temperature. The sensing element isin contact with the liquid being measured.



6-6

Dial temperature gauges should be heavy-duty and corrosion resistant. They should be bi-metallic or liquid-filled, with a rigid stem suitable for mounting as needed. Mercury-filledthermometers are not acceptable. Black printing on a white background is standard.

Dial temperature gauges should be installed in pipe sections or in tubing runs. The sensingelement of temperature gauges should be in the flowing fluid to the depth specified by the gaugemanufacturer.

Temperature gauges installed in tubing should be a minimum of 1 1/2 inches (38 mm) indiameter and the stem should be a minimum of 2 inches (50 mm) long. All other gauges shouldbe a minimum of 3 1/2 inches (90 mm) in diameter and the stem should be a minimum of 3inches (75 mm) long.

6.4.2 Thermowells

Thermowells provide protection for the sensing element of temperature gauges.

Temperature gauges that are in contact with flammable or toxic fluids, or that are located inpressurized or flooded lines, should be furnished with separable threaded solid-bar thermowellsmade of AISI Standard Type 300 stainless steel or another material more compatible with theliquid as defined by the manufacturer. Thermowells installed in piping should be 1/2 inch-NPTminimum. Thermowell designs and installation should not restrict liquid flow.

6.4.3 Pressure Gauges

Pressure gauges provide a visual indication of the pressure and the sensing element is in contactwith the liquid being measured.

Pressure gauges should conform to ANSI/ASME Standard B.40.1 grade 2A. The gauges shouldbe furnished with AISI Standard Type 316 stainless steel bourdon tubes or other materialcompatible with the liquid, stainless steel movements, and 1/2-inch NPT male alloy steelconnections with wrench flats. Gauges installed in tubing should have 2 1/2-inch (64 mm)diameter dials. Gauges not installed in tubing should have 4 1/2-inch (114 mm) diameter dials.Black printing on a white background is standard for gauges. Gauge range should be selected sothat the normal operating pressure is at the middle of the gauge's range. In no case, however,should the maximum reading on the dial be less than the applicable relief valve setting plus 10percent.

6.4.4 Alarm, Trip, and Control Switches

Alarm, trip, and control switches provide a visual or audible signal or control an electric circuitwhen the preset limit of a sensor has been exceeded.

Each alarm switch, each shutdown switch, and each control switch should be furnished in aseparate housing located to facilitate inspection and maintenance. Hermetically-sealed, double



6-7

pole, double throw switches, with a minimum rating of 5 amperes at 120 volts AC and 1/2ampere at 120 volts DC, should be used. Mercury switches should not be used.

Unless otherwise specified, electrical switches that open (de-energize) to alarm and close(energize) to trip should be furnished.

Alarm and trip switch settings should not be adjustable from outside the housing. Alarm and tripswitches should be arranged to permit testing of the control circuit, including when possible, theactuating element, without interfering with normal operation of the equipment. If a shutdownsystem is being implemented, the need for bypass indication and testing features should beconsidered.

Pressure-sensing elements should be of AISI Standard Type 300 stainless steel. Low-pressurealarms, which are activated by falling pressure, should be equipped with a valved bleed or ventconnection to allow controlled depressurization so that the operator can note the alarm setpressure on the associated pressure gauge. High-pressure alarms, which are activated by risingpressure, should be equipped with a valved test connection so that a portable test pump can beused to raise the pressure.

All switches sensing the same variable should have reset ranges, such that changing the variableto reset one switch does not activate other switches.

6.4.5 Pressure Switches

Pressure switches trip when a pre-set pressure limit has been exceeded. Pressure switches canhave low and/or high limit settings.

Pressure switches should have over-range protection to the maximum pressure to which theswitch can be exposed. Switches exposed to vacuum should have under-range protection to fullvacuum.

The measuring element and all pressure-containing parts should be AISI Standard Type 316stainless steel unless the pumped fluid requires the use of alternate materials, as determined bythe seal manufacturer. Unless otherwise specified, pressure switches should be bellows ordiaphragm. Connections for pressure input should be 1/2-inch NPT. Connection for the airtransmission signal should be 1/4-inch NPT.

6.4.6 Level Switches

Level switches trip when a pre-set liquid level has been exceeded. Level switches can have lowand/or high limit settings.

Unless otherwise specified, level switches should be hydrostatic, capacitance, or ultrasonic.



6-8

Be aware that level switches might have a dead band wide enough to activate other switchesduring re-setting. This is especially true when dealing with the small volumes of barrier fluidsassociated with dual-seal reservoirs.

6.4.7 Level Indicators

Level indicators provide a visual indication of the liquid level and are also used when dealingwith small volumes of barrier fluids associated with dual-seal reservoirs. The standard levelindicator should be the weld pad reflex design.

When specified, an externally mounted, removable, reflex indicator should be furnished insteadof the standard weld pad design.

6.4.8 Flow Indicators

A flow indicator provides a visual indication of flow rate and, when used, should be a steel bodynon-restrictive bull's eye.

To facilitate viewing of flow through the line, each flow indicator should be installed with itsbull's-eye glass in a vertical plane. The diameter of the bull's eye should be at least one-half ofthe inside diameter of the line in which it is installed and should clearly show the minimum flow.


7-1

7 TROUBLESHOOTING TO IDENTIFY CAUSE OF SEALFAILURE

Key O&M Cost Point

Seal performance is often directly linked to equipment performance andreliability. An in-depth inspection and review of seal failures can improveequipment availability and performance.

7.1 Introduction

A discussion of the fundamental mechanisms responsible for seal failure was presented inSection 4. To improve seal reliability and extend its life in a particular application, a thoroughanalysis of the cause of failure of a mechanical seal often gives the best indication of actionrequired. This section provides a comprehensive step-by-step troubleshooting approach that canbe followed by engineers and operating and maintenance personnel to diagnose seal failures inactual applications.

Several excellent sources, including seal manufacturers' published information and sealhandbooks, identify causes of seal failure and provide illustrations of failed parts to aid indiagnosis [3,7,11-19]. The troubleshooting approach and tables in this section are based onrelevant information for nuclear and fossil power applications from these sources along with theauthor’s experience in root cause analysis of seal failures. A number of the illustrations andtechnical notes included in the tables in this section were obtained from John Crane MechanicalSeals and Mechanical Engineering Publications, Ltd., London [7,17]. They have been updatedand are used here with permission from these organizations.

7.2 Failure Diagnosis

Seal failure diagnosis is very similar to any other failure investigation and often the bestindication of the cause of failure is from visual examination of the seal itself. Once the likelycause of the problem is decided, the available solutions are usually clear. It is very important tokeep in mind that evidence of seal failure is an essential element in determining the cause of sealfailure and if the evidence is lost there is no way to back track. Therefore, to reduce the risk oflosing evidence, it is suggested that a systematic step-by-step approach be followed during theinvestigation process.


Troubleshooting to Identify Cause of Seal Failure

7-2

x Properly document external symptoms of seal failure

x Perform detailed checks before dismantling

x Clearly document evidence during dismantling and disassembly

x Perform detailed visual examinations of seal components

7.2.1 External Symptoms of Seal Failure

A useful indication of the cause of a seal problem can often be obtained by analysis of thesymptoms experienced in service. These might suggest either the remedy directly or at least thedirection of subsequent failure diagnosis. On critical duties, instrumentation might be availableto give further assistance, or portable devices can be used for condition checks.

Table 7-1 outlines various external symptoms of seal failure and their possible causes, and offersrecommendations for managing the symptoms.



7-3

Table 7-1External Symptoms of Seal Failure

Symptom Possible Causes Recommendations/Remarks

Seal squeals duringoperation

Inadequate amount of liquidto lubricate seal faces (Notethat not all dry seals squeal.)

x If not in use, a bypass flush line might berequired. If already in use, the line orassociated restrictions, for example,orifices in the gland plate, might need to beenlarged.

x If increase in leakage is permissible, useseal designs with positive hydrodynamiclubrication features, for example, facenotches, laser-textured seal faces

Carbon dustaccumulating onoutside of seal area

Inadequate amount of liquidto lubricate seal faces

See above

Liquid film vaporizing/flashing between seal faces.In some cases, this leaves aresidue that grinds away thecarbon-graphite seal ring.

Pressure in seal chamber might beexcessively high for the type of seal and thefluid being sealed. See below for actionsagainst vaporization.

Seal spits and sputtersin operation (oftencalled popping)

Product vaporizing/flashingacross the seal faces

Remedial action is aimed at providing apositive liquid condition of the product at alltimes

x Increase seal chamber pressure if it ispossible to remain in seal operatingenvelope

x Check for proper balance design with sealmanufacturer

x Change to a seal design not requiring somuch product temperature margin

x If not in use, a bypass flush line will berequired

x If already in use, the bypass flush line orassociated restrictions might need to beenlarged

x Increase cooling of seal faces

x Check for seal interface cooling with sealmanufacturer

x If increase in leakage is permissible, useseal designs with positive hydrodynamiclubrication features, for example, facenotches, laser-textured seal faces.

Note that a review of balance design requiresaccurate measurement of seal chamberpressure, temperature, and specific gravity ofproduct.



7-4

Table 7-1 (cont.)External Symptoms of Seal Failure


Seal drips or leakssteadily

If possible, first determine the source of the leakage. Heavy leakage isnormally from the faces rather than the O-ring, and so on.

Insufficient load on the sealfaces

Primary seal concerns:

x Faces not flat

x Faces cracked, chipped,or blistered

x Distortion of seal facesfor thermal or mechanicalreasons (usuallydetermined from wearpattern on faces)

Typical corrective actions:

x Check for incorrect installation dimensionsor loosening of set screws duringoperation, permitting axial slippage.

x Check for improper seals or material beingused in the application.

x Check gland gasket for propercompression.

x Check for gland plate distortion because ofover-torquing of gland bolts (this can causefaces to become distorted).

x Clean out any foreign particles betweenseal faces. Relap faces or renew.

x Check for any installation or similardamage and renew if necessary.

x Check for squareness of stuffing box toshaft and similar equipment conditionconcerns.

x Ensure pipe strain or machinemisalignment is not causing distortion ofseal faces (especially end suctionoverhung type pumps).

x Improve cooling flushing lines.

Secondary seal concerns:

x Secondary seals nicked orscratched duringinstallation

x Leakage of liquid underpump shaft sleeve

x Overaged O-ring

x Compression set ofsecondary seals (hard andbrittle)

x Chemical attack ofsecondary seals (soft andsticky)

Typical corrective actions

x Renew secondary seals.

x Check for proper lead in chamfers, burrremoval, and so on.

x Check for correct seals with manufacturer.

x Check for correct seal materials withmanufacturer.



7-5



Seal drips or leakssteadily (cont.)

Seal hardware concerns:

x Spring failure

x Erosion damage ofhardware

x Corrosion of drivemechanisms

Typical corrective actions:

x Renew parts

x Check for improved material availability

x Modify recirculation flow arrangement toreduce high velocity jets on hardware.Install cyclone separator to remove solidsfrom recirculation flow

Pump/shaft vibration x Misalignment

x Impeller/shaft systemimbalance

x Cavitation

x Bearing problems

This will reduce seal life even though leakagemight not be immediately apparent.

Short seal life Equipment mechanically outof line (for example, fromundue pipe strain)

See above. In the extreme, this can causerubbing of the seat on the shaft

Abrasive product (causingexcessive seal face wear)

Typical actions are aimed at determining thesource of abrasives and preventing themfrom accumulating at the seal faces

x If abrasives are in suspension, bypassflushing over the seal faces will improvethe situation by keeping the abrasiveparticles moving and so reducing theirtendency to settle out or accumulate inthe seal area. A cyclone separator is oftenadded to this bypass line (filters givelonger term problems unless regularlycleared).

x When abrasives are forming locally in theseal area, a bypass flush will helpintroduce the maximum product to theseal cavity at the correct temperature.Abrasives form in the area because of theprocess liquid cooling down andcrystallizing or partly solidifying, orbecause of local product evaporation.



7-6



Short seal life (cont.) Seal running too hot x Check that all cooling lines are connectedand operational

x Check that flow is not obstructed incooling lines or jackets (for example, fromscale formation)

x Increase the capacity of cooling lines

x A recirculation or bypass flush line mightbe necessary

x Check for possible rubbing of a sealcomponent against the shaft (see alsoOKUCNKIPOGPV above). Some good pointsto check are: neck bush clearance,clearance between the rotating seal unitand the seal chamber bore, the bore ofthe seat, and the seal plate clearancefrom the sleeve.

Inadequate seal type or sealmaterial for duty.

If there is a concern, advice is readilyavailable from seal manufacturers. Sealmaterial deficiencies might well result indeterioration from corrosion or excessiveheat.

Seal leaks excessivelyfollowing a pressureand temperaturetransient

Seal wears into a pattern andtransients can causeexcessive positive or negativeconing of the seal faces.Coning changes the filmpressure distribution, whichcan either cause face partingof balanced seals with lowbalance ratio or cut off theentrance of the lubricant/fluidbetween the seal faces. Lossof film causes heat damage.

x Use seal with higher balance ratio if faceparting is encountered

x Control seal environmental temperatureby a suitable flushing arrangement

x Use seal designs with enhanced fluid filmlubrication features at the seal faces, forexample, cooling notches, hydropads



7-7

7.2.2 Checks Before Dismantling

In addition to noting any seal failure symptoms, other checks prior to disassembly can bevaluable, either directly or to facilitate later diagnosis. Most of these checks are straightforwardand are carried out as routine by most engineers. Thus, they are presented as a checklist in Table7-2 to act as an aide.


The importance of maintaining As Found conditions is important to failuremode determinations. Personnel should be instructed to exercise careduring the disassembly steps.

Table 7-2Checklist of Actions Before Dismantling

Topic Checklist

Documentation Take photographs of all key components and subassemblies beforeand during disassembly

Toxic/hazardous product In such cases, all necessary precautions are to be observed prior andduring assembly. Consult material safety data sheets (MSDS).

Service life of seal Hours of operation. Duty cycle, stop/starts, and so on.

Process change Identify any change - often the key to a solution

Seal might have been selected on theory of process, not practice

Changes in fluid pressure, temperature, or composition

Process variation or fluctuation

Background informationrequired

Fluid sealed (including contaminants)

Fluid pressure on seal and in system

Fluid temperature at seal and in system

Fluid flow within the seal chamber

Sealed fluid vapor pressure/temperature data

Operating shaft speed(s)

Special operating conditions

Machine assembly drawing

Seal assembly drawing

Seal design data

Machine vibration Useful even when not immediately apparent as a symptom

Axial and radial bearing housing or shaft vibration

Frequency analysis to confirm out-of-balance, misalignment, etc., untilmachine can be stopped for physical checks



7-8

Table 7-2 (cont.)Checklist of Actions Before Dismantling

Topic Checklist

Seal leakage pattern Safety note: all necessary precautions must be observed during anyleakage checks, especially if the fluid is toxic or hazardous.

Amount and nature of abnormal leakage?

Leakage constant or variable?

Leaks when shaft is stationary?

Leaks when shaft is rotating?

Related to changes of speed, pressure, or temperature of operation?

Possible leakage path(s) An assembly drawing is of great assistance.

If possible, identify source of abnormal leakage while machine is stilloperating.

Inspect exposed machine surfaces for indications of leakage path(s),for example, along shaft, under sleeve, from seal plate gaskets, andso on.

This inspection to continue through subsequent equipment and sealdismantling until the leakage path(s) are all found.

Typical leakage paths:

x Face leakage

x Secondary seal on primary ring

x Secondary seal on mating ring

x Seal/gasket on seal plate(s)

x Seal/gasket under shaft sleeve

x Cracked or damaged housing component

Hydrostatic testing If possible, for example with double seals, bench testing of equipmentcan be a useful method of identifying the leak path.

With other seal layouts, a suitable test fixture for subassemblypressure testing might be justifiable if large numbers of seals are beingexamined.



7-9

7.2.3 Checks During Dismantling

For proper diagnosis of seal problems, several checks and observations should be made duringthe dismantling of a mechanical face seal. These observations are divided into three categories:general, premature failure, and mid-life failure checks, and are given in the checklist Tables 7-3,7-4, and 7-5.

7.2.3.1 General Checks

Table 7-3General Checks During Dismantling

Topic Checklist

Seal surfaces Avoid disturbing the seal surfaces

Avoid wiping or cleaning the faces more than is necessary for safedisassembly

Visual examination of seal faces is included in Section 7.3

Dimensional checks The necessary marks and measurements to determine are:

x Seal working length

x Squareness of seal faces to shaft axis

x Concentricity of seal faces to shaft axis

x Shaft end play

x Shaft radial run out, whip and deflection

Possible leakage path(s) Examination of surfaces as they become exposed for all possiblecauses of abnormal leakage

Deposits and debris Examination prior to cleaning for:

x Foreign contaminants

x Wear debris

x Small fragments or chips from broken components

x Corrosion products

x Miscellaneous debris/deposits

Seal hang-up Check for hang-up by flexing the seal slightly above and below itsinstalled working length

Seal sub-assembly cleaning Avoid removing or obscuring any vital evidence on the seal failuremechanism (especially on the seal faces)

Avoid using wire brushes, sharp tools, abrasive cleaners, or powerfulsolvent cleaning agents (which can attack the elastomericcomponents)

Packaging For seal manufacturer examinations/repair:

x Many seal makers will personally collect unusual/critical seals forfailure diagnosis

x Packaging needs to be of high standard (as for new seals)

x Avoid wire mounted identification tags, etc., that can damage partsin transit



7-10

7.2.3.2 Premature Failure Checks

Table 7-4Premature Failure Checks During Dismantling

Topic Checklist

Seal faces Examination for nicks, scratches, and fractures:

x Low power magnification can assist

Examination of non-uniform contact pattern:

x Dirt trapped between the faces

x Distortion of one or both faces

x Improperly finished faces

x See also Appendix B optical flat checking

Examination for thermal distortion:

x From running dry

x Heat checks/thermal cracking

x Pitting, grooving, galling, spalling, blistering, and so on

Secondary seals Examination for :

x Omitted seals

x Misassembled seals

x Nicks, extruded, or distorted static seals

x Score marks from relative rotational movement betweensecondary seals and mating surface

x Excessive volume change or compression set

x Fretting of sealing surfaces at secondary seal positions

Drive mechanism Examination for:

x Mis-assembly

x Mis-indexing

x Omission

Check for loss of secondary seal interference when used for drivepurposes, for example, static seals and bellows

Face loading hardware Examination for:

x Incorrect type

x Mis-assembly

x Mis-indexing

x Omission



7-11

7.2.3.3 Mid-Life Failure Checks

Table 7-5Mid-Life Failure Checks During Dismantling

Topic Checklist

Seal faces Examination for nicks, scratches, and fractures:

x Overall corrosion

x Leaching

x Abnormal grooving

x Erosion damage

x Excessive pitting, galling, and spalling

x Thermal damage such as waviness, heat checks, cracks, blisters, deposition ofsolid material, and overall thermal discoloration

Wear profile check by:

x Naked eye examination

x Use of low incidence angle light to highlight features

x 10X magnification, then 50X

x Measurement to determine the amount of wear

Secondaryseals

Examination for:

x Extrusion

x Chemical attack on both seal and its interface surfaces

x Excessive volume damage

x Excessive compression set

x Hardening and cracking

Drivemechanism

Examination for:

x Failure

x Excessive wear

x Check for loss of secondary seal interference when used for drive purposes, forexample, static seals and bellows



7-12

7.3 Visual Seal Examination

The symptoms experienced might not be the prime cause of failure. It is often necessary toidentify the root cause in order to avoid a recurrence. Once the likely cause of the problem isdecided, the available solutions are usually clear. There are cases, however, where further checksare necessary to clarify diagnosis. There are also proven remedies for particular concerns.Therefore, this section notes likely causes, further checks, and proven remedies, as appropriate,for each symptom.


Visual examination is an important element in determining failuremechanisms. Personnel should be attentive during disassembly to be alertfor evidence of incipient or chronic failure mechanisms.

As there are a relatively large number of ways a mechanical seal can fail (this section lists 45), itis helpful to group them alpha-numerically, as shown in Table 7-6 below. This split is somewhatarbitrary and several failure modes are caused by a complex mixture of mechanical, thermal,and/or chemical aspects. However, it does show a pattern, which can be helpful when using thesubsequent extensive table of common seal, failure modes. Table 7-7 is similarly divided intothree parts: seal faced, secondary seals, and seal hardware.



7-13

Table 7-6Visual Examination: Failure Symptoms Based on Mechanical, Thermal, or ChemicalDamage

Contact Pattern Mechanical Thermal Chemical

Seal faces A1: Proper contactpattern

A2: No contactpattern

A3: Heavy outsidediametercontact

A4: Heavy insidediametercontact

A5: Wide contactpattern

A6: Eccentriccontact pattern

A7: Contact withone high spot

A8: Contact at twoor more highspots

A9: Contactthrough 270q

A10: Contact atgland boltlocations

A11: Fracture

A12: Scratches andchips

A13: Adhesive wear

A14: Abrasive wearA15: Grooving and

severe wearA16: Erosion of

carbon ring

A17: Thermaldistress, over360q

A18: Thermaldistress over120q - 180q

A19: Thermaldistress inpatches

A20: Coking

A21: Carbonchemical attack

A22: Corrosion ofmetal faces

A23: Corrosion ofhard faces

A24: Flaking andpeeling

A25: Crystallization

A26: SludgingA27: Bonding

A28: Blistering

Secondaryseal

B1: Physicaldamage

B2: ExtrusionB3: Excessive

torque

B4: Hard or crackedelastomer

B5: Compressionset of elastomer

B6: Elastomerchemical attack

B7: Corrosion atsecondary sealinterfaces

Sealhardware

C1: Physicaldamage

C2: Hardwarerubbing

C3: Erosion orabrasive wear

C4: Drive failure

C5: Spring distortionand breakage

C6: Seal hang-upC7: Sleeve marking

and damage

C8: Overheatedmetalcomponents

C9: Corrosion ofseal hardware

C10: Excessivedeposits

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7-14

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atte

rnT

ypic

al c

onta

ct p

atte

rn o

f a n

on-le

akin

g se

al.

Ful

l con

tact

thro

ugh

360

degr

ees

on th

e se

atsu

rfac

e w

ith li

ttle

or n

o m

easu

rabl

e w

ear

onei

ther

sea

l rin

g.

If le

akag

e is

pre

sent

, sus

pect

x

the

seco

ndar

y se

als

and,

in th

is s

ituat

ion,

the

seal

typi

cally

drip

s st

eadi

ly w

ith th

esh

aft s

tatio

nary

or

rota

ting.

x

war

page

of t

he s

eal f

aces

due

to th

erm

alag

ing

and

inco

mpl

ete

stre

ss r

elie

f of t

hese

al f

ace

mat

eria

l dur

ing

oper

atio

n.

Cau

ses

Leak

age

is m

ost c

omm

only

from

sec

onda

ryse

als

but i

n so

me

case

s du

e to

exc

essi

vew

avin

ess

of th

e se

al fa

ces

due

to h

igh

tem

pera

ture

exp

osur

e du

ring

oper

atio

n.

Ch

ecks

x

Sec

onda

ry s

eals

nic

ked

or s

crat

ched

or

inst

alla

tion.

If s

o, r

enew

sea

ls, h

avin

gch

ecke

d fo

r pr

oper

lead

in c

ham

fers

,re

mov

ed b

urrs

, and

so

on.

x

Che

ck s

econ

dary

sea

ls f

or d

amag

e, p

oros

ity,

ther

mal

or

chem

ical

atta

ck.

x

Che

ck fo

r co

mpr

essi

on s

et o

f o-

ring.

x

Che

ck fo

r co

rrec

t mat

eria

l with

sea

lm

anuf

actu

rers

.

x

Sea

l han

g up

(se

e C

6 be

low

).

x

Che

ck fa

ce fl

atne

ss.

x

Pip

ewor

k di

stor

tion.

Rem

edia

l Act

ion

x

Pro

vide

lead

-in c

ham

fers

.

x

Rem

ove

burr

s.

x

Lubr

icat

e se

cond

ary

seal

s.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-15

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A2:

No

cont

act p

atte

rnT

his

indi

cate

s th

at th

e ro

tary

face

is n

ot tu

rnin

gag

ains

t the

sta

tiona

ry fa

ce.

Cau

ses

Pos

sibi

litie

s in

clud

e th

e fo

llow

ing:

x

Impr

oper

inst

alla

tion.

x

Slip

ping

of t

he r

otar

y dr

ive

mec

hani

sm.

x

Inte

rfer

ence

of a

rot

ary

with

a s

tatio

nary

com

pone

nt, f

or e

xam

ple,

sea

l bod

y w

ith s

eal

cham

ber

bore

.

A3:

Hea

vy o

utsi

de d

iam

eter

con

tact

(neg

ativ

e co

ning

or

rota

tion)

Hea

vy c

onta

ct o

n th

e se

alin

g rin

g an

d th

e se

atat

the

outs

ide

diam

eter

of t

he s

ealin

g pl

ane.

Fad

es a

way

to n

o vi

sibl

e co

ntac

t at t

he in

side

diam

eter

of t

he c

onta

ct p

atte

rn.

Pos

sibl

e ed

gech

ippi

ng o

n th

e ou

tsid

e di

amet

er o

f the

sea

ling

ring.

Cau

se

Usu

ally

cau

sed

by th

e fa

ces

not b

eing

flat

beca

use

of o

ver-

pres

suriz

atio

n of

the

seal

.

Ch

ecks

Can

als

o oc

cur

from

:

x

Inco

rrec

t lap

ping

, lea

ving

the

seal

face

s no

tfla

t.

x

Exc

essi

ve s

wel

l of c

onfin

ed s

econ

dary

sea

ls.

x

Impr

oper

sea

l fac

e su

ppor

t sur

face

.

x

Ent

rapm

ent o

f for

eign

par

ticle

s.

x

The

rmal

eff

ects

(us

ually

on

ID; s

ee A

17-A

19be

low

).

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-16

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A4:

Hea

vy in

side

dia

met

er c

onta

ct(p

ositi

ve c

onin

g or

rot

atio

n)H

eavy

con

tact

on

the

seal

ing

ring

and

the

seat

at th

e in

side

dia

met

er o

f the

sea

ling

plan

e.F

ades

aw

ay to

no

visi

ble

cont

act a

t the

out

side

diam

eter

of t

he c

onta

ct p

atte

rn.

Pos

sibl

e ed

gech

ippi

ng o

n th

e in

side

dia

met

er o

f the

sea

ling

ring.

Sea

l lea

ks s

tead

ily w

hen

the

shaf

t is

rota

ting

and

usua

lly n

o le

akag

e w

hen

the

shaf

t is

stat

iona

ry.

Cau

se

Typ

ical

ly c

ause

d by

ther

mal

dis

tort

ion

of s

eal

face

s.

Ch

ecks

Als

o ca

n oc

cur

from

cau

ses

liste

d ab

ove

unde

rhe

avy

outs

ide

diam

eter

con

tact

, A3.

Rem

edia

l Act

ion

s

x

Impr

oved

coo

ling

of th

e se

al.

x

Cha

nges

of

seal

mat

eria

l.

A5:

Wid

e co

ntac

t pat

tern

Con

tact

pat

tern

is c

onsi

dera

bly

wid

er o

n th

ese

at th

an th

e fa

ce w

idth

of t

he s

ealin

g rin

g.P

ossi

ble

wea

r at

driv

e no

tche

s if

pres

ent i

nse

alin

g rin

g.

Sea

l doe

s no

t lea

k w

hen

shaf

t is

stat

iona

ry, b

utle

aks

stea

dily

whe

n sh

aft i

s ro

tatin

g.

Cau

se

Pos

sibi

litie

s in

clud

e th

e fo

llow

ing:

x

Pum

p m

isal

ignm

ent -

this

mig

ht a

lso

caus

ese

al to

han

g-up

on

the

shaf

t.

x

Pip

e st

rain

.

x

Bea

ring

failu

re o

r ex

cess

ive

clea

ranc

e.

x

Ben

t sha

ft.

x

Sha

ft w

hirl

of la

rge

ampl

itude

.

x

Pum

p ca

vita

tion.

x

Pum

p vi

brat

ion.

x

Mis

alig

ned

seat

.

x

Pum

p op

erat

ion

outs

ide

spec

ifica

tion.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-17

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A6:

Ecc

entr

ic c

onta

ct p

atte

rnE

ccen

tric

con

tact

pat

tern

on

the

seat

with

wid

thof

con

tact

equ

al to

sea

ling

ring

thro

ugh

360°

.S

eat m

ight

hav

e co

ntac

t mar

ks o

n its

inte

rnal

bore

or

loca

l cra

ckin

g (f

rom

a s

haft

rub)

. N

oab

norm

al w

ear

on s

ealin

g rin

g if

seat

isun

dam

aged

.

No

leak

age

if th

e sh

aft h

as n

ot c

onta

cted

the

insi

de d

iam

eter

of t

he s

eat.

If s

eat i

s da

mag

ed,

then

leak

age

will

occ

ur w

hen

the

shaf

t is

rota

ting

or s

tatio

nary

.

Cau

se

7UWCNN[

ECWUGFD[COKUCNKIPGFUGCV�

Ch

ecks

x

Che

ck fo

r co

rrec

t sea

t des

ign

and

clea

ranc

es.

x

Che

ck fo

r co

rrec

t cle

aran

ces

betw

een

the

glan

d pl

ate

and

the

seal

cha

mbe

r.

x

Che

ck fo

r co

ncen

tric

ity b

etw

een

the

outs

ide

diam

eter

of t

he s

haft

slee

ve a

nd th

e in

side

of

the

seal

cha

mbe

r.

A7:

Con

tact

with

one

hig

h sp

otC

onta

ct p

atte

rn o

n se

at th

roug

h 36

0° s

light

lyla

rger

than

the

seal

ing

ring

face

wid

th. H

igh

spot

or h

ighl

y po

lishe

d ar

ea m

ight

be

pres

ent o

n th

ese

at (

for

exam

ple,

opp

osite

a d

rive

pin

hole

or

atlo

catio

n of

ant

i-rot

atio

n pi

n if

not c

orre

ctly

asse

mbl

ed in

to h

ole)

. S

eat w

ithou

t sta

tic s

eal(s

)w

ill r

ock

or m

ove

in g

land

pla

te o

r ho

lder

. W

ear

at d

rive

notc

hes

if pr

esen

t in

seal

ing

ring.

Sea

l doe

s no

t lea

k w

hen

shaf

t is

stat

iona

ry, b

utle

aks

stea

dily

whe

n ro

tatin

g.

Cau

se

Mat

ing

surf

aces

are

not

squ

are.

Ch

ecks

x

Che

ck th

at th

e se

al p

late

sur

face

in c

onta

ctw

ith th

e se

at is

free

from

nic

ks/b

urrs

and

show

s a

full

patte

rn w

hen

blue

d w

ith s

eat.

x

Che

ck th

at a

nti-r

otat

ion

pin

is c

orre

ctly

loca

ted

into

sea

t.

x

Che

ck th

at a

nti-r

otat

ion

pin

does

not

bot

tom

into

the

seat

.

x

Che

ck fo

r co

rrec

t ext

ensi

on o

f al

l driv

e pi

nsfr

om s

eal p

late

.

x

Che

ck fo

r ad

equa

te s

haft

alig

nmen

t (to

avo

idit

pass

ing

thro

ugh

the

seal

cha

mbe

r at

an

angl

e).

x

Che

ck fo

r pi

ping

str

ain

on p

ump

casi

ng.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-18

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A8:

C

onta

ct a

t tw

o or

mor

e hi

gh s

pots

Sea

t is

dist

orte

d m

echa

nica

lly, t

ypic

ally

cre

atin

gtw

o la

rge

cont

act s

pots

- p

atte

rn fa

des

away

betw

een

cont

act a

reas

.

Sea

ling

ring

show

s ex

celle

nt c

ondi

tion

afte

rsh

ort s

tatic

and

dyn

amic

test

s. P

ossi

ble

wire

draw

ing

eros

ion

of th

e se

alin

g rin

g if

it re

mai

nsst

atio

nary

. P

ossi

ble

wire

bru

shin

g er

osio

n if

the

seal

ing

ring

rota

tes

beca

use

out-

of-f

lat m

atin

gsu

rfac

e al

low

s di

rt to

ent

er th

e se

al a

rea.

Sea

l lea

ks s

tead

ily w

hen

the

shaf

t is

rota

ting

orst

atio

nary

.

Cau

se

Sea

l fac

es n

ot fl

at.

Ch

ecks

x

Che

ck fo

r se

al p

late

dis

tort

ion

beca

use

ofov

er-t

orqu

ing

of b

olts

.

x

Che

ck fl

atne

ss o

f fac

es u

sing

opt

ical

flat

.

x

Che

ck s

quar

enes

s of

par

ts u

sed

to c

lam

pse

at.

x

Che

ck s

eal c

ham

ber f

ace

flatn

ess

of s

plit

case

pum

ps.

x

Che

ck th

at th

e se

al p

late

sur

face

in c

onta

ctw

ith th

e se

at is

free

from

nic

ks/b

urrs

and

show

s a

full

patte

rn w

hen

blue

d w

ith th

ese

at.

A9:

C

onta

ct th

roug

h 27

0°S

eal i

s di

stor

ted

mec

hani

cally

giv

ing

cont

act

thro

ugh

appr

oxim

atel

y 27

0° w

ith th

e pa

ttern

fadi

ng a

way

at t

he lo

w s

pot.

Sea

ling

ring

show

s sa

me

sym

ptom

s as

for

mec

hani

cal d

isto

rtio

n ab

ove.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

rota

ting

orst

atio

nary

.

Cau

se

Sea

l fac

es n

ot fl

at.

Ch

eck

Che

ck fo

r se

al p

late

dis

tort

ion

beca

use

of o

ver-

torq

uing

of b

olts

.

Rem

edia

l Act

ion

s

x

Cha

nge

to a

sof

ter

gask

et m

ater

ial b

etw

een

the

seal

cha

mbe

r an

d th

e se

al p

late

.

x

Pro

vide

full

face

gas

ket c

onta

ct o

r co

ntac

tab

ove

cent

erlin

e of

bol

ts to

pre

vent

ben

ding

of th

e se

al p

late

.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-19

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A10

: Con

tact

at g

land

bol

t loc

atio

nsS

eal i

s di

stor

ted

mec

hani

cally

giv

ing

high

spo

tsat

eac

h bo

lt lo

catio

n.

Sea

ling

ring

in g

ood

cond

ition

as

initi

al le

akag

eis

hig

h, p

reve

ntin

g an

y lo

ng-t

erm

ser

vice

life

.S

eal l

eaks

ste

adily

whe

n th

e sh

aft i

s st

atio

nary

or r

otat

ing.

Cau

se

Sea

l fac

es n

ot fl

at.

Ch

eck

Che

ck fo

r se

al p

late

dis

tort

ion

beca

use

of o

ver-

torq

uing

of b

olts

.

Rem

edia

l Act

ion

s

x

Cha

nge

to a

sof

ter

gask

et m

ater

ial b

etw

een

the

seal

cha

mbe

r an

d th

e se

al p

late

.

x

Pro

vide

full

face

gas

ket c

onta

ct o

r co

ntac

tab

ove

cent

erlin

e of

bol

ts to

pre

vent

ben

ding

of th

e se

al p

late

.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-20

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A11

:F

ract

ure

Bro

ken

seal

rin

gs o

r cr

acke

d se

al r

ings

(if

reta

ined

in s

ome

asse

mbl

y).

Man

y se

al fa

cem

ater

ials

are

brit

tle a

nd r

elat

ivel

y th

in s

ectio

nsar

e fr

agile

.

Non

-uni

form

dis

colo

ratio

n or

par

tial d

isco

lora

tion

of th

e fr

actu

re s

urfa

ce o

f the

pre

senc

e of

wea

rde

bris

indi

cate

s fr

actu

re p

rior

to o

r du

ring

seal

oper

atio

n. I

f no

wea

r de

bris

is p

rese

nt, t

hefr

actu

re p

roba

bly

occu

rred

dur

ing

disa

ssem

bly.

Fra

ctur

es c

ause

d by

exc

essi

ve fa

ce to

rque

gene

rally

em

anat

e fr

om o

ne o

r m

ore

poin

ts o

fdr

ive

enga

gem

ent a

nd a

lso

show

wea

r or

dam

age

on m

atin

g dr

ive

devi

ce.

Thi

s pr

oble

mca

n oc

cur

whe

n P

TF

E O

-rin

gs a

re u

sed

to s

eal

a pi

nned

sta

tiona

ry c

arbo

n se

at w

ithou

t a b

uffe

rsl

eeve

ove

r th

e pi

n. I

n th

is c

ase,

it c

an r

esul

t in

a se

vere

gou

ge e

man

atin

g fr

om th

e pi

n sl

otra

ther

than

rin

g fr

actu

re.

Sea

l lea

ks s

tead

ilyw

hen

the

shaf

t is

stat

iona

ry o

r ro

tatin

g. W

hen

brok

en p

arts

are

wel

l ret

aine

d th

e am

ount

of

leak

age

can

som

etim

es b

e re

mar

kabl

y lo

w.

Cau

se

Pos

sibi

litie

s in

clud

e th

e fo

llow

ing:

x

Mis

hand

ling

befo

re o

r du

ring

asse

mbl

y.

x

Impr

oper

sea

l ass

embl

y or

inst

alla

tion.

x

Exc

essi

ve fa

ce to

rque

:

�

Jam

min

g fr

om im

prop

er a

ssem

bly.

�

Fai

lure

of a

xial

hol

ding

dev

ices

,ex

cess

ive

fluid

pre

ssur

e, p

oor

lubr

icat

ion.

�

Exc

essi

ve fl

uid

pres

sure

.

�

Poo

r lu

bric

atio

n.

�

Cor

rosi

on a

t sea

l fac

es.

�

Pin

sle

eve

of P

TF

E n

ot fi

tted

asre

com

men

ded

by s

eal m

aker

s.

x

Exc

essi

ve h

ydra

ulic

pre

ssur

e.

x

Exc

essi

ve s

wel

l of c

onfin

ed s

econ

dary

sea

ls.

x

Dam

age

durin

g se

al r

emov

al a

nddi

sass

embl

y.

x

Exc

essi

ve th

erm

al s

tres

s fr

om th

erm

al s

hock

or e

xces

sive

gra

dien

ts (

see

The

rmal

dist

ress

, A17

-A19

bel

ow).

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-21

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A12

:S

crat

ches

and

chi

psS

crat

ches

in th

e ra

dial

dire

ctio

n us

ually

giv

e a

leak

reg

ardl

ess

of d

epth

or

wid

th.

In o

ther

dire

ctio

ns, s

crat

ches

less

than

1P

m d

eep

by25P

m w

ide

do n

ot ty

pica

lly c

ause

ext

ensi

vele

akag

e.

Scr

atch

es a

nd n

icks

are

ofte

n er

rone

ousl

y ci

ted

as a

cau

se o

f se

al fa

ilure

and

it h

elps

to d

ecid

eif

the

scr

atch

was

cau

sed

befo

re, d

urin

g, o

raf

ter

oper

atio

n. I

f the

wea

r pa

ttern

is a

ltere

d by

the

scra

tch,

then

the

scra

tch

occu

rred

bef

ore

ordu

ring

oper

atio

n. I

f the

sam

e sc

ratc

h ex

tend

sou

tsid

e th

e m

atin

g ar

ea, i

t is

mor

e lik

ely

to h

ave

occu

rred

prio

r to

ope

ratio

n. I

f it d

oes

not e

xten

dou

tsid

e th

e m

atin

g ar

ea, a

nd is

spi

ral i

n fo

rmre

lativ

e to

the

shaf

t axi

s an

d in

the

dire

ctio

n of

rota

tion,

it p

roba

bly

occu

rred

dur

ing

oper

atio

nan

d ca

n be

attr

ibut

ed to

a p

artic

le e

nter

ing

orco

min

g fr

om th

e se

al fa

ces.

Scr

atch

es th

atin

terr

upt,

but d

o no

t alte

r, th

e w

ear

patte

rn, w

ere

prob

ably

pro

duce

d af

ter

seal

ope

ratio

n.

Chi

ps a

re u

sual

ly a

t sea

l fac

e ed

ges

and

seve

rech

ippi

ng is

sim

ilar

to th

at c

ause

d by

exc

essi

vehy

drau

lic d

isto

rtio

n.

Leak

age

rate

dep

ends

on

the

degr

ee o

f dam

age

and

mig

ht b

e re

duce

d w

hen

the

shaf

t is

stat

iona

ry.

Cau

se

Pos

sibi

litie

s in

clud

e th

e fo

llow

ing:

x

Mis

hand

ling

durin

g m

anuf

actu

re, s

tora

ge,

asse

mbl

y, o

r in

stal

latio

n.

x

Dirt

trap

ped

betw

een

seal

fac

es.

x

Edg

e ch

ippi

ng fr

om s

lam

min

g to

geth

erdu

ring

oper

atio

n w

hen

pum

p ca

vita

tes

orflu

id v

apor

izes

at s

eal f

aces

.

Ch

ecks

x

Edg

e ch

ippi

ng c

an a

lso

occu

r fr

om th

efo

llow

ing:

x

Exc

essi

ve s

haft

run

out.

x

Exc

essi

ve s

haft

defle

ctio

n or

whi

p.

x

Out

of s

quar

e se

al f

aces

.

x

(The

se c

ondi

tions

als

o ca

use

exce

ssiv

ew

ear

of th

e dr

ive

mec

hani

sm.)

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-22

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A13

:A

dhes

ive

wea

rA

com

bina

tion

of m

ild a

dhes

ive/

abra

sive

wea

r is

the

norm

al w

ay s

eals

wea

r ou

t ove

r a

long

serv

ice

life

(see

pro

per

cont

act p

atte

rn, A

1).

Exc

essi

ve a

dhes

ive

wea

r le

aves

typi

cal n

on-

met

allic

sea

l fac

es h

eavi

ly w

orn

with

a r

elat

ivel

ysm

ooth

app

eara

nce

and

a m

inim

um o

fgr

oovi

ng.

Sev

ere

adhe

sive

wea

r of

met

allic

face

s ca

n le

ad to

scu

ffing

, gro

ovin

g, a

nd e

ven

face

sei

zure

.

Sea

l lea

ks w

hen

shaf

t is

rota

ting.

Whe

nst

atio

nary

, the

sea

l mig

ht h

old

or m

ight

leak

seve

rely

.

Cau

se

x

Inad

equa

te lu

bric

atio

n.

x

Exc

essi

ve s

eal c

onta

ct p

ress

ure

for

the

face

mat

eria

ls.

x

Deg

rade

d se

al fa

ce c

ondi

tions

.

Ch

ecks

x

Che

ck fo

r ex

cess

ive

loca

l tem

pera

ture

sca

used

by

inad

equa

te c

oolin

g fo

r th

e fa

cesu

rfac

e sp

eed.

x

Che

ck 28

val

ue o

f sea

l fac

e m

ater

ials

(th

ism

etho

d ha

s its

lim

itatio

ns: s

ee S

ectio

n 3.

7).

Rem

edia

l Act

ion

s

x

Impr

oved

sea

l lub

ricat

ing

prop

ertie

s ca

n be

achi

eved

by

a te

mpe

ratu

re c

hang

e.

x

Cha

ngin

g se

al f

ace

mat

eria

ls.

x

Cha

ngin

g se

al b

alan

ce.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-23

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A14

:A

bras

ive

wea

rE

xces

sive

abr

asiv

e w

ear

leav

es s

eal f

aces

seve

rely

gro

oved

and

eve

n sc

uffe

d (b

oth

met

als

and

non-

met

als)

. H

arde

r fa

ces

show

reg

ular

groo

ving

, whi

le c

arbo

n fa

ces

tend

to w

ear

less

even

ly w

ith h

eavy

sco

ring

both

acr

oss

the

face

and

in th

e di

rect

ion

of r

otat

ion.

Virt

ually

no

wea

r ta

kes

plac

e aw

ay fr

om th

e fa

ceco

ntac

t. M

ild a

bras

ive

wea

r fr

om v

ery

fine

part

icle

s gi

ves

a w

ear

patte

rn s

imila

r to

adhe

sive

wea

r.

The

key

clu

e to

abr

asiv

e w

ear

is th

e de

posi

t of

solid

s on

the

seal

face

s or

adj

acen

t to

them

.T

he s

olid

s m

ight

als

o re

sult

from

che

mic

alef

fect

s (s

ee A

20, A

21, A

22, A

23, A

24, A

25,

A26

, A27

, and

A28

bel

ow).

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Pos

sibi

litie

s in

clud

e:

x

Pum

ped

prod

uct o

r flu

sh fl

uid

cont

ains

abra

sive

mat

ter

of a

siz

eabl

e am

ount

toen

ter

betw

een

the

face

s an

d ca

use

wea

r.

x

In s

pite

of c

lean

flui

d flu

shin

g or

use

of

barr

ier

fluid

in d

ual s

eal a

rran

gem

ent,

the

seal

is c

ausi

ng in

war

d pu

mpi

ng o

f the

abra

sive

pro

cess

flui

d ac

ross

the

seal

fac

es.

The

inw

ard

pum

ping

phe

nom

enon

is c

ause

dby

larg

e an

gula

r mis

alig

nmen

ts a

ndec

cent

riciti

es b

etw

een

the

seal

fac

es.

Rem

edia

l Act

ion

s

x

Intr

oduc

e a

clea

n flo

w to

the

seal

by

usin

gfil

ters

or

cycl

one

sepa

rato

r.

x

Intr

oduc

e a

clea

n flo

w to

the

seal

from

ase

para

te s

ourc

e.

x

Inst

all h

arde

r w

ear-

resi

stin

g fa

ce m

ater

ial,

for

exam

ple,

sili

con

carb

ide,

tung

sten

car

bide

.

x

Use

dou

ble

seal

s.

x

Elim

inat

e ex

cess

ive

mis

alig

nmen

t and

ecce

ntric

ities

.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-24

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A15

:G

roov

ing

and

seve

re w

ear

Hig

h w

ear,

eve

n cr

acki

ng, o

f the

sea

t with

polis

hed

circ

umfe

rent

ial s

corin

g, d

isco

lora

tion,

and

over

-hea

ting

sym

ptom

s. M

etal

par

ts m

ight

"blu

e" w

ith h

eat o

f dr

y ru

nnin

g. E

ven

shor

tpe

riods

of

dry

runn

ing

can

form

a d

eep

wea

rgr

oove

.

The

sea

ling

ring

disp

lays

sev

ere,

thou

gh e

ven,

wea

r th

roug

hout

360

°, w

ith ITCOQRJQPG

UEQTKPI.

Sof

t car

bon

seal

rin

gs p

ossi

bly

have

edge

chi

ppin

g. H

arde

r se

alin

g rin

gs, f

orex

ampl

e, tu

ngst

en c

arbi

de, h

ave

roun

ded

edge

s. P

ossi

ble

wea

r at

any

driv

e m

echa

nism

or n

otch

es.

Oth

er o

verh

eatin

g sy

mpt

oms

mig

htbe

app

aren

t, fo

r ex

ampl

e, h

arde

ning

and

crac

king

of O

-rin

gs.

Thi

s is

ofte

n a

star

t-up

pro

blem

and

the

seal

drip

s st

eadi

ly w

hen

the

shaf

t is

stat

iona

ry o

rro

tatin

g.

0QVG

that

the

scor

ing

dam

age

can

be c

onfu

sed

with

abr

asiv

e w

ear

(see

A14

).

Cau

se

Dry

run

ning

bec

ause

of i

nsuf

ficie

nt o

r no

liqu

idbe

twee

n th

e se

al fa

ces.

Ch

ecks

x

Che

ck fo

r ad

equa

te p

rimin

g an

d se

alch

ambe

r ven

ting.

x

Che

ck p

ump

suct

ion

flow

s an

d fil

ters

.

x

Che

ck fo

r bl

ocka

ge/r

estr

ictio

n of

circ

ulat

ion

line.

x

4GOGFKCN#EVKQPU

x

If a

circ

ulat

ion

line

does

not

exi

st, r

evie

w th

ene

ed to

inst

all o

ne.

x

Incr

ease

sea

l circ

ulat

ion

flow

.

x

Rev

iew

ope

ratin

g pr

oced

ures

(se

e al

soS

ectio

n 8.

2).

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-25

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A16

:E

rosi

on o

f car

bon

ring

If th

e ca

rbon

rin

g is

on

a ro

tatin

g co

mpo

nent

,th

is r

esul

ts in

a s

culp

ture

d ap

pear

ance

with

isla

nds

of o

rigin

al m

atin

g su

rfac

e st

ill s

how

ing.

If th

e ca

rbon

is th

e st

atio

nary

com

pone

nt, t

his

form

s a

groo

ve p

artw

ay a

cros

s th

e ca

rbon

face

adja

cent

to th

e ci

rcul

atio

n in

let o

n th

e se

al p

late

.In

sev

ere

case

s, h

arde

r fa

ce m

ater

ials

suc

h as

alum

nina

can

als

o be

ero

ded

in a

sim

ilar

man

ner.

Sea

l lea

ks w

hen

the

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Cau

sed

by e

xces

sive

flow

vel

ocity

at t

he s

eal

circ

ulat

ion

inle

t, th

e ci

rcul

atio

n flo

w c

onta

inin

gab

rasi

ve m

ater

ials

, or

a co

mbi

natio

n of

thes

e.

Rem

edia

l Act

ion

s

x

Add

ing

a flo

w c

ontr

olle

r in

circ

ulat

ion

line.

x

Shr

oudi

ng th

e se

al fa

ces.

x

Inje

ctin

g th

e ci

rcul

atio

n at

sev

eral

poi

nts.

x

Met

hods

to r

educ

e ab

rasi

ve d

amag

e as

for

abra

sive

wea

r.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-26

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A17

:T

herm

al d

istr

ess

over

360

°va

poriz

atio

nH

igh

wea

r or

ther

mal

ly-d

istr

esse

d su

rfac

e (h

eat

chec

king

) th

roug

h 36

0°.

Thi

s ap

pear

s as

rad

ial

surf

ace

crac

ks, s

omet

imes

acc

ompa

nied

with

circ

ular

sco

ring

or d

isco

lora

tion

from

ove

r-he

atin

g. I

f nec

essa

ry, d

ye p

enet

rant

can

hel

p to

show

up

the

surf

ace

crac

ks.

The

car

bon

seal

ing

ring

show

s hi

gh w

ear

and

poss

ibly

ligh

t pitt

ing

lead

ing

to EQOGV t

raili

ng.

Pos

sibl

e ed

ge c

hipp

ing

of th

e se

alin

g rin

gbe

caus

e of

ope

ning

and

clo

sing

of t

he s

eal

face

s an

d al

so p

ossi

ble

wea

r of

any

driv

eno

tche

s. C

arbo

n du

st d

epos

its o

n th

eat

mos

pher

ic s

ide

of th

e se

al a

nd w

ear/

fret

ting

ofth

e sh

aft/s

leev

e at

the

seco

ndar

y se

al (

ifdy

nam

ic)

are

also

sym

ptom

s. S

eal l

eaks

stea

dily

whe

n sh

aft i

s st

atio

nary

or

rota

ting.

The

latte

r us

ually

with

sou

nd f

rom

flas

hing

or

face

pop

ping

.

Oth

er s

eal d

amag

e ca

n al

so r

esul

t, fo

r ex

ampl

e,fa

tigue

of m

etal

bel

low

s or

wea

r of

sha

ft/s

leev

eat

sec

onda

ry s

eals

(ca

lled YGFIGGVEJKPI fo

rP

TF

E w

edge

des

igns

). I

n th

e la

tter

case

,ca

rbon

pic

k-up

on

the

seco

ndar

y se

al a

nd w

ear

of th

e se

cond

ary

seal

(fo

r ex

ampl

e, a

t the

nos

eof

the

wed

ge)

mig

ht b

e ap

pare

nt.

Cau

se

Insu

ffici

ent f

ilm th

ickn

ess.

Ch

ecks

/Rem

edia

l Act

ion

s

x

Use

a n

arro

w f

ace

carb

on (

of th

e or

der

of 2

.5m

m).

x

Incr

ease

coo

ling

to fa

ces:

�

Che

ck c

ircul

atio

n lin

es f

or b

lock

age

�

Incr

ease

d ci

rcul

atio

n flo

w a

ssis

ts in

mar

gina

l situ

atio

n

x

Rev

iew

opt

ions

to a

lter

seal

cha

mbe

rpr

essu

re; o

n m

ultip

le s

tage

pum

ps th

e se

alch

ambe

r pr

essu

re m

ight

be

take

n of

f ano

ther

stag

e to

pre

vent

flas

hing

. T

he s

eal d

esig

nw

ill r

equi

re r

evie

w to

ens

ure

it is

then

not

over

-pre

ssur

ized

.

x

Rev

iew

sea

l des

ign

and

seal

mat

eria

lse

lect

ion,

for

exam

ple,

use

a s

eal d

esig

n no

tre

quiri

ng s

o m

uch

prod

uct t

empe

ratu

rem

argi

n ('

T).

x

Use

sea

l des

ign

with

enh

ance

d fa

celu

bric

atio

n fe

atur

es, f

or e

xam

ple,

coo

ling

notc

hes,

hyd

ropa

ds, l

aser

text

ured

face

s.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-27

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A18

:T

herm

al d

istr

ess

over

120

to 1

80°

The

rmal

ly-d

istr

esse

d (h

eat-

chec

ked)

are

aap

prox

imat

ely

one-

third

of t

he c

onta

ct p

atte

rn.

Dis

tres

sed

area

180

° fr

om in

let o

f sea

l flu

sh w

ithgo

od c

onta

ct p

atte

rn a

t flu

sh in

let.

Hig

h se

alin

g rin

g w

ear

with

pos

sibl

e ca

rbon

depo

sits

on

the

atm

osph

eric

sid

e of

the

seal

.A

lso

poss

ible

wea

r at

any

driv

e m

echa

nism

notc

hes.

Sea

l drip

s st

eadi

ly w

hen

shaf

t is

rota

ting

orst

atio

nary

– p

ossi

ble

soun

d fr

om fl

ashi

ng o

rfa

ce p

oppi

ng.

Cau

se

Sea

led

liqui

d va

poriz

ing

180°

from

the

seal

flus

h.

Ch

ecks

x

Che

ck fo

r ad

equa

te c

lear

ance

s ar

ound

the

seal

fac

e to

giv

e su

ffici

ent f

ace

lubr

icat

ion

and

cool

ing.

x

Che

ck th

at s

eal c

ham

ber

neck

bus

hcl

eara

nce

is c

orre

ct.

Rem

edia

l Act

ion

s

x

Add

a c

ircum

fere

ntia

l flu

sh g

roov

e in

the

glan

d pl

ate.

x

Add

a ta

ngen

tial i

nlet

mat

ched

to th

e sh

aft

rota

tion

to a

id d

istr

ibut

ion.

x

See

The

rmal

Dis

tres

s O

ver

360°

(A

17).

A19

:T

herm

al d

istr

ess

in p

atch

esT

wo,

thre

e, fo

ur, f

ive,

or

six

hot s

pots

of

ther

mal

ly-d

istr

esse

d or

hea

t-ch

ecke

d su

rfac

e.T

hese

pat

ches

are

som

etim

es c

alle

d VJGTO

CN

CURGTKVKGU�

Hig

h se

alin

g rin

g w

ear

with

pos

sibl

e ca

rbon

depo

sits

on

the

atm

osph

eric

sid

e of

the

seal

.A

lso

poss

ible

wea

r at

any

driv

e m

echa

nism

notc

hes.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

rota

ting

orst

atio

nary

. Lea

kage

mig

ht b

e in

the

form

of

vapo

r an

d w

ith s

ound

from

flas

hing

or f

ace

popp

ing.

Cau

se

Sea

led

liqui

d va

poriz

ing

betw

een

the

seal

face

s.F

ailu

re fr

om h

ot s

pots

is m

ore

likel

y to

occ

ur o

nlig

ht s

peci

fic-g

ravi

ty li

quid

s at

hig

h sp

eeds

and

pres

sure

s.

Ch

ecks

x

Che

ck fo

r ad

equa

te c

oolin

g of

sea

l fac

es.

x

Che

ck fo

r se

at d

isto

rtio

n.

Rem

edia

l Act

ion

s

x

Incr

ease

coo

ling

of s

eal f

aces

.

x

Rev

iew

pos

sibi

lity

of s

eal i

nter

face

coo

ling

with

the

seal

man

ufac

ture

r.

x

See

The

rmal

Dis

tres

s O

ver

360°

(A

17).

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-28

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A20

:C

okin

gT

his

usua

lly o

ccur

s w

ith h

ydro

carb

on p

rodu

cts

at h

igh

tem

pera

ture

s. It

is in

dica

ted

by fa

ilure

of

the

seal

to fo

llow

up,

that

is, n

o sl

idin

g ac

tion.

Thi

s ca

n be

foun

d af

ter

rem

oval

of t

he s

eal p

late

durin

g th

e st

ripdo

wn

for

insp

ectio

n. C

oke

part

icle

s co

llect

on

the

insi

de o

f the

slid

ing

mem

ber,

eve

n to

the

exte

nt w

here

it c

an b

edi

fficu

lt to

rem

ove.

In m

any

case

s of

con

tinuo

usop

erat

ion,

hea

t fro

m th

e pr

oduc

t and

sea

lfr

ictio

n ca

n ke

ep th

e co

ke a

nd a

ssoc

iate

dw

axes

and

gum

s re

ason

ably

sof

t and

the

seal

will

ope

rate

sat

isfa

ctor

ily.

Leak

age

typi

cally

occ

urs

on s

tart

-up

afte

r a

perio

d of

shu

t-do

wn

or o

n st

andb

y w

hen

solid

ifica

tion

of w

axes

/gum

s as

soci

ated

with

the

coke

par

ticle

s ta

kes

plac

e. T

he le

akag

e ca

n in

odd

case

s re

duce

aft

er a

sho

rt p

erio

d of

run

ning

as th

ese

wax

es s

ofte

n.

Cau

se

Min

ute

quan

titie

s of

leak

age

carb

oniz

ing

on th

eat

mos

pher

ic s

ide

of th

e se

al c

ausi

ng th

e sl

idin

gm

embe

r to

jam

and

hen

ce n

ot fo

llow

up

any

face

wea

r.

Rem

edia

l Act

ion

s

x

The

usu

al a

ppro

ach

with

hyd

roca

rbon

s is

tofit

a p

erm

anen

t low

-pre

ssur

e st

eam

que

nch

on th

e at

mos

pher

ic s

ide

of th

e se

al to

prev

ent t

he b

uild

-up

and

solid

ifica

tion

of c

oke

and

wax

par

ticle

s. A

n ad

equa

tely

siz

ed d

rain

will

bot

h pr

even

t exc

essi

ve s

team

pre

ssur

ean

d as

sist

par

ticle

rem

oval

. Thi

s qu

ench

mus

t be

oper

atio

nal b

efor

e st

art-

up.

x

If no

t alre

ady

fitte

d, a

hig

h-te

mpe

ratu

re li

pse

al a

t the

bac

k of

the

seal

pla

te im

prov

esqu

ench

ing

effic

ienc

y. It

als

o re

duce

s th

elik

elih

ood

of s

team

ent

erin

g th

e be

arin

gho

usin

g.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-29

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A21

:C

arbo

n ch

emic

al a

ttack

Are

a of

car

bon

ring

in c

onta

ct w

ith th

e pr

oduc

t is

corr

osiv

ely

atta

cked

, res

ultin

g in

ove

rall

mat

eria

lre

mov

al, p

ittin

g, p

oros

ity, s

ofte

ning

, or

disi

nteg

ratio

n.

Ess

entia

lly, t

here

are

two

carb

on-g

raph

iteco

rros

ion

mod

es: o

vera

ll co

rros

ion

and

sele

ctiv

ele

achi

ng.

Ove

rall

corr

osio

n oc

curs

whe

n it

is a

ttack

ed b

yhi

ghly

oxi

dizi

ng a

cids

or

high

ly c

once

ntra

ted

caus

tic fl

uids

. A h

ardn

ess

redu

ctio

n of

20

Sho

resc

lero

scop

e po

ints

is ty

pica

l for

car

bon-

grap

hite

mat

eria

ls th

at h

ave

been

che

mic

ally

atta

cked

. In

seve

re c

ases

of

this

type

, sea

l fac

es a

rere

duce

d to

slu

dge.

Sel

ectiv

e le

achi

ng o

f the

impr

egna

nt (

adde

d to

the

othe

rwis

e po

rous

car

bon

to m

ake

itim

perv

ious

) re

sults

in e

ither

incr

ease

d w

ear

rate

or s

eal f

ace

poro

sity

. With

this

mec

hani

sm, a

hard

ness

red

uctio

n of

5 S

hore

scl

eros

cope

poin

ts is

typi

cal f

or c

arbo

n-gr

aphi

te m

ater

ials

.P

ress

ure

test

ing

for

poro

sity

can

als

o be

use

d to

conf

irm s

uch

a pr

oble

m.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Inco

mpa

tibili

ty o

f the

car

bon

with

the

prod

uct,

resu

lting

in tw

o fa

ilure

mec

hani

sms.

x

Ove

rall

corr

osio

n.

x

Sel

ectiv

e le

achi

ng o

f im

preg

nant

.

Rem

edia

l Act

ion

s

A c

hang

e of

mat

eria

l – b

oth

failu

re m

echa

nism

sre

quire

che

ckin

g th

e m

ater

ial s

elec

tion

for

prod

uct c

ompa

tibili

ty a

nd th

e or

igin

al p

rodu

ctco

nditi

ons

agai

nst t

he s

eal s

elec

tion.

A c

orro

sion

rat

e of

0.0

25 m

m (

0.00

1 in

.) p

er y

ear

is n

orm

ally

qui

te u

nacc

epta

ble

for

seal

s, e

ven

thou

gh th

is is

sat

isfa

ctor

y fo

r m

ost i

ndus

tria

lha

rdw

are.

It is

usu

ally

, the

refo

re, b

ette

r to

use

seal

man

ufac

ture

r da

ta th

an a

ny n

on-n

umer

ical

indu

stria

l cor

rosi

on d

ata

whe

n as

sess

ing

such

apr

oble

m.

Man

y hi

ghly

cor

rosi

ve p

rodu

cts,

for

exam

ple,

oleu

m, p

rese

nt a

con

flict

bet

wee

n co

rros

ion

and

wea

r re

sist

ance

of t

he fa

ce m

ater

ials

, whi

ch,

even

with

the

late

st m

ater

ials

, res

ults

in a

max

imum

sea

l life

of o

nly

a fe

w m

onth

s.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-30

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A22

:C

orro

sion

of m

etal

face

sC

orro

sive

atta

ck b

y th

e pr

oduc

t, se

alan

t, or

atm

osph

ere.

Cor

rosi

on is

acc

eler

ated

bec

ause

the

face

is s

ubje

ct to

slid

ing

cont

act w

ear.

Dis

sim

ilar

mat

eria

ls c

an a

lso

set u

p an

elec

trol

ytic

cor

rosi

ve a

ctio

n.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Man

y co

rros

ion

failu

re m

echa

nism

s su

ch a

sov

eral

l cor

rosi

on, i

nter

gran

ular

cor

rosi

on, s

tres

sco

rros

ion

crac

king

, etc

., oc

cur

in m

echa

nica

lse

als.

Rem

edia

l Act

ion

s

Thi

s ca

n be

ana

lyze

d an

d so

lved

in ju

st th

esa

me

way

as

with

oth

er m

echa

nica

l dev

ices

.

A23

:C

orro

sion

of h

ard

face

sT

his

is c

omm

only

the

resu

lt of

leac

hing

of

bind

ers

or fi

llers

in a

lum

ina,

tung

sten

car

bide

,an

d si

licon

car

bide

. Cer

tain

cor

rosi

ve fl

uids

leac

h th

e bi

nder

s/fil

lers

from

thes

e ce

ram

ics

and,

in e

ffect

, con

vert

the

seal

face

into

agr

indi

ng s

urfa

ce. A

s le

achi

ng c

ontin

ues,

the

cera

mic

par

ticle

s ev

entu

ally

bec

ome

disl

odge

dfr

om th

e ba

se m

ater

ial a

nd c

ause

abr

asiv

e w

ear

of o

ne o

r bo

th s

eal f

aces

. Sea

l fac

e fla

tnes

s is

degr

aded

to th

e po

int o

f se

al fa

ilure

by

the

resu

lting

voi

ds in

the

cera

mic

sur

face

and

/or

the

abra

sive

dam

age.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

In ty

pica

l com

mer

cial

alu

min

a (7

5 or

85%

), th

eal

umin

a pa

rtic

les

are

bond

ed to

geth

er b

y a

pred

omin

antly

sili

ca g

lass

bin

der.

Sea

led

fluid

sw

ith a

pH

gre

ater

than

10,

or

cont

aini

nghy

drof

luor

ic a

cid,

leac

h ou

t thi

s bi

nder

, giv

ing

the

failu

re c

hara

cter

istic

s de

scrib

ed.

Cer

tain

gra

des

of s

ilico

n ca

rbid

e co

ntai

n fr

eesi

licon

that

can

be

sim

ilarly

atta

cked

(fo

rex

ampl

e, b

y hy

drof

luor

ic a

cid)

.

Aci

dic

fluid

s m

ight

leac

h ni

ckel

or

coba

lt bi

nder

sin

corp

orat

ed in

cem

ente

d tu

ngst

en c

arbi

de,

agai

n gi

ving

the

failu

re c

hara

cter

istic

s de

scrib

ed.

Rem

edia

l Act

ion

s

99.5

% a

lum

ina,

sili

con-

free

sili

con

carb

ide

(som

etim

es c

alle

d UKPVGTG

FCNRJC),

and

allo

y-bo

nded

tung

sten

car

bide

that

with

stan

d su

chflu

ids

mor

e ef

fect

ivel

y ar

e no

w a

vaila

ble.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-31

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A24

:F

laki

ng a

nd p

eelin

g(o

f har

d co

atin

gs)

Sta

inle

ss s

teel

sea

l fac

es a

re u

sual

ly p

late

d w

itha

hard

-fac

ing

of S

telli

te, c

eram

ic, t

ungs

ten

carb

ide,

or

a va

riety

of

othe

r m

ater

ials

.

The

failu

re o

ften

sta

rts

with

slig

ht b

liste

ring,

then

liftin

g of

the

coat

ing.

Fin

al fa

ilure

mig

ht w

ell b

eac

cele

rate

d by

abr

asiv

e w

ear

of o

ne o

r bo

thse

al f

aces

by

hard

par

ticle

s as

they

bec

ome

disl

odge

d fr

om th

e co

atin

g.

Sea

l lea

kage

can

esc

alat

e qu

ickl

y an

dco

ntin

ues

whe

n th

e sh

aft i

s st

oppe

d.

Cau

ses

Pos

sibi

litie

s ar

e:

x

A d

efec

tive

coat

ing

x

Che

mic

al a

ttack

at t

he b

ond

betw

een

the

base

met

al a

nd th

e co

atin

g.

Ch

ecks

The

che

mic

al a

ttack

mig

ht b

e ag

grav

ated

by

both

hea

t gen

erat

ion

at th

e se

al fa

ce a

nd th

epo

rosi

ty in

here

nt in

som

e co

atin

g te

chni

ques

.

Rem

edia

l Act

ion

s

Cha

ngin

g to

a s

olid

face

mat

eria

l is

the

usua

lso

lutio

n ad

opte

d.

A25

: Cry

stal

lizat

ion

Sim

ilar

sym

ptom

s as

for

Cok

ing

(A20

), e

xcep

tth

at it

occ

urs

on v

ario

us p

rodu

cts

and

cond

ition

s. S

omet

imes

the

crys

tals

em

bed

in th

eso

fter

face

and

rap

idly

abr

ade

the

hard

er fa

ce.

Not

e th

at a

s w

ell a

s fr

om th

e pr

oduc

t, cr

ysta

lsca

n co

me

from

the

atm

osph

ere

(for

exa

mpl

e,ic

e cr

ysta

ls)

or fr

om a

bar

rier

fluid

(fo

r ex

ampl

e,ha

rd w

ater

dep

osit)

.

Leak

age

rate

s va

ry w

idel

y.

Cau

se

A b

uild

-up

of c

ryst

als

from

the

pum

ped

prod

uct

givi

ng b

oth

high

Abr

asiv

e W

ear

Rat

es (

A14

) or

failu

re to

follo

w u

p (C

okin

g, A

20, a

nd S

eal H

ang-

up, C

6).

Rem

edia

l Act

ion

s

As

with

cok

ing,

the

best

rem

edy

is a

per

man

ent

quen

ch to

dis

solv

e or

dis

pers

e th

e cr

ysta

ls.

Exa

mpl

es o

f qu

ench

flui

ds a

re h

ot w

ater

, ste

am,

and

solv

ent,

acco

rdin

g to

the

prod

uct.

Aga

in, l

ipse

al im

prov

es q

uenc

h ef

ficie

ncy.

The

cry

stal

s ca

n co

me

from

the

atm

osph

ere,

for

exam

ple,

ice

on L

PG

pum

p du

ties,

whe

re a

nitr

ogen

que

nch

to k

eep

moi

stur

e fr

om th

e se

alis

one

pos

sibl

e ap

proa

ch.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-32

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A26

:S

ludg

ing

A p

olis

hed

wea

r tr

ack

or s

light

sco

ring

on th

eha

rd f

ace.

Sm

all c

avity

hol

es o

n th

e ca

rbon

face

(fro

m w

hich

par

ticle

s ha

ve b

een

pulle

d).

Pos

sibl

e di

stor

tion

of th

e dr

ive

sprin

g or

exce

ssiv

e w

ear/

dam

age

on o

ther

driv

em

echa

nism

s.

Ass

ocia

ted

with

the

seal

ing

of h

igh

visc

osity

liqui

ds, p

artic

ular

ly a

cute

on

pum

ps s

ealin

ghy

droc

arbo

n liq

uids

at t

empe

ratu

res

abov

eam

bien

t. W

hen

shut

dow

n, th

e vi

scos

ity o

f the

pum

ped

liqui

d an

d th

e in

terf

ace

film

incr

ease

sas

the

tem

pera

ture

dro

ps a

nd p

robl

ems

mig

htar

ise

on r

esta

rtin

g th

e pu

mp.

Onc

e le

akag

e oc

curs

afte

r st

art-

up, i

t sel

dom

stop

s w

hen

the

pum

p is

sto

pped

aga

in.

Cau

se

The

she

ar s

tres

ses

betw

een

the

seal

face

sex

ceed

the

rupt

ure

stre

ngth

of t

he c

arbo

n an

dpa

rtic

les

are

pulle

d fr

om th

e ca

rbon

face

. Thi

s is

usua

lly b

ecau

se o

f a

visc

osity

incr

ease

whe

nsh

ut d

own,

but

it a

lso

occu

rs w

hen

the

inte

rfac

efil

m p

artia

lly c

arbo

nize

s fr

om o

verh

eatin

g.

Ch

ecks

x

Ens

ure

visc

osity

ran

ge o

f pr

oduc

ts is

with

inse

al c

apab

ilitie

s.

x

Che

ck th

at p

ump

heat

is a

dequ

ate

to g

ive

prod

uct c

ircul

atio

n ar

ound

the

seal

are

aun

der

pum

ping

con

ditio

ns.

Rem

edia

l Act

ion

s

x

To

over

com

e st

art-

up p

robl

ems:

•P

rehe

at c

ircul

atio

n lin

es (

for

exam

ple,

by s

team

trac

king

).

•P

rehe

at s

eal a

rea

(for

exa

mpl

e, lo

wpr

essu

re s

team

to s

eal c

ham

ber

jack

et/tr

acin

g).

•P

rehe

at s

eal f

aces

(fo

r ex

ampl

e, lo

w-

pres

sure

ste

am q

uenc

h).

Suc

h he

atin

g to

be

used

for

15

– 30

min

utes

prio

r to

sta

rt-u

p.

x

Sup

ply

cont

inuo

us h

eat t

hrou

gh a

hea

ted

seal

pla

te.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-33

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

A27

:B

ondi

ngS

imila

r ph

enom

enon

to S

ludg

ing

(A26

). In

this

situ

atio

n, a

bon

d is

form

ed b

etw

een

the

two

seal

face

s af

ter

the

pum

p ha

s be

en s

tatio

nary

for

alo

ng p

erio

d. O

n st

artin

g, p

artic

les

are

pulle

dfr

om th

e ca

rbon

face

and

leak

age

occu

rs.

The

app

eara

nce

of th

e se

al a

nd o

ther

sym

ptom

s ar

e si

mila

r to

that

from

slu

dgin

gpr

oble

ms.

Onc

e le

akag

e oc

curs

afte

r st

art-

up, i

t sel

dom

stop

s w

hen

the

pum

p is

sto

pped

aga

in.

Cau

se

The

mai

n ca

use

is w

hen

a pu

mp

is te

sted

on

adi

ffer

ent l

iqui

d to

that

on

whi

ch it

will

ope

rate

and

a ch

emic

al r

eact

ion

occu

rs b

etw

een

the

test

flui

dfil

m a

nd th

e ac

tual

pro

duct

film

.

Rem

edia

l Act

ion

s

x

Sel

ectio

n of

sui

tabl

e te

st fl

uid.

x

Ope

ratio

n on

an

inte

rmed

iate

flus

hing

flui

dfo

r a

shor

t per

iod

betw

een

test

ing

and

prod

uctio

n us

e.

A28

:B

liste

ring

Sim

ilar

phen

omen

on to

Slu

dgin

g (A

26)

and

Bon

ding

(A

27).

Initi

ally

, thi

s fa

ilure

app

ears

as

a sh

iny

brui

sed

effe

ct in

the

surf

ace

and,

at a

late

r st

age,

man

ifest

s its

elf a

s a

crat

er w

here

the

brui

se h

asde

tach

ed it

self

from

the

surf

ace

and

pass

edth

roug

h th

e se

al fa

ces.

Nor

mal

ly a

ssoc

iate

d w

ith s

tart

-sto

p ap

plic

atio

ns.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

rota

ting

orst

atio

nary

.

Cau

se

Hig

h lo

cal h

eatin

g oc

curs

in a

few

sec

onds

on

star

t-up

, par

ticul

arly

with

hig

h vi

scos

ity p

rodu

cts

in h

igh

spee

d, m

otor

-driv

en p

umps

ope

ratin

g at

high

pre

ssur

e. T

his

heat

ing

can

caus

e ra

pid

expa

nsio

n of

liqu

id th

at h

as b

een

abso

rbed

into

the

seal

face

sur

face

. Thi

s ra

pid

expa

nsio

nca

uses

hig

h st

ress

whi

ch, i

n ex

trem

e ca

ses,

exce

eds

the

rupt

ure

stre

ngth

of m

ater

ial.

Rem

edia

l Act

ion

s

Diff

icul

t pro

blem

to s

olve

; use

ful a

ppro

ache

sin

clud

e th

e fo

llow

ing:

x

Kee

ping

pro

duct

vis

cosi

ty lo

w b

y he

atin

g.

x

Car

eful

cho

ice

of s

eal m

ater

ials

. One

s w

ithhi

gher

ther

mal

con

duct

ivity

pro

duce

less

blis

terin

g ag

ains

t car

bon

coun

terf

aces

.C

erta

in g

rade

s of

car

bon-

grap

hite

are

mor

ere

sist

ant.

x

Rev

iew

of s

tart

-up

proc

edur

es.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-34

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

Com

mon

Sea

l Fai

lure

Mod

es –

Sec

onda

ry S

eals

B1:

Phy

sica

l dam

age

Cut

s, s

crat

ches

, nic

ks, o

r te

ars

in O

-rin

gs,

bello

ws,

wed

ges,

and

oth

er s

econ

dary

sea

ls.

Pla

stic

sea

ls, f

or e

xam

ple,

PT

FE

, pos

sess

less

elas

tic s

elf-

heal

ing

prop

ertie

s th

an e

last

omer

icse

cond

ary

seal

s.

All

form

s of

bel

low

s, r

ubbe

r, P

TF

E, a

nd m

etal

,ca

n ea

sily

be

dam

aged

and

the

loca

tion

mig

htno

t be

easy

to s

pot.

Sea

l drip

s st

eadi

ly w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Pos

sibi

litie

s in

clud

e:

x

Mis

hand

ling.

x

Inad

equa

te in

stal

latio

n pr

actic

e.

x

Pre

senc

e of

dirt

.

x

Fai

lure

to r

emov

e bu

rrs,

sha

rp e

dges

of

step

s, k

eyw

ays,

hol

es, e

tc.,

and

prev

ious

set

scre

w in

dent

atio

ns p

rior

to s

eal i

nsta

llatio

n.

x

Bel

low

s da

mag

e ca

n al

so b

e ca

used

by

man

ufac

turin

g de

fect

s–in

clus

ions

, inc

orre

ctcu

ring,

inad

equa

te w

eld

qual

ity, a

nd s

o on

.

Rem

edia

l Act

ion

s

Hav

ing

foun

d th

e ca

use,

the

only

usu

alre

ctifi

catio

n of

the

seco

ndar

y se

al d

amag

e is

rene

wal

.

B2:

Ext

rusi

onT

his

can

occu

r w

ith O

-rin

gs, w

edge

s, b

ello

ws,

and

othe

r se

cond

ary

seal

s. T

he m

ost c

omm

onfo

rm is

O-r

ing

extr

usio

n an

d th

is o

ccur

s w

hen

part

of t

he O

-rin

g is

forc

ed th

roug

h cl

ose

clea

ranc

e ga

ps. T

ypic

ally

, a li

p is

firs

t for

med

on

the

O-r

ing;

it is

then

cut

and

, in

som

e ca

ses,

peel

ed o

ff li

ke a

n ou

ter

cove

r.

Fla

ying

or

shre

ddin

g is

mos

t com

mon

on

synt

hetic

rub

ber

rings

, whe

reas

a li

p is

usu

ally

form

ed o

n V

iton

or P

TF

E. T

herm

opla

stic

mat

eria

ls, f

or e

xam

ple,

PT

FE

and

Vito

n, a

rem

ore

susc

eptib

le to

ext

rusi

on a

t ele

vate

dte

mpe

ratu

res.

Sea

l lea

kage

mig

ht r

educ

e w

hen

shaf

t is

stop

ped.

Cau

se

Pos

sibi

litie

s in

clud

e:

x

Use

of

exce

ssiv

e fo

rce

whe

n fit

ting

and

asse

mbl

ing

com

pone

nts.

x

Exc

essi

ve p

ress

ure

(pos

sibl

y ag

grav

ated

by

over

heat

ing

and

chem

ical

inco

mpa

tibili

ty).

x

Inco

rrec

t sha

ft a

nd/o

r O

-rin

g gr

oove

siz

ing

givi

ng e

xces

sive

cle

aran

ce b

etw

een

com

pone

nts.

Rem

edia

l Act

ion

s

As

wel

l as

chec

king

the

abov

e, o

ther

cha

nges

can

be m

ade,

suc

h as

fitti

ng a

bac

k-up

rin

g, a

chan

ge o

f se

al d

esig

n, a

cha

nge

of m

ater

ial,

and

so o

n.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-35

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

B3:

Exc

essi

ve to

rque

Som

e se

cond

ary

seal

s pr

ovid

e a

driv

e fu

nctio

n;ex

ceed

ing

the

torq

ue c

apac

ity w

ill c

ause

prob

lem

s. T

ypic

ally

this

will

eith

er in

volv

e (1

)ro

tatio

nal m

ovem

ent r

esul

ting

in w

ear

orul

timat

e fa

ilure

of

seal

from

fric

tiona

l hea

tde

velo

ped

durin

g sl

idin

g co

ntac

t, or

(2)

exce

edin

g th

e st

ruct

ural

torq

ue c

apac

ity o

f the

devi

ce. A

n ex

ampl

e of

(1)

is r

otat

ion

of a

sea

tde

pend

ent o

n fr

ictio

n of

its

O-r

ing

to a

void

rota

tion

(no

anti-

rota

tion

pin)

. An

exam

ple

of (

2)is

bel

low

s to

rsio

nal f

ailu

re. T

his

can

give

ver

yla

rge

seal

leak

s.

The

pho

togr

aph

show

s a

met

al b

ello

ws

failu

re(r

ubbe

r be

llow

s te

ar in

a s

imila

r man

ner)

. Thi

sca

n be

com

pare

d w

ith b

ello

ws

over

-pr

essu

rizat

ion,

whi

ch c

an a

lso

rupt

ure

the

bello

ws.

Cau

se

Pos

sibi

litie

s in

clud

e:

x

Bon

ding

of

a hi

gh v

isco

sity

film

bet

wee

n th

ese

al f

aces

(A

27).

On

star

t-up

, the

bon

dst

reng

th is

gre

ater

than

the

desi

gn to

rque

capa

city

of t

he s

eal.

x

Hig

h se

al fa

ce fr

ictio

n, fo

r ex

ampl

e, fr

om la

ckof

lubr

icat

ion.

Rem

edia

l Act

ion

s

If th

e ca

use

cann

ot b

e re

ctifi

ed u

sing

met

hods

refe

rred

to u

nder

Slu

dgin

g (A

26),

Bon

ding

(A

27),

Adh

esiv

e W

ear

(A13

), G

roov

ing

and

Sev

ere

Wea

r (A

15),

and

The

rmal

Dis

tres

s (A

17, A

18,

A19

), m

odifi

ed s

eals

with

an

anti-

rota

tion

devi

ceap

prop

riate

to th

e pr

oble

m a

re a

vaila

ble.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-36

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

B4.

Har

d or

cra

cked

ela

stom

erR

ubbe

r O

-rin

g ha

rden

ed a

nd c

rack

ed. P

TF

E O

-rin

g di

scol

ored

blu

e/bl

ack.

The

por

tion

of th

erin

g ne

ares

t the

face

s is

usu

ally

the

wor

st. M

ost

com

mon

ly a

pro

blem

with

nitr

ile r

ubbe

r.C

ompa

rativ

e an

alys

is o

f sec

onda

ry s

eals

fro

mal

l loc

atio

ns w

ill r

evea

l whe

ther

the

ther

mal

cond

ition

was

loca

l to

one

seco

ndar

y se

al o

r an

over

all e

xces

sive

tem

pera

ture

.

It is

impo

rtan

t to

dist

ingu

ish

betw

een

chem

ical

atta

ck a

nd th

erm

al d

amag

e to

dec

ide

on th

ere

med

y. C

hem

ical

atta

ck is

mor

e lik

ely

onse

cond

ary

seal

sur

face

s ex

pose

d to

the

fluid

;th

erm

al d

egra

datio

n is

mor

e fr

eque

ntly

foun

d on

surf

aces

exp

osed

to th

e at

mos

pher

e.

Sea

l drip

s st

eadi

ly w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Tw

o po

ssib

ilitie

s: o

verh

eatin

g or

che

mic

al a

ttack

(see

als

o E

last

omer

Che

mic

al A

ttack

, B6

belo

w).

If m

ost o

r al

l dam

age

is o

n se

cond

ary

seal

surf

aces

that

con

tact

a s

eal f

ace

mem

ber,

exce

ssiv

e fr

ictio

nal h

eat f

rom

the

face

is th

elik

ely

caus

e.

Oth

er p

ossi

ble

ther

mal

dam

age

sour

ces

are:

x

Hea

t soa

k fr

om th

e se

al e

nviro

nmen

tin

clud

ing

the

shaf

t and

hou

sing

.

x

Rel

ativ

e ro

tatio

nal m

ovem

ent b

etw

een

the

seco

ndar

y se

al a

nd th

e sh

aft o

r ho

usin

g.

It is

impo

rtan

t to

iden

tify

the

sour

ce o

f th

erm

alda

mag

e as

it m

ight

lead

to th

e ro

ot c

ause

of t

hefa

ilure

. For

exa

mpl

e, e

xces

sive

load

ing

of th

ese

al f

ace

mat

eria

l cou

ld h

ave

caus

ed th

efr

ictio

nal h

eat,

and

chan

ging

the

O-r

ing

mat

eria

lw

ould

not

avo

id p

rem

atur

e fu

ture

failu

re o

f the

seal

fac

es.

Ch

ecks

x

Che

ck c

ircul

atio

n to

sea

l are

a.

x

Che

ck fo

r dr

y ru

nnin

g, lo

w p

ump

suct

ion

flow

, slu

dgin

g, a

nd s

o on

.

x

Ens

ure

any

cool

ing

is fu

lly o

pera

tiona

l.

x

Che

ck p

rodu

ct c

ondi

tions

are

as

orig

inal

lysp

ecifi

ed a

nd th

at O

-rin

g m

ater

ial i

s su

itabl

e.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-37

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

B5:

Com

pres

sion

set o

f ela

stom

erA

lthou

gh th

is w

ill o

ccur

ove

r a

perio

d of

tim

e,ea

rly c

hang

es in

sec

tion

as s

how

n w

ill r

esul

t in

prem

atur

e fa

ilure

. Com

pres

sion

set

doe

s no

tin

volv

e a

sign

ifica

nt v

olum

e ch

ange

.

Sea

l lea

ks s

tead

ily w

hen

shaf

t is

stat

iona

ry o

rro

tatin

g.

Cau

se

Exc

essi

ve te

mpe

ratu

re fo

r th

e O

-rin

g m

ater

ial.

Som

etim

es c

ause

d by

inco

mpa

tibili

ty w

ith fl

uids

.

B6:

Ela

stom

er c

hem

ical

atta

ckT

his

give

s ex

cess

ive

volu

me

chan

ge, e

ither

swel

l or

shrin

kage

, whi

ch c

ause

s a

seal

fai

lure

thro

ugh

one

or m

ore

of th

e fo

llow

ing:

x

Ext

rusi

on c

ause

d by

sw

ell.

x

Sea

l fac

e di

stor

tion

and

mis

alig

nmen

tca

used

by

swel

l.

x

Loss

of

seco

ndar

y se

al in

terf

eren

ce c

ause

dby

shr

inka

ge.

x

Shr

inka

ge o

f sea

ls g

ivin

g lo

ss o

f se

cond

ary

seal

driv

e.

Leak

age

mig

ht o

ccur

from

the

O-r

ing

bein

gea

ten

away

. It m

ight

als

o ap

pear

to h

ave

lost

its

orig

inal

com

posi

tion

and

to b

e br

eaki

ng u

p.O

ften

pro

duct

-sid

e is

bad

ly a

ttack

ed w

hile

non

-pr

oduc

t sid

e ha

s a

rela

tivel

y go

od a

ppea

ranc

e.

Leak

age

rate

s va

ry w

idel

y.

Cau

se

Che

mic

al a

ttack

of e

last

omer

by

the

prod

uct.

Ch

ecks

It is

nec

essa

ry to

che

ck th

e or

igin

al p

rodu

ctco

nditi

ons

agai

nst t

he s

eal s

elec

tion

and

ensu

reth

at th

e O

-rin

g fit

ted

is m

ade

of th

e co

rrec

tm

ater

ial.

O-r

ing/

chem

ical

inco

mpa

tibili

ty c

hart

s ar

eav

aila

ble

from

sea

l man

ufac

ture

rs. I

f the

re is

ado

ubt a

bout

a v

olum

e ch

ange

, sec

onda

ry s

eal

dim

ensi

ons

shou

ld b

e m

easu

red

in b

oth

free

and

asse

mbl

ed c

ondi

tions

and

com

pare

d w

ith th

ose

spec

ified

on

asse

mbl

y dr

awin

g. A

n op

tical

com

para

tor

is o

ne u

sefu

l ins

trum

ent f

or s

uch

O-

ring

exam

inat

ion.

Spe

cial

ly c

olor

ed O

-rin

gs to

ass

ist i

nid

entif

icat

ion

help

to e

nsur

e th

at th

e co

rrec

tm

ater

ial i

s us

ed. H

owev

er, s

ome

colo

ring

addi

tives

mig

ht h

ave

a lo

wer

cor

rosi

onre

sist

ance

than

the

base

ela

stom

er.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-38

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

B7:

Cor

rosi

on a

t sec

onda

ry s

eal

inte

rfac

esT

his

give

s a

subt

le le

akag

e pa

th r

esul

ting

from

two

diff

eren

t mec

hani

sms;

fret

ting

corr

osio

n an

dcr

evic

e co

rros

ion.

Fre

tting

cor

rosi

on is

cau

sed

by s

mal

l rel

ativ

e m

ovem

ents

bet

wee

n a

seco

ndar

y se

al a

nd it

s m

atin

g su

rfac

e. T

hede

gree

of

dam

age

is a

ccel

erat

ed in

the

pres

ence

of

even

a s

light

ly a

ggre

ssiv

e pr

oduc

t(f

or e

xam

ple,

wat

er)

and

is p

artic

ular

lyag

grav

ated

by

the

pres

ence

of c

hlor

ides

. The

fret

ting

corr

osio

n de

bris

is a

bras

ive

and

the

late

rst

ages

of

atta

ck a

re a

ssis

ted

by a

3-b

ody

abra

sive

wea

r m

echa

nism

, whe

re d

ebris

embe

ds in

the

seco

ndar

y se

al a

nd w

ears

the

shaf

t or

slee

ve.

Cre

vice

(or

oxy

gen

conc

entr

atio

n ce

ll) c

orro

sion

occu

rs b

ecau

se s

econ

dary

sea

ls, f

or e

xam

ple,

elas

tom

eric

bel

low

s, c

an tr

ap a

sm

all a

mou

nt o

fflu

id a

djac

ent t

o th

e sh

aft.

A g

ood

indi

catio

n of

this

failu

re m

ode

is a

pol

ishe

d or

gas

-scr

ubbe

dar

ea a

djac

ent t

o th

e co

rrod

ed s

ectio

n th

at is

gene

rate

d by

hyd

roge

n em

anat

ing

from

the

crev

ice,

that

is, f

rom

ben

eath

the

bello

ws.

Cau

se

Fre

tting

cor

rosi

on is

prim

arily

gov

erne

d by

mec

hani

cal f

acto

rs s

uch

as e

quip

men

t con

ditio

n,se

al a

ssem

bly

proc

edur

es, a

nd c

orre

ct m

ater

ials

sele

ctio

n.

Ch

ecks

Com

mon

con

trib

utor

s to

fret

ting

corr

osio

nin

clud

e

x

Exc

essi

ve s

haft

end

play

– o

ver

0.1

mm

(0.0

04 in

.).

x

Exc

essi

ve s

haft

defle

ctio

n –

over

0.0

8 m

m(0

-.00

3 in

.).

x

Exc

essi

ve o

ut-o

f-sq

uare

ness

of

seal

face

tosh

aft a

xis

– ov

er 0

.08

mm

(0.

003

in)

Tot

alIn

dica

ted

Run

out (

TIR

).

Fre

tting

cor

rosi

on is

mos

t com

mon

at t

hedy

nam

ic s

econ

dary

sea

l und

er a

pus

her

type

seal

(fo

r w

hich

the

abov

e va

lues

ref

er).

In a

push

er ty

pe s

eal,

the

seco

ndar

y se

al is

pus

hed

alon

g th

e sh

aft o

r sl

eeve

to c

ompe

nsat

e fo

rw

ear.

Rem

edia

l Act

ion

s

x

It is

com

mon

to h

ardf

ace

the

slee

ve in

the

seco

ndar

y se

al a

rea

to m

inim

ize

the

dam

age

from

fret

ting

corr

osio

n.

x

Use

a n

on-p

ushe

r se

al, f

or e

xam

ple,

a m

etal

bello

ws

seal

, to

avoi

d th

e fr

ettin

g co

ntac

t.

x

If cr

evic

e co

rros

ion

is s

uspe

cted

, the

n an

yac

tion

to a

void

the

crev

ice

or p

rovi

de a

corr

osio

n-re

sist

ant s

urfa

ce tr

eatm

ent w

illco

rrec

t thi

s ef

fect

.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-39

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

Com

mon

Sea

l Fai

lure

Mod

es –

Sea

l Har

dwar

e

C1:

Phy

sica

l dam

age

A w

ide

varie

ty o

f sym

ptom

s fr

om c

hips

, min

ordi

stor

tion,

nic

ks in

met

al b

ello

ws,

to th

e ex

ampl

ein

the

pict

ure.

In th

at s

peci

fic c

ase,

car

e w

asta

ken

not t

o da

mag

e th

e fa

ces

by p

laci

ng th

ese

al o

n its

edg

e. U

nfor

tuna

tely

, it w

as n

otw

edge

d, a

nd it

rol

led

away

and

was

run

ove

r by

a fo

rklif

t tru

ck.

Cau

se

Not

obs

ervi

ng g

ood

fittin

g pr

actic

e:

x

Insu

ffici

ent c

lean

lines

s.

x

Exc

essi

ve fo

rce.

x

Use

of i

ncor

rect

tool

s, a

nd s

o on

.

Aft

er b

eing

car

eful

with

the

seal

face

s an

dse

cond

ary

seal

s, th

e ha

rdw

are

is s

omet

imes

dam

aged

by

acci

dent

.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-40

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C2:

Har

dwar

e ru

bbin

gC

erta

in c

ondi

tions

mig

ht c

ause

abn

orm

al w

ear

whe

re li

ttle

shou

ld o

ccur

, for

exa

mpl

e, th

e ou

ter

skin

of

the

rota

ry u

nit,

the

shaf

t (fo

r ex

ampl

e,ag

ains

t the

sta

tiona

ry s

eat)

, the

nec

k bu

sh, a

ndth

e th

rottl

e bu

sh in

the

back

of t

he s

eal p

late

.

In s

ever

e ca

ses,

the

part

mig

ht b

e he

ated

tosu

ch a

n ex

tent

that

it r

each

es it

s m

eltin

g po

int.

Cau

se

Pos

sibi

litie

s in

clud

e:

x

Bea

ring

failu

re.

x

Pum

p/m

otor

sha

ft m

isal

ignm

ent.

x

Sea

l cha

mbe

r to

o sm

all f

or r

otar

y un

it.

x

Uns

pigo

tted

stat

iona

ry u

nit s

lips

and

touc

hes

shaf

t.

x

Non

-pilo

ted

seal

pla

te to

uche

s sh

aft.

x

Set

scr

ews

in th

e ro

tary

uni

t com

e lo

ose

and

cont

act t

he s

eal c

ham

ber

wal

l.

x

Pie

ces

of th

e fa

ce b

reak

off

and

jam

bet

wee

nth

e ro

tary

uni

t and

the

seal

cha

mbe

r w

all.

x

Flu

sh c

onne

ctio

n lin

es e

xten

d to

o fa

r int

o th

ese

al c

ham

ber

and

touc

h th

e se

al.

x

Sin

gle-

sprin

g se

als

mig

ht r

ub th

e se

alch

ambe

r w

all i

f bro

ken

or o

ver-

com

pres

sed,

or a

re s

ubje

cted

to h

igh

spee

d.

x

Mul

tiple

spr

ings

bre

ak u

p an

d ja

m b

etw

een

the

rota

ry u

nit a

nd th

e se

al c

ham

ber

wal

l.

x

Pro

duct

or

othe

r se

al d

epos

its (

see

C10

belo

w)

mig

ht s

cale

up

on th

e se

al o

r on

the

seal

cha

mbe

r w

all.

x

The

rmal

exp

ansi

on c

ausi

ng th

e m

etal

bod

yor

oth

er p

art t

o ex

pand

and

, hen

ce, c

onta

ctth

e se

al c

ham

ber

wal

l.

x

Equ

ipm

ent v

ibra

tion.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-41

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C3:

Ero

sion

or

abra

sive

wea

rC

ircul

ar m

arks

on

the

outs

ide

diam

eter

of t

hero

tatin

g se

al b

ody

– of

ten

in li

ne w

ith a

circ

ulat

ion

inle

t.

On

stat

iona

ry s

eal h

ardw

are,

gro

ovin

g da

mag

eoc

curs

aga

in, o

ften

in li

ne w

ith a

circ

ulat

ion

inle

t.

Cau

se

Thi

s ca

n be

cau

sed

by H

ardw

are

rubb

ing

(C2)

.

It al

so c

an r

esul

t fro

m th

e in

com

ing

flush

cont

aini

ng a

bras

ives

and

ero

ding

the

seal

bod

y,es

peci

ally

if th

e flu

sh p

ress

ure

diffe

rent

ial i

s to

ohi

gh.

Als

o ca

used

by

wea

r de

bris

circ

ulat

ing

in th

ese

at c

ham

ber.

Rem

edia

l Act

ion

Sol

utio

ns c

an in

volv

e:

x

Cha

ngin

g th

e ci

rcul

atio

n in

let p

ositi

on.

x

Mak

ing

it ta

ngen

tial.

x

Che

ckin

g th

is in

let f

or p

rotr

usio

n in

to th

e se

alch

ambe

r.

x

Flu

shin

g w

ith a

cle

aner

flui

d.

x

Sel

ectin

g a

smal

ler

outs

ide

diam

eter

sea

l.

x

Bor

ing

out t

he s

eal c

ham

ber.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-42

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C4:

Driv

e fa

ilure

Thi

s ca

n oc

cur

with

bot

h th

e to

rsio

nal d

rive

devi

ces

of r

otat

ing

com

pone

nts

and

the

anti-

rota

tion

devi

ces

of s

tatio

nary

com

pone

nts.

Typ

ical

exa

mpl

es in

clud

e:

x

Wea

r/fra

ctur

e of

driv

e pi

ns.

x

Wea

r of

driv

e lu

gs.

x

Fat

igue

failu

re o

f met

al b

ello

ws

(an

adeq

uate

pro

duct

tem

pera

ture

mar

gin,

'T

,is

vita

l as

this

is o

ften

caus

ed b

yva

poriz

atio

n).

x

(4)

Fai

lure

of d

rive

scre

ws/

colla

rs, f

orex

ampl

e, s

et s

crew

s cu

tting

into

the

body

.

Cau

se

Pos

sibi

litie

s in

clud

e:

x

Jam

med

sea

l ass

embl

y.

x

Exc

essi

ve s

haft

end

play

.

x

Fai

lure

of a

xial

hol

ding

dev

ice.

x

Poo

r se

al fa

ce lu

bric

atio

n.

x

Exc

essi

ve s

eal f

luid

pre

ssur

e.

x

Sea

l fac

e ou

t of s

quar

e w

ith s

haft

axi

s.

x

Exc

essi

ve s

haft

run-

out.

x

Exc

essi

ve s

haft

defle

ctio

n.

x

Equ

ipm

ent v

ibra

tion.

x

Stic

k-sl

ip fa

ce fr

ictio

n gi

ving

sea

l fac

evi

brat

ion.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-43

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C5:

Spr

ing

dist

ortio

n an

d br

eaka

geA

ll m

echa

nica

l sea

ls r

equi

re m

ovem

ent t

o ke

epth

e fa

ces

toge

ther

dur

ing

chan

ging

pum

p an

dse

al c

ondi

tions

and

to c

ompe

nsat

e fo

r w

ear.

Spr

ing

actio

n is

obt

aine

d by

a s

ingl

e co

il sp

ring,

mul

tiple

coi

l spr

ings

, a m

etal

bel

low

s as

sem

bly,

or a

wav

e sp

ring

was

her.

Typ

ical

failu

re c

hara

cter

istic

s ar

e ra

dial

cra

ckin

gof

the

sprin

g se

ctio

n, e

spec

ially

on

the

insi

dedi

amet

er, s

trai

ght f

ract

ure,

wea

r m

arks

in e

nds

of s

prin

g co

ils a

nd o

n th

e sl

eeve

and

rot

ary

neck

s, a

nd b

uild

-up

of s

olid

con

tam

inan

tsar

ound

spr

ing(

s), m

akin

g th

em in

effe

ctiv

e.

See

als

o E

xces

sive

Tor

que

(B3)

, re:

bel

low

sas

sem

bly

failu

re.

Cau

se

The

se s

prin

g de

vice

s fa

il in

a v

arie

ty o

f way

s, f

orex

ampl

e, c

orro

sion

, str

ess-

corr

osio

n an

d fa

tigue

.

Ch

ecks

On

man

y si

ngle

-spr

ing

seal

s, th

e dr

ive

isun

idire

ctio

nal a

nd th

e sp

ring

shou

ld a

lway

s gr

ipits

mat

ing

part

s. W

ith s

uch

seal

s, r

ever

sero

tatio

n or

inco

rrec

t spr

ing

fittin

g ca

uses

the

sprin

g to

tend

to u

ncoi

l, sl

ip, d

isto

rt, c

rack

, or

even

bre

ak.

The

abo

ve a

nd o

ther

spr

ing

prob

lem

s ar

e m

ost

com

mon

on

high

vis

cosi

ty d

utie

s pr

one

toS

ludg

ing

(A26

) or

Bon

ding

(A

27).

On

mul

ti-sp

ring

seal

s, a

bui

ld-u

p of

sol

ids

arou

ndth

e sp

rings

can

mak

e so

me

sprin

gs in

effe

ctiv

ean

d, h

ence

, cau

se o

verlo

ad a

nd fa

ilure

of t

heot

hers

.

Rem

edia

l Act

ion

s

On

mul

ti-sp

ring

seal

s, d

iver

sion

of p

art o

f the

prod

uct c

ircul

atio

n th

roug

h th

e sp

ring

pock

ets

can

redu

ce fu

ture

bui

ld-u

p of

sol

ids.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-44

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C6:

Sea

l han

g-up

Thi

s oc

curs

whe

n th

e sl

idin

g as

sem

bly

ispr

even

ted

from

follo

win

g up

(by

mov

ing

axia

lly),

thus

leav

ing

a ga

p be

twee

n th

e se

alin

g rin

g an

dth

e se

at.

The

slid

ing

asse

mbl

y m

ovem

ent i

s ty

pica

llypr

even

ted

by a

bui

ld-u

p of

dep

osite

d di

ssol

ved

solid

s, c

orro

sion

, oxi

datio

n, o

r de

com

posi

tion

prod

ucts

. Thi

s po

ssib

ility

is p

rese

nt w

hene

ver

apu

sher

type

sea

l (w

here

the

seco

ndar

y se

al is

push

ed a

long

the

shaf

t or

slee

ve to

com

pens

ate

for

wea

r) is

use

d. S

ee C

okin

g (A

20)

and

Cry

stal

lizat

ion

(A25

).

Rem

edia

l Act

ion

s

x

Use

of

a no

n-pu

sher

type

sea

l, fo

r ex

ampl

e,m

etal

bel

low

s ty

pe.

x

Pro

visi

on o

f a s

uita

ble

quen

ch, f

or e

xam

ple:

•W

ater

to p

reve

nt d

epos

ition

of a

queo

usdi

ssol

ved

solid

s.

•N

itrog

en to

pre

vent

the

form

atio

n of

oxid

atio

n pr

oduc

ts.

•O

il or

sim

ilar

to p

reve

nt th

e fo

rmat

ion

ofco

rros

ion

prod

ucts

.

•A

sui

tabl

e co

olan

t que

nch

to p

reve

ntth

erm

al d

ecom

posi

tion

prod

ucts

from

form

ing.

x

Use

of

a se

al d

esig

n in

whi

ch th

e se

cond

ary

seal

s ad

vanc

e on

to c

lean

sur

face

s ca

n al

sohe

lp.

x

In m

any

case

s, m

echa

nica

l sle

eve

dam

age

that

has

occ

urre

d w

ill r

equi

re r

ectif

icat

ion

(incl

udin

g ha

rd fa

cing

in th

e se

cond

ary

seal

area

).

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-45

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C7:

Sle

eve

mar

king

and

dam

age

Thi

s m

ight

wel

l rel

ate

to S

eal H

ang-

Up

(C6)

,C

okin

g (A

20),

or

Cry

stal

lizat

ion

(A25

). T

hem

arki

ng o

n a

slee

ve (

or s

haft

if no

sle

eve

isfit

ted)

ofte

n gi

ves

a us

eful

indi

catio

n of

the

caus

e of

sea

l fai

lure

.

Thi

s m

arki

ng c

an b

e di

vide

d in

to th

ree

type

s:

x

Fro

m m

echa

nica

l rea

sons

– c

ause

s in

this

sect

ion

give

det

ails

.

x

Fro

m fr

ettin

g co

rros

ion

or c

revi

ce c

orro

sion

betw

een

the

slee

ve a

nd th

e se

cond

ary

seal

.S

ee C

orro

sion

at S

econ

dary

Sea

l Int

erfa

ces

(B7)

.

x

Ove

rall

corr

osio

n, u

sual

ly fo

und

on th

epr

oduc

t sid

e of

the

slee

ve; u

nles

s th

e se

al is

leak

ing

badl

y, th

e at

mos

pher

ic s

ide

is o

ften

in g

ood

cond

ition

. See

Cor

rosi

on o

f Sea

lH

ardw

are

(C9)

.

Mec

hani

cal c

ause

s ty

pica

lly g

ive

leak

age

only

whe

n ru

nnin

g an

d of

ten

leak

age

disa

ppea

rsw

hen

the

mac

hine

is s

tatic

.

Whe

n in

ope

ratio

n, a

n in

crea

se in

sha

ftec

cent

ricity

will

incr

ease

hyd

rody

nam

ic a

ctio

n,re

sulti

ng in

thic

ker f

luid

film

and

incr

ease

dle

akag

e.

Cau

se

Typ

ical

cau

ses

of s

leev

e m

arki

ng:

x

Con

tact

bet

wee

n O

-rin

g la

ndin

gs o

n th

ein

side

of

a ro

tary

sea

l rin

g is

oft

en c

ause

d by

an e

ccen

tric

or

mis

alig

ned

shaf

t. If

land

ing

wea

r is

sev

ere,

O-r

ing

extr

usio

n ca

n re

sult.

x

If ab

ove

cont

act o

ccup

ies

all t

he s

leev

eci

rcum

fere

nce,

it is

pro

babl

y ca

used

by

am

isal

igne

d se

al th

at fo

rces

the

seal

ing

ring

toos

cilla

te r

elat

ive

to th

e sh

aft s

leev

e on

ce p

erre

volu

tion.

Thi

s is

oft

en a

ccom

pani

ed b

yw

ear

on th

e in

side

dia

met

er o

f the

sec

onda

ryse

al o

n th

e se

alin

g rin

g.

x

If ab

ove

cont

act o

ccup

ies

part

of t

he s

leev

eci

rcum

fere

nce,

this

usu

ally

sug

gest

s an

ecce

ntric

or

gyra

ting

shaf

t. It

is o

ften

an

indi

catio

n th

at e

xter

nal f

orce

s ar

e im

posi

ngm

isal

ignm

ent b

etw

een

the

seal

face

s an

dca

usin

g le

akag

e.

x

A b

ent s

haft

ofte

n gi

ves

rise

to tw

o m

arks

diam

etric

ally

opp

osite

: one

on

the

fron

tla

ndin

g an

d on

e on

the

oppo

site

rea

rla

ndin

g. T

his

bend

ing

mig

ht b

e fr

om a

n ou

t-of

-bal

ance

sha

ft/ro

tor

asse

mbl

y.

x

Sev

ere

vibr

atio

n ca

n ca

use

the

O-r

ing

land

ings

to c

onta

ct, r

esul

ting

in fr

ettin

g an

dm

arki

ng in

to w

hich

fore

ign

mat

ter

can

lodg

e,th

us c

ausi

ng S

eal H

ang-

Up

(C6)

.

x

Fai

led

bear

ings

can

res

ult i

n ei

ther

incr

ease

dvi

brat

ion

or m

isal

ignm

ent.

x

Inco

rrec

t sle

eve

man

ufac

ture

or

seal

asse

mbl

y.

x

Lack

of

hard

faci

ng g

ives

exc

essi

ve w

ear

inse

cond

ary

seal

are

a of

sha

ft, e

spec

ially

ifab

rasi

ves

are

pres

ent i

n th

e pr

oduc

t.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-46

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C8:

Ove

rhea

ted

met

al c

ompo

nent

sW

hen

stee

l is

heat

ed, a

col

or c

hang

e ta

kes

plac

e. T

his

heat

ing

caus

es te

mpe

ring

and,

henc

e, lo

ss o

f re

quire

d m

echa

nica

l pro

pert

ies.

Thi

s co

lor

chan

ge m

ight

be

pres

ent g

ener

ally

or

rela

ted

to s

peci

fic c

ompo

nent

s.

Typ

ical

col

ors

and

tem

pera

ture

s th

at c

reat

eth

ese

colo

rs o

n st

ainl

ess

stee

l:

Str

aw Y

ello

w70

0-80

0°F

(370

-430

°C)

Bro

wn

900-

1000

°F(4

80-5

40°C

)

Blu

e11

00°F

(59

0°C

)

Bla

ck12

00°F

(65

0°C

)

Cau

se

An

easi

ly d

istin

guis

habl

e si

gn o

f sea

l tro

uble

.

Unl

ess

caus

ed b

y H

ardw

are

Rub

bing

(C

2), t

here

are

usua

lly o

ther

com

pone

nts,

that

is, s

eal f

aces

or s

econ

dary

sea

ls th

at a

re a

lso

dam

aged

and

assi

st d

iagn

osis

of

the

likel

y ca

use

of e

xces

sive

heat

. Typ

ical

rea

sons

are

dry

run

ning

,va

poriz

atio

n, e

xces

sive

hea

t soa

k, a

nd s

o on

.

Ch

ecks

Com

para

tive

anal

ysis

of p

arts

from

all

loca

tions

will

rev

eal w

heth

er th

e th

erm

al c

ondi

tion

was

loca

l to

one

com

pone

nt o

r an

ove

rall

exce

ssiv

ete

mpe

ratu

re.

C9:

Cor

rosi

on o

f sea

l har

dwar

eC

orro

sive

atta

ck r

esul

ts in

ove

rall

and

loca

l los

sof

met

al. D

amag

e ch

arac

teris

tics

are

usua

llyin

dica

tive

of th

e co

rros

ion

mec

hani

sm; t

hese

mec

hani

sms

are

as c

onve

ntio

nally

exp

erie

nced

in o

ther

eng

inee

ring

com

pone

nts.

Cor

rosi

on d

amag

e is

ofte

n no

t pre

sent

on

the

atm

osph

eric

sid

e of

the

seal

(un

less

it is

leak

ing

badl

y). S

eals

can

con

tinue

to fu

nctio

nad

equa

tely

unt

il qu

ite a

dvan

ced

stag

es o

fco

rros

ion.

Cau

se

Thi

s oc

curs

thro

ugh

the

vario

us u

sual

mec

hani

sms:

ove

rall

corr

osio

n, s

tres

s-co

rros

ion,

elec

trol

ytic

atta

ck, h

ydro

gen

embr

ittle

men

t,cr

evic

e co

rros

ion

and

fret

ting

corr

osio

n.

Ch

ecks

x

Che

ck m

ater

ial s

elec

tion

agai

nst t

he p

rodu

ctan

d its

con

ditio

ns.

x

Che

ck fo

r co

rrec

t pro

cess

ing

in m

anuf

actu

rew

ith s

eal s

uppl

ier.

x

Rev

iew

use

of

any

diss

imila

r met

als

(ele

ctro

lytic

act

ion)

.

Rem

edia

l Act

ion

s

x

A c

hang

e of

mat

eria

l.

x

Gro

und

the

pum

p ef

fect

ivel

y to

ear

th if

pitt

ing

from

ele

ctro

lysi

s is

sus

pect

ed.

EP

RI

Lic

ense

d M

ater

ial

Trou

bles

hoot

ing

to I

dent

ify C

ause

of S

eal F

ailu

re

7-47

Sym

pto

mC

har

acte

rist

ics

Cau

ses/

Ch

ecks

/Rem

edie

s

C10

:E

xces

sive

dep

osits

Dep

osits

fro

m th

e pr

oduc

t, co

rros

ion,

etc

., bu

ildup

on

the

rota

ry b

ody.

Thi

s ca

n ca

use

the

rota

ting

unit

to fr

eeze

in th

e se

al c

ham

ber.

Oth

er c

once

rns,

for

exam

ple,

Sea

l Han

g-U

p(C

6), m

ight

wel

l occ

ur fi

rst.

Cau

se

Inad

equa

te s

eal c

ham

ber

circ

ulat

ion

to fl

ush

out

the

depo

sits

and

sto

p th

em fr

om b

uild

ing

up.

Rem

edia

l Act

ion

s

In s

ever

e ca

ses,

a s

epar

ate

clea

n pu

rge

mig

htbe

req

uire

d.


8-1

8 MAINTENANCE

8.1 Introduction

Seal maintenance programs at most power plants fall within one or more of the followingcategories: reactive maintenance, preventative maintenance, and predictive maintenance basedon condition monitoring. The most cost effective maintenance program should be based onpredicted seal performance and its expected life. The least cost effective maintenance program isone based on reactions to failure. Reaction type programs result in unexpected plant shutdownsand reduced plant availability.

Except for seals in safety-related and critical applications, most maintenance is performed underthe reactive category because of a lack of control of the various factors that lead to prematureseal failure and the effort required to perform condition monitoring on such a large population ofseals. To prevent reactive maintenance of seals in critical applications, most plants implementsome level of preventative or periodic maintenance programs based on experience andmanufacturer recommendations. In safety-related installations, seals are maintained periodically,regardless of the condition of the seal to prevent unexpected plant shutdowns.

Maintenance in most power plants is performed by maintenance personnel at the plant withassistance from the plant engineer and seal manufacturer on unique problems and specializedprocesses. In all cases, plant maintenance personnel are responsible for seal removal andinstallation. However, to maximize their effectiveness, plant engineers and maintenancepersonnel should not be limited to removal and installation. They should be trained in the properdiagnosis of seal failure and how to correctly address the root cause of a seal failure. It, therefore,becomes particularly important to provide the proper level of training necessary to identify theproblem rather than to just maintain the seal. Appendix C lists organizations that provide trainingclasses, short courses, and seminars on the design, selection, operation, maintenance,troubleshooting, and failure diagnosis of mechanical face seals.

Key O&M Cost Point

The most cost-effective maintenance program should be based on predictedseal performance and its expected life. The least cost-effective maintenanceprogram is one based on reactions to failure. An effective preventative orperiodic maintenance program, based on plant experience and manufacturerrecommendations, should be implemented to improve plant reliability andprevent unplanned shutdowns.


Maintenance

8-2

8.2 Installation and Operation

As discussed in Sections 4 and 5, mechanical face seals are relatively precise and complexassemblies that are subject to a variety of failure modes. For reliable operation, mechanical sealsrequire the correct working environment, which demands good engineering, maintenance, andoperations practices, and well-written and detailed procedures. Written procedures should bekept current so that, as new information is acquired, it is properly accounted for andimplemented into working practice.

The following discussion outlines methods that can be utilized by plant engineers andmaintenance personnel to improve the chances of obtaining longer life from the seals. The topicscovered address:

x Seal handling and inspection

x Pre-installation equipment checks

x Seal installation

x Startup and operation


Personnel training is a very important aspect of a mechanical sealmaintenance program that is striving to achieve improvements in plantreliability. Comprehensive training courses covering mechanical seal designoptions, installation, operation, maintenance, troubleshooting, and failurediagnosis are regularly offered by seal manufacturers, universities, andresearch associates (see Appendix C).

8.2.1 Seal Handling and Inspection

This section covers pre-installation checks applicable to the mechanical seal itself and includesseal storage. Checks to be performed on the equipment are discussed in Section 8.2.2. Thesechecks should supplement rather than supercede manufacturer recommendations. These checksshould be tempered by plant personnel experience.

8.2.1.1 Packaging


Proper storage and handling of seal components is important to seallongevity and performance. Manufacturer’s recommendations should befollowed at all times.


Maintenance

8-3

Seal assemblies and spare parts are typically wrapped and boxed. If the package is opened with aknife for inspection, care should be taken to ensure that the faces and elastomeric seals are notcut or scored. If not used, seals should be repackaged in the same manner and returned to theiroriginal box, if practical, to ensure that proper labeling and identification is maintained. If thebox is unusable, then the replacement box should have proper labeling.

8.2.1.2 Storage

To protect the seals from damage, storage of the seal assemblies and spare parts should be inaccordance with the seal manufacturer's recommendations. The storage area should be clean, dry,and adequately warm and ventilated.

8.2.1.3 Handling

Many mechanical seal faces are brittle and fragile and can easily break if dropped. The metalcomponents of a mechanical seal provide the proper restraints and alignment needed foroperation. Care should be taken that these components are not damaged.

Protect parts from damage wherever possible. Avoid placing a seal face down on any surface,unless it is protected by a clean cloth or similar material.

Some parts are prone to attack by common liquids. For example, ethylene propylene rubber isattacked by mineral oil and silicone rubber is attacked by silicone oil.

8.2.1.4 Physical Checks of Mechanical Seals

Obtain specific drawings from the manufacturer. The drawings provide assembly details and keydimensions for fitting and installation. When sufficient information is not available, contact themanufacturer for advice. Technical recommendations and technical information provided withthe mechanical seal should be transferred to maintenance procedures for future use. Care shouldbe taken to note any safety/toxicity/industrial hygiene issues.

8.2.1.5 Seal Rotating and Stationary Components

x Check for physical damage

x Ensure drive pins and/or spring pins are free to move in the pin holes or slots

x Check that set screws are free in the threads. Set screws should not be reused becausedamage to the drive end might have occurred in previous use.

x Check metal bellows for damage that might cause leakage or improper alignment of thefaces.

x Check secondary seals for nicks or cuts. If the seals need to be replaced, make certain that thereplacement seals are of the same type to ensure fluid and temperature compatibility.


Maintenance

8-4

8.2.1.6 Seal Faces

Visually check for nicks or scratches. Face imperfections of any kind can lead to leakage andpremature failure of the seal. Detailed inspection of the seal faces for flatness is discussed inSection 8.2.3.1, Seal Dimensional Checks.

8.2.1.7 Gaskets

Check thickness against the manufacturer's specifications. Incorrect gasket thickness can lead toincorrect seal length settings and improper face loading.

8.2.1.8 Spring

Check rotation of spring coil when a single coil is used. The spring coil rotation should be suchthat shaft rotation tends to tighten the coil. Springs are available in right-hand and left-hand coilrotation. Some springs can be used bi-directionally.

8.2.2 Pre-Installation Equipment Checks

Proper equipment function is critical to seal performance and it is recognized that seal life isadversely affected by equipment misalignment and vibration. The following checks can be easilyaccomplished using good engineering practices and simple measuring instruments. Limits ofacceptability on runout provided in this section are general in nature. The seal manufacturershould be contacted for limits applicable to their products.


Pre-installation checks are an important element in reliable sealperformance. Personnel should perform the steps outlined herein to preventunsatisfactory seal performance.

8.2.2.1 Shaft Straightness (Figure 8-1)

Shaft straightness is checked with the shaft removed from the equipment. It is mounted betweencenters to check for runout between the bearing and the shaft or shaft sleeve at the locationwhere the mechanical face seal is installed.

Typical runout limits:0.004 inches (0.1 mm) for speeds d 1,800 rpm0.002 inches (0.05 mm) for speeds > 1,800 rpm


Maintenance

8-5

Figure 8-1Shaft Straightness Check

8.2.2.2 Shaft Runout (Figure 8-2)

Shaft runout is checked with the shaft installed in the equipment. Runout is checked at thelocation where the mechanical face seal is located on the shaft or shaft sleeve, and isaccomplished by slowly rotating the shaft against a stationary dial indicator.

Figure 8-2Shaft Runout Measurement

8.2.2.3 Squareness of Stuffing Box (Figure 8-3)

Squareness of the stuffing box is checked to ensure that angular misalignment does not occurupon installation. Angular misalignment is checked with the equipment completely assembledexcept for the seals. The measurement is made by mounting a dial indicator on the shaft and thenslowly rotating the shaft and dial indicator to measure the runout of the face that controls theangular placement of mating ring.

Typical runout limits for wedges, O-rings, and metal bellows seals:0.003 inches (0.08 mm) for speeds d 1,800 rpm0.0015 inches (0.04 mm) for speeds > 1,800 rpm

Typical runout limits for elastomer and PTFE bellows seals:0.007 inches (0.18 mm) for speeds d 1,800 rpm0.0035 inches (0.09 mm) for speeds > 1,800 rpm


Maintenance

8-6

Figure 8-3Stuffing Box Squareness Measurement

8.2.2.4 Rotational Balance (Figure 8-4)

Rotational balance of the shaft should be checked with the impeller installed as well as othercomponents that normally rotate with the shaft. Excessive out-of-balance can cause prematureseal failure. The acceptable amount of out-of-balance is dependent upon the specific applicationbut, in general, the deflection caused by out-of-balance should not exceed the limits defined in8.2.2.1 and 8.2.2.3 when the shaft is turning at normal operating conditions.

Figure 8-4Shaft and Impeller Rotational Balance Check

8.2.2.5 Shaft Bearing Clearances (Figure 8-5)

Shaft-to-bearing clearance can allow both radial and axial movement of the shaft. These tests areperformed with the shaft installed in the equipment. Radial movement is checked by loading theshaft laterally with a light force so that the shaft does not bend. Axial movement is checked bypulling and pushing the shaft along its axis.

Radial movement should be limited to 0.003 inches (0.08 mm) for rolling element bearings. Forplain bearings, the movement should not exceed the maximum bearing clearance specified by themanufacturer.

Axial movement of the shaft should be limited to 0.003 inches (0.08 mm). If this limit isexceeded, then the face seal load generated by the springs should be checked to ensure that itremains within the manufacturer's recommendation for normal operating conditions. Abnormaloperating conditions and stop/start conditions that cause excessive axial movement can lead toreduced seal life.


Maintenance

8-7

Figure 8-5Radial and Axial Bearing Clearance Checks

8.2.2.6 Shaft/Sleeve Diameter and Surface Finish (Figure 8-6)

The shaft and shaft sleeve should be checked to ensure that the diameter at the seal locations(including secondary seals) is within the seal manufacturer's recommendations.

The surface finish under the seal (especially at the secondary seal position) should be free ofmachine marks, and should have a roughness of less than 25 micro-inches (600 Pm) for staticseals and less than 10 micro-inches (250 Pm) for dynamic O-rings and wedge rings.

For elastomeric/rubber bellows, the shaft/sleeve surface finish can have fine machined marks butthe surface roughness should be limited to 50 micro-inches (1200 Pm).

Figure 8-6Measurement of Critical Shaft and Sleeve Diameters

8.2.2.7 Sleeve Hardfacing (Figure 8-7)

Sleeves are sometimes hardfaced to prolong their useful life in abrasive service. However,hardfacing should be limited to secondary seal areas and should not extend to the location wherethe set screws lock the seal to the sleeve. If the set screw lands on the hardfaced surface, thescrew grip might be impaired and allow relative movement between the seal and sleeve.


Maintenance

8-8

Figure 8-7Sleeve Hardfacing to Prolong Life

8.2.2.8 Sharp Edges (Figure 8-8)

Sharp edges are not acceptable where a seal must pass with an interference fit. Sharp edges canoccur at shaft steps, keyways, splines, holes, and so on. Sharp edges can cut or nick a soft sealingmember and create a leak path. If possible, chamfer the leading edge of the shoulder to allow theseal to slide over it.

Figure 8-8Lead-In Chamfers to Prevent Secondary Seal Damage During Installation

8.2.3 Seal Installation Checks

This section provides some basic step to follow during seal installation and the manufacturershould be contacted for detailed information and recommendations. Some of these steps requiresome type of measurement. It is therefore important to obtain assembly drawings from themanufacturer.

8.2.3.1 Seal Dimensional Checks

The overall dimensions and critical interface dimensions should be checked against drawings toensure that the mechanical seal is correct to the drawing. Some check should be made to verifythat the seal is able to compress to the correct length. Caution should be taken when compressingmetal bellows seals because over-compression might result in yielding of the bellows. If thebellows yield, they will not generate the required load at the installed length.


Maintenance

8-9

Seal faces should be inspected by an optical flat to ensure that they meet the flatnessrequirements specified by the seal manufacturer. Appendix B describes the typical proceduresused to check the seal face flatness and typical examples of out-of-flat conditions.

8.2.3.2 Seal Cavity Dimensions (Figure 8-9)

Seal cavity dimensions should be checked to ensure that proper clearance and alignment will beachieved and to prevent seal damage during installation. Check the seal cavity inside diametersand depths. Visually check for damage of the cavity that might have occurred during previousoperation or during disassembly.

Figure 8-9Seal Cavity Dimensional Checks Prior to Installation

8.2.3.3 Compression Length Tolerance

Interrelated dimensions between the shaft and seal cavity should be checked to ensure propercompression loading of the seal faces. It is important to correctly account for the gasket thicknesswhen calculating the compression of the seal.

Do not use previous set screw indention in the shaft/sleeve as a reference point because there canbe significant difference in the stacked height of seals, particularly between differentmanufacturers. It is also important to install the seal so that the set screws do not align withprevious indentations that might guide the set screw away from the preferred installationposition.

8.2.3.4 Auxiliary Glands

Auxiliary glands should be checked to ensure that fittings do not protrude into the seal cavity andcome into contact or affect the performance of the seal. The glands should also be checked toverify that they are clear of obstructions that could prevent proper circulation of the barrier orflushing fluids.


Maintenance

8-10

8.2.4 Seal Removal

As discussed in the beginning of this section, seal maintenance programs often occur as areaction to a seal failure rather than as a planned activity. As a result, seal removals are done atan accelerated pace in order to bring the plant or process back into service. Under this type ofcondition, special emphasis should be made to ensure that safety and failure evidence aremaintained.

8.2.4.1 Safety

Because of their tolerance to a variety of fluids, mechanical face seals are often used in toxic orhazardous processes. To ensure safety of personnel during the removal and handling of the sealand the fluid in the seal cavity, training and written instructions should be provided to clearlyidentify the type of equipment needed and other safety devices to be utilized during disassembly,handling, and storage.


Equipment contents and conditions should be fully known beforedisassembly to preclude injury.

8.2.4.2 Failure Evidence

As identified in Section 7, the best guide to determining the cause of failure of a seal is often thecondition of the seal. It is, therefore, important to properly mark, photograph, and carefully storethe seal and other related components for later detailed examinations. It is also recommendedthat some of the seal cavity fluid be retained because it might also be used to determine the causeof failure.

8.2.4.3 Seal Re-use and Inspection

It is strongly recommended that mechanical face seals not be re-used unless they have beenreconditioned to the manufacturer's specifications. The mating faces of mechanical seals developa wear pattern after an extended period of use and it is almost impossible to reestablish the samerelationship after their alignment has been disturbed. Even checking for damage by separatingthe faces can upset their relationship. The faces should not be separated unless it is absolutelynecessary. Whenever possible, inspection of the seals should be limited to visual externalinspection only.

8.2.5 Startup

Mechanical face seals are precision pieces of equipment. If they are to provide good service, theymust be correctly commissioned and operated. The primary aim of a proper startup is to ensurethat the seal does not initially run dry.


Maintenance

8-11

Key O&M Cost Point

Adherence to manufacturer’s recommendations during start-up andoperation is vital to seal longevity and performance.

8.2.5.1 Avoid Dry Running

If barrier or flushing fluids are used, ensure that the seal cavity is properly filled and that thereare no leaks. If the fluids in the seal cavity are circulated externally, verify that the equipment isfunctioning properly and delivering the required flow.

Fluids with low vapor pressures should be properly pressurized to ensure that the fluid at thefaces does not vaporize when the faces heat up during normal running.

8.2.5.2 Filtration

Dirt and particulate can cause a seal to fail in a very short period of time. Ensure that the sealcavity is completely clean and that the recirculated fluid has been properly filtered. Wheninstalling mechanical seals in new piping systems, it might even be necessary to temporarilyreplace the mechanical face seal with conventional soft packing until the system has beenthoroughly flushed of construction and installation debris.

8.2.5.3 Venting the Stuffing Box

The stuffing box should be properly vented to ensure that the seal chamber is completely filled.Never start a mechanical face seal before venting the seal cavity of air and foreign fluids. Ideally,the installation should allow the seal cavity to be vented automatically during pump priming, but,in some installations, it might be possible to flood the pump suction without purging the airtrapped in the top portion of the seal cavity. Special attention should be paid to verticalinstallations where the mechanical face seal is in the uppermost portion of the pressure boundary.


Proper venting of seal chamber prior to placing into service is critical to sealperformance and longevity.


9-1

9 REFERENCES AND BIBLIOGRAPHY

1. B. S. Nau, “Hydrodynamic Lubrication in Face Seals.” Paper No. E5, 3rd InternationalConference on Fluid Sealing, BHRA, Cranfield, Bradford, UK (1967).

2. J. G. Pape, “Fundamental Research on a Radial Face Seal,” ASLE Transactions. Vol. 11,No. 4, (October 1968).

3. E. Mayer. Mechanical Seals, 3rd Edition. J. W. Arrowsmith Ltd., Bristol 1969.

4. H. H. Buchter. Industrial Sealing Technology. John Wiley & Sons, Inc., New York 1979.

5. Alan O. Lebeck. Principles and Design of Mechanical Face Seals. John Wiley & Sons, Inc.,New York 1991.

6. Handbook of Fluid Sealing, edited by Robert V. Brink, McGraw-Hill, Inc., New York 1993.

7. Mechanical Seal Practice for Improved Performance, edited by Summers-Smith, MechanicalEngineering Publications, Ltd., for The Institution of Mechanical Engineers, London 1988.

8. API Standard 682: Shaft Sealing Systems for Centrifugal and Rotary Pumps, 1st Edition,American Petroleum Institute, Washington, D.C. October 1994.

9. Robert L. Johnson and Karl Schoenherr. Seal Wear, Wear Control Handbook, pp. 727-754,American Society of Mechanical Engineers, 1980.

10. “Seals Flow Code Development – 93,” NASA Conference Publication 10136, Proceedingsof a workshop held at the NASA Lewis Research Center, Cleveland, OH (November 3-4,1993).

11. F. A. Conner and M. T. Thew, “Trends in Mechanical Seal Performance at Three ProcessPlants in the Oil Industry,” 14th International Conference on Fluid Sealing, Publication 9,BHR Group, Mechanical Engineering Publications Limited, London (1994).

12. D. H. Ahlberg and E. C. Fitch, “Leaking Seals: Causes and Cures,” ASME Paper 79-DE-E-7,1979.

13. O. von Bertele, “Why Do Seals Fail Unpredictably,” Paper L4, presented at the 10thInternational Conference on Fluid Sealing, Innsbruck, Austria (April 3-5, 1984).

14. F. K. Orcutt, “An Investigation of the Operation and Failure of Mechanical Face Seals,”presented at the 4th International Conference on Fluid Sealing held in conjunction with the1969 ASLE Annual Meeting, Philadelphia, PA (1969).


References and Bibliography

9-2

15. John C. Hudelson, “Dynamic Instability of Undamped Bellows Face Seals in CryogenicLiquid,” pp. 381-390, ASLE Transactions 9. (1966).

16. J. W. Abar, “Failures of Mechanical Face Seals,” pp. 437-449, Metals Handbook, AmericanSociety of Metals, 8th Ed., Vol. 10, (1975).

17. Anon. “Identifying Causes of Seal Leakage,” Crane Packing Company, Form No. S-2031(1979).

18. Donald L. Berg, “Dynamic Seal Maintenance–Stuffingbox Sealing Considerations,”presented at NMAC 6th Annual Conference and Technical Workshop, Orlando, FL(December 9-11, 1996).

19. Steven Lemberger, “Mechanical Seal Maintenance,” presented at the NMAC 6th AnnualMeeting and Workshop, Orlando, FL (December 9-11, 1996).

20. E. Mayer, “High Duty Mechanical Seals for Nuclear Power Stations,” Paper A5, presented atthe 5th International Conference on Fluid Sealing, Warwick, Coventry, UK, March 30-April2, 1971, BHRA Group, Mechanical Engineering Publications Limited, London (1971).

21. H. Laumer and D. Florjancic, “Mechanical Seals for High Pressures and HighCircumferential Speeds,” Paper A4, presented at the 5th International Conference on FluidSealing, Warwick, Coventry, UK, March 30-April 2, 1971, BHRA Group, MechanicalEngineering Publications Limited, London (1971).

22. W. Schopplein. “Mechanical Seals for Aqueous Media Subject to High Pressures,” Paper E3,presented at the 8th International Conference on Fluid Sealing, University of Durham, UK(September 11-13, 1978).

23. William V. Adams and Peter Lytwyn. “Retrofit of an Unspared Main Boiler Feed Pump toEnd Face Mechanical Seals,” Paper No. 86-JPGC-Pwr-52, presented at the joint ASME/IEEEPower Generation Conference, Portland, OR (October 19-23, 1986).

24. H-J. Franke, R. Lachmayer, and J. Mosowicz. “Long-Term Tests of Mechanical Seals forHot Water Application,” 14th International Conference on Fluid Sealing, Publication 9,BHRA Group, Mechanical Engineering Publications Limited, London (1994).

25. J. Nosowicz and A. Eiletz. “Operating Performance of Mechanical Seals for Boiler FeedPumps,” 15th International Conference on Fluid Sealing, Publication 26, BHR Group,Mechanical Engineering Publications Limited, London (1997).

26. R. Metcalfe, N. E. Pothier, and B. H. Rod. “Diametral Tilt and Leakage of End Face Sealswith Convergent Sealing Gaps,” Paper A1, presented at the 8th International Conference onFluid Sealing, University of Durham, UK (September 11-13, 1978).

27. A. H-C. Marr, R. L. Phelps, and B. Katz. “Loss of Component Cooling Water Capability of aPWR Reactor Coolant Pump,” Paper No. 80-C2/PVP-28, presented at the Century 2 PressureVessels & Piping Conference, San Francisco, CA (August 12-15, 1980).



9-3

28. Thomas R. Morton. “Seal Performance from the Manufacturers Viewpoint,” Paper No. 84-PVP-115, American Society of Mechanical Engineers, New York, NY, 1984.

29. M. S. Kalsi, T. Horst, H. L. Richter, and M. Hojati. “O-Ring Static Seal Performance atElevated Temperatures Simulating A Loss of Component Cooling Water Accident,” Paper87-PVP-5, American Society of Mechanical Engineers, presented at the Pressure Vessel &Piping Conference, San Diego, CA (July 1987).

30. David L. Cummings and Sherman W. Shaw. “Increased Reliability of Reactor Coolant PumpSeals through Retrofit of Proven Technology,” paper presented at the American NuclearSociety Topical Meeting, Myrtle Beach, SC (April 17-20, 1988).

31. Takuya Fujita, et al. “Development of Rotary Shaft Seals for Primary Coolant Pumps forNuclear Reactors,” Preprint No. 87-TC-3D-1, presented at the STLE/ASME TribologyConference, San Antonio, TX (October 5-8, 1987).

32. Joseph A. Marsi and Dr. S. Gopalakrishnan, “Full-Scale Station Blackout Test Conducted onAdvanced RCP Mechanical Seal,” Nuclear Plant Journal. P. 86 (September-October 1988).

33. Ray Metcalfe, “Canadians Solve Seal Problems,” Nuclear Engineering Internationa. p. 46 (July 1989).

34. T. E. Greene and G. B. Inch. “Evaluation of Shaft Seal Leakage under Station BlackoutConditions for the Reactor–Circulation pumps at Nine Mile Point, Unit One,” presented atFifth International Workshop on Main Coolant Pumps, Orlando, FL (April 21-24, 1992).

35. Main Coolant Pump Seal Maintenance Guide. Prepared by Quadrex Energy Services forNuclear Maintenance Application Center: 1993. TR-100855.

36. A. Parmar. “Thermal Distortion Control in Mechanical Seals,” 12th International Conferenceon Fluid Sealing, BHRA, Cranfield, Bedford, UK (1989).

37. Antonio Artiles, Wilbur Shapiro, and Henry F. Jones. “Design Analysis of Rayleigh-StepFloating-Ring Seals,” Preprint No. 83-LC-38-2, presented at the ASLE/ASME LubricationConference, Hartford, CT (October 18-20, 1983).

38. L. A. Young and A. O. Lebeck, “The Design and Testing of Moving-Wave Mechanical FaceSeals Under Variable Operating Conditions in Water,” Preprint No. 85-TC-1C-1, presentedat the ASLE/ASME Tribology Conference, Atlanta, GA (October 8-10, 1985).

39. J. G. Evans. “New Developments in Bellow Seals for Improved Performance andReliability,” 14th International Conference on Fluid Sealing, Publication 9, BHR Group,Mechanical Engineering Publications Limited, London (1994).

40. R. Metcalf, T. A. Graham, and W. C. Wong. “Eccentric Seals for Nuclear Pumps,” 14thInternational Conference on Fluid Sealing, Publication 9, BHR Group, MechanicalEngineering Publications Limited, London (1994).



9-4

41. B. Tournerie, J. Huitric, D. Bonneau, and J. Prene. “Optimization and PerformancePrediction of Grooved Face Seals for Gases and Liquids,” 14th International Conference onFluid Sealing, Publication 9, BHR Group, Mechanical Engineering Publications Limited,London (1994).

42. N. W. Wallace and H. K. Muller. “The Development of Low Friction, Low LeakageMechanical Seals Using Laser Technology,” 11th International Pump Users Symposium &Short Courses, Houston, TX (March 7-10, 1994).

43. H. K. Muller, C. Schefzik, N. Wallace, and J. Evans. “Laserface Sealing Technology:Analysis and Application,” 15th International Conference on Fluid Sealing, Publication 26,BHR Group, Mechanical Engineering Publications Limited, London (1997).

44. I. Etsion, G. Halperin, and Y. Greenberg. “Increasing Mechanical Seals Life with Laser-Textured Seal Faces,” 15th International Conference on Fluid Sealing, Publication 26, BHRGroup, Mechanical Engineering Publications Limited, London (1997).

45. B. Antoszewski and J. Rokicki. “Tribology Aspect of the Laser Treatment for MechanicalSeals,” 15th International Conference on Fluid Sealing, Publication 26, BHR Group,Mechanical Engineering Publications Limited, London (1997).

46. Izhak Etsion. Improving Tribological Performance of Mechanical Seals by Laser SurfaceTexturing, Surface Technologies Ltd., Nesher, Israel, product catalog, 2000.

47. H. K. Muller. “Polymer Seal Rings in Sliding Contact with Silicon Carbide in a MechanicalSeal,” 15th International Conference on Fluid Sealing, Publication 26, BHR Group,Mechanical Engineering Publications Limited, London (1997).

48. N. D. Barnes, R. K. Flitney, and B. S. Nau, “Designing Chambers for Mechanical Seals,”World Pumps. (April 1990).

49. A. I. Golubiev and V. V. Gordeev. “Investigation of Wear in Mechanical Seals in LiquidsContaining Abrasive Particles,” Paper B3, 7th International Conference on Fluid Sealing,held at University of Nottingham, England (September 24-26, 1975).

50. David Nolan, “Sorting Out Slurry Pump Seals,” Coal. pp. 86-90 (1988).

51. James S. Budrow, “Seals for Abrasive Slurries,” Chemical Engineering. (September 1,1986).

52. M. S. Kalsi. “Development of a New High Pressure Rotary Seal for Abrasive Environments,”Proceedings of BHRA 12th International Conference on Fluid Sealing, Paper H2 (May1989).

53. M. S. Kalsi, W. T. Conroy, L. L. Dietle, and J. D. Gobeli. “A Novel High-Pressure RotaryShaft Seal Facilitates Innovations in Drilling and Production Equipment,” SPE/ IADC 37627,paper presented at SPE/IADC Drilling Conference, Amsterdam, The Netherlands (March1997).



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54. M. S. Kalsi. “A Novel High Pressure (up to 5000 psi / 340 Bars) Polymeric Rotary ShaftSeal,” World Tribology Congress, Organized by the Tribology Group of the Institution ofMechanical Engineers, London (September 8-12, 1997).

55. K. C. Wilson, G. R. Addie, A. Sellgren, and R. Clift. Slurry Transport Using CentrifugalPumps, 2nd Edition. Blackie Academic & Professional, London 1996.

56. R. K. Flitney and B. S. Nau. “Performance Testing of Mechanical Seals,” Fluid Sealing.Kluwer Academic Publishers, pp. 441-466.

57. Denis Buchdahl, Roger Martin, and Jean-Michel Girault. “Mechanical Seals QualificationProcedure of the Main Pumps of Nuclear Power Plants in France,” Fluid Sealing. KluwerAcademic Publishers, pp. 429-439 (1992).

NRC Information Notices and Generic Communications

58. USNRC Information Notice 95-42: Commission Decision on the Resolution of Generic Issue23, Reactor Coolant Pump Seal Failure, September 22, 1995.

59. USNRC Information Notice 87-51: Failure of Low Pressure Safety Injection Pump Due toSeal Problems, October 13, 1987.

60. USNRC Information Notice 96-58: RCP Seal Replacement with Pump on Backseat, October30, 1996.

61. USNRC GI–23: Reactor Coolant Pump Seal Failures and its Possible Effect on StationBlackout (Generic Letter 91-07).

62. USNRC Information Notice 93-61: Excessive Reactor Coolant Leakage Following a SealFailure in a Reactor Coolant Pump or Reactor Recirculation Pump, August 9, 1993.

63. USNRC Information Notice 93-84: Determination of Westinghouse Reactor Coolant PumpSeal Failure, October 20, 1993.

64. USNRC Regulatory Issue Summary 2000-02: Closure of Generic Safety Issue 23, ReactorCoolant Pump Seal Failure, February 15, 2000.

65. USNRC Draft Regulatory Guide DG-1008: Reactor Coolant Pump Seals, April 1991.


A-1

A MECHANICAL SEALS APPLICATION ANDMAINTENANCE GUIDE SURVEY

This appendix contains the form used to conduct the survey of fossil and nuclear power utilitiesto determine the most common failure modes, the root causes, and installation and maintenancerecommendations in support of the development of this guide.


Mechanical Seals Application and Maintenance Guide Survey

A-2

EPRI/NMAC Nuclear Maintenance Application Center

Mechanical Seals Application and Maintenance Guide

Survey

At the direction of the NMAC Steering Committee, NMAC has begun the preparation of an Applicationand Maintenance Guide for Mechanical Seals used in nuclear power plants. This survey is intended toobtain the most common problems with mechanical seals in use today. Information obtained from thissurvey will be used in developing a comprehensive and state-of-the-art Guide for the application, use,maintenance, repair, and troubleshooting of problems with mechanical seal. Your participation in thissurvey is vital to the accuracy and usefulness of this Guide. The Guide is intended to be a single sourcefor utility engineers and maintenance personnel to minimize problems with mechanical seals whileextending the number of cycles between seal inspections.

In order to evaluate the responses and to make comparisons between utilities to determine successful andunsuccessful practices, besides the responses to the following questions (which can be done by e-mail onthis form), the following information is also requested:

1) A copy of your latest procedures for mechanical seal maintenance, repairs, and troubleshooting.

2) Itemization of each individual pump's mechanical seal history since 1/1/90 (Maintenance Rule data isacceptable). This should include any mechanical seal failures and the root cause determination ofthose failures, corrective actions taken, and the seal inspection reports, even if the maintenance wassolely of a routine nature. Please include any mechanical seal leakage trending data available. Pleasecontact us if there is a question about this request.

3) Special problems that the plant may have experienced, and the plant's approach to addressing them.The outcome of each repair or corrective action will be a valuable addition to your response.

An important element of a typical NMAC Guide is to involve industry personnel in the review/ commentstages of guide development. Would someone at your facility be willing to participate as a member of ourTechnical Advisory Group (TAG) which typically involves review/comment of an initial draft and finalversion of the planned maintenance guide? Yes No

Please mail, fax or e-mail responses to: Mike Pugh1300 W. T. Harris Blvd.

Charlotte, NC 28262Fax: 704-547-6035

E-mail: [email protected]: 704-547-6004



A-3

Page 1 of 7EPRI/NMAC MECHANICAL SEALS MAINTENANCE GUIDE

SURVEY QUESTIONS

Contact Name: Phone: (_____)

Utility: Fax: (_____)

Plant: E-Mail:

1) Date of initial plant startup:

2) Number of loops: 1 2 3 4

3) Plant design: PWR BWR or Fossil

4a) Estimated number of all rotary shaft seals in your plant.

4b) Estimated number of mechanical seals in critical applications.

4c) Estimated number of mechanical seals in other applications.

5) Where mechanical face seals are not being used, select the two most important factors for notusing them (select two)

Cost Leakage

Unpredictable catastrophic failure potential Availability

Specialized training & maintenance Other (explain)

Types of Mechanical Seals, Manufacturers, and Applications in Power Stations

6) Manufacturers (check all that apply):

6a) Main Coolant Pump Seal:

(1) Westinghouse (3) BWIP

(2) Sulzer Bingham (4) AECL

6b) Other Mechanical Seal Manufacturers (check all that apply):

(1) Crane (4) Chesterton (7) Borg-Warner/BWIP

(2) Durametallic (5) Sealol (8) AST

(3) Burgmann Seals (6) Flexibox (9) Latty International

(10) Other

6c) Most common at your plant (select 3 numbers from list in Question 6b) .



A-4

Page 2 of 77a) Most common mechanical seal configurations in your plant (2 selections):

(1) Inside mounted with rotating seal head (pressure on outside diameter of face)

(2) Outside mounted with rotating, externally mounted seal head (pressure on inside diameterof face)

(3) Outside mounted with stationary, internally mounted seal head (pressure on insidediameter of face)

(4) Inside mounted with stationary, externally mounted seal head (pressure on outsidediameter of faces)

(5) Cartridge(6) Other (Specify)

7b) Which configurations have the most problems (select 2 from Question 7a) .

8a) Sealed Fluid (select all that apply)Incompressible Compressible

(1) Clean Water (6) Air/Nitrogen

(2) Service Water (7) Steam(3) Oil (8) Other (Specify) (4) Hydrocarbon

(5) Slurry(6) Other (Specify)

8b) Most common at this location (select 2 numbers from each category in Question 8a)

9) Most common secondary seals (select 2)

Elastomeric O-Ring Elastomeric ChevronElastomeric U-Cup Elastomeric Wedge

Metal Bellows Elastomeric BellowsOther (specify)

10) Select the 3 most common face material combinations from the list below

Rotating StationaryFace Face

Combination 1

Combination 2 Combination 3 (1) Carbon - Graphite (10) Aluminum - Bronze(2) Carbon - Babbit (11) Bronze(3) Ceramic (12) Monel(4) Nickel - Resist (13) Tungsten Carbide(5) Silicon Carbide (14) Phosphor - Bronze(6) Laminated Plastic (15) Carbon-Filled Teflon (nonoxidizing acids)(7) Teflon (16) Glass-Filled Teflon (oxidizing acids)(8) Stainless Steel (17) Hasteloy A, B, or C(9) Stellite Hard-Facing on (18) Other (specify)

Stainless Steel



A-5

Page 3 of 7

Present Failure Rates and Causes

11) Mean time between failure of mechanical seals resulting in leakage

less than 6 months 6 to 12 month 12 to 18 months

18 to 36 months 36 to 72 months Other (specify)

12) Symptoms of mechanical seal problems: Most Least NeverCommon Common Occurs

Visible or detectable leakage

Wear of rotating faceWear of counterfaceLoss of spring force due to contamination and

accumulation of solids

Loss of contact force due to spring element relaxationExcessive friction heat

Excessive friction torqueLoss of coolant/lubricantCorrosion

Other (explain)

13a) Causes of mechanical seal problems (select all that apply):

• Maintenance installation problem

(1) Improper seal face compression(2) Contamination or damage during installation

(3) Excessive eccentricity cause by set screw tightening sequence(4) Slippage due to incorrect set screw tip geometry (dog point versus cup point)(5) Slippage due to set screw material being too soft

(6) Elastomers not installed correctly(7) Elastomer/lubricant incompatibility

(8) Other

• Equipment interface/operation problem

(9) Mounting surface for seal not square/parallel to shaft(10) Excessive axial or radial movement (off Best Efficiency Point operation, cavitation, out

of balance, bent shaft, misalignment, bad bearings, etc.)

(11) Other

• Manufacturing problem

(12) Wrong or improper materials supplied

(13) Defects introduced during manufacturing(14) Other



A-6

Page 4 of 7• Application or system problem

(15) Incorrect seal selected for the application (e.g., vacuum applications should use adouble seal of some sort)

(16) Face materials improperly selected for the application(17) Improper environmental controls causing the seal to overheat or allow contaminants(18) Fluid vaporization across seal faces

(19) Pressure and/or temperature transients due to variable system operation(20) Equipment operating conditions not completely defined

(21) Material chemical attack and corrosion(22) Dirty or abrasive system(23) Product (e.g., crystallized boron) sticks to seal parts and keeps them from moving

properly

(24) Other

13b) Most common at your plant (select three from list in Question 13a)

Inspection and Predictive Maintenance Methods as Related to theMechanical Seal Condition

14) Frequency of mechanical seal visual inspection (check all that apply and provide number of sealsinspected in each category)

Monthly seals Quarterly seals

Annually seals Every outage sealsOver two years (specify period and number of seals) , seals

15) Predictive Maintenance Schedule is based on:

Manufacturer Recommendation

Plant/Utility ExperienceImportance of the Equipment to Plant Operation and Plant Output Power Level

Importance of the Equipment to Plant SafetyOther (specify)

16) Predictive Maintenance Methods Used (select all that apply)

Temperature measurementLeakage detection

Vibration levelNone

Other (specify)

Periodic Preventive Maintenance/Replacement Performed Regardlessof the Actual Condition of the Mechanical Seal

17a) Equipment under Periodic Preventive Maintenance (specify or provide list)

Safety-Related

Critical For Plant Output

Balance of the Plant

None



A-7

Page 5 of 7

17b) Maintenance/replacement frequency (if none in 17a, skip this question)

Every OutageEvery Other Outage

Other (specify)

Plant-Specific Approaches to AddressMechanical Seal Problems and Maintenance

18) Troubleshooting is performed by:

Plant MaintenanceManufacturer Representative

Outside Contractor

19) Mechanical seal repairs are performed by:

Plant Maintenance; the level of maintenance being:Install onlyChange O-rings/static seals

Change seal faces and finish machine, i.e., grind, lap, inspectRemanufacture complete assembly

Manufacturer RepresentativeOutside Contractor

20) Spare parts and inventory (check all applicable options)

Spare mechanical seals for high priority equipment are kept at the plant warehouseSpare parts for some key seals for high priority equipment are kept at the plant warehouse

Seals and spare parts are stocked by manufacturers and ordered as neededSpare parts are machined from material stock kept at the plant

None of the above (explain)

21) Please provide a copy of your data sheet used to specify mechanical seals (if available).

Data sheet attached

22) Shaft stiffness criterion used to determine the suitability of a mechanical seal for a givenapplication.

Shaft deflection at seal L3/D4 ratio Specify value: Other None

23) List 3 applications in which mechanical seal problems continue to be difficult to solve.

Application 1:

Application 2:

Application 3:

Provide details of the 3 applications in the following table:



A-8

Page 6 of 7

ApplicationData Requested

1 2 3

Application: safety-related/critical/ balance of theplant

Equipment type (pump, agitator, compressor...)

Equipment manufacturer

Mechanical seal manufacturer(Model No or type if available)

Estimated leak rate at failure

Fluid (clear water, service water, slurry, ...)

Temperature, • F

Pressure, psi

Speed, rpm

Approximate shaft diameter

Face material

- Stationary

- Rotating

Seal design

- Balanced or unbalanced

- Single, double, or tandem

- Secondary seals (bellows, elastomers,...)

- Face loading achieved by single coil, multiple,& Belleville springs; bellows, elastomers, ...

- Flushing: Process fluid, external source,...

Mean time between failures

Parameters monitored for predictive maintenance(leakage, temp, pressure, vibration,...)

Root cause of failure determined (Yes/No)

Provide or attach the root cause

Frequency of periodic maintenance if any

Attach description of alternative solutions(successful or pursued)



A-9

Page 7 of 7

Training Provided for In-House Maintenance Personnel

24) Mechanical seal training is provided to

Equipment engineer

All in-house rotating equipment maintenance personnel

Only selected group of maintenance personnel

No training is provided

25) If training is provided what is the frequency of re-training

Every year Every 3 years

Every 5 years or more Other

26) Does your plant require contractors to have formal mechanical seal training before commencingrepair or replacement work?

Yes

No


B-1

B INSPECTION OF SEAL FACES FOR FLATNESS

B.1 Optical Principle

Lapped surfaces of seal parts are inspected for flatness using an optical flat and monochromaticlight. Light is passed through the optical flat, then reflected off the lapped surface, and backthrough the optical flat. When a gap exists between the optical flat and lapped surface, the lightreflections off the lapped surface and the optical flat interfere with each other, preventing someof the light from passing back through the optical flat. Between the dark bands, the reflectionsreinforce each other and produce light bands. This phenomenon produces a series of dark andlight bands when the optical flat is viewed from above, as shown in Figure B-1. The parallel darkbands form where the change in distance between the flat and lapped surface is one-half thewave length of the light as shown in this figure.

An optical flat is made from transparent material, normally quartz or Pyrex, which is very flat.Different size optical flats with different flatness tolerances are available. Typically, seal partsare inspected with an optical flat that is flat within 2 to 5 micro-inches (one micro-inch or 1 P in.is one-millionth (0.000001) of an inch). Optical flats can be flat within the specified tolerance onone or both sides. Single-sided flats are normally adequate for seal inspection. Coating on the flatincreases its reflectivity and makes the light bands easier to see.

A monochromatic light source emits light of a known wavelength. The most common type is ahelium-filled tube that emits orange/yellow light with a wavelength of 23.2 P in. The light bandsvisible through the optical flat are one-half the total wavelength. Consequently, each band(consisting of one light and one dark band) that is visible represents a gap of 11.6 P in. Theactual width of the bands cannot be related to the flatness of the part. The total number of bandsseen during inspection is a function of the gap that is created between the flat and the lappedsurface, not the flatness. Manufacturers will specify flatness in light bands, normally withoutregard to the size of the part. A seal part that is required to be flat within 2 light bands has aflatness tolerance of 23.2 P in. over the specified surface.


Inspection of Seal Faces for Flatness

B-2

Figure B-1Using an Optical Flat to Determine Seal Face Flatness Light Bands

B.2 Procedure for Measuring Face Flatness

When measuring the flatness of seal parts, the following basic good practices should be used toobtain accurate results.

x The optical flat and lapped surface should be free of dirt or other particles. Parts can bewiped with a lint-free cloth or brushed off with a fine bristle brush prior to setting the flat onthe lapped surface.

x Avoid putting any unnecessary force on the parts being inspected. The tolerances for lappedsurfaces are extraordinarily small and exerting unnecessary force on the parts can distort theflatness.

x The size of the flat needs to be matched to the part. Do not use an optical flat that is muchlarger and heavier than what is required.



B-3

x When inspecting carbon seal parts, place the carbon seal ring on a flat surface, such asanother flat or a lapped surface, like a carbide seal ring.

x Perform the inspections in a controlled environment. Changes in temperature and humiditycan affect flatness readings.

x Flatness measurements should only be taken when the part being inspected and the flat areboth at a uniform room temperature. For example, if the flat is at room temperature and thepart has just been brought in from an uncontrolled cold environment, the warm flat mightdistort a cold surface.

x View the optical flat from the correct angle. The flatness reading can be seriously distortedby determining the flatness when viewing the part with too great of incidence angle. Lightbands should be determined when looking straight down on the part, as shown in FigureB-2, at a viewing angle of close to 90q. If the flatness reading is taken with a viewing angleof 60q, each light band represents 13.4 P in. instead of 11.6 P in.

Figure B-2The Viewing Angle Typically Should be 80qq to 90qq While Checking Flatness Using aMonochromatic Light Source

A procedure for measuring flatness on seal rings and other toroidally shaped lapped seal surfacesis provided below. This method places an air wedge under one side of the flat to help determineif the part is convex or concave, or if it has other out-of-flatness conditions.

1. Place the lapped part under the monochromatic light. If the part is a carbon ring, make sure itis adequately supported.

2. Clean the lapped surface and the optical flat of dust with a lint-free cloth or fine bristle brush.

3. Place the flat on the lapped surface.



B-4

4. Use a piece of lint-free tissue to create an air wedge. Place the tissue between the left side ofthe lapped surface and the optical flat. Slowly pull the tissue out until the edge of the tissue isat the edge of the lapped surface. The tissue can be manipulated until a light band patternwidth that is easy to view is visible. If the tissue wedge is too thick or foreign particles arebetween the flat and the lapped surface, the light band pattern will be too narrow to read. Tocheck to see if the air wedge is too thick, use light thumb pressure at the air wedge to varythe appearance of the light bands.

5. The light bands are used to determine the degree of flatness. When interference bands arestraight, parallel, and equally spaced, the surface is assumed to be flat to within 11.6 P in.

6. Interpretation is carried out noting the number of bands intersected by a straight tangent line,as in the examples shown in Figures B-3 through B-7. Out-of-flatness is measured bymultiplying this number by 11.6 P in. It is important to note that, if the bands are inconsistentor missing, it is necessary to draw two imaginary centerlines 90q apart and perpendicular tothe axis of the part, and then draw line AB at 45q, connecting the two previous lines (seeexamples in Figures B-6 and B-7).

The procedure used by different seal manufacturers to determine flatness might vary from theprocedure above. The relationship to successful performance and flatness measurements shouldbe kept in perspective. If the lapping and measurement techniques provide consistent successfuloperation, the procedures should not be changed.

Figure B-3Flat Within One Light Band (The distance x is dependent on the amount of air between theoptical flat and the face and does not indicate lack of flatness.)



B-5

Figure B-4Bands Bend on One side and Line AB Intersects 3 Bands (The face is therefore out-of-flatby 3 light bands or 35 PP in.)

Figure B-5This Indicates an Egg-Shaped Curvature of 2.5 Light Bands (That is, 29 PP in. Line ABintersects 2 bands and falls between another 2 at the center of the ring. Line A'B'intersects 2 bands that curve in the opposite direction.)



B-6

Figure B-6Bands Show a Saddle Shape Out-of-Flat Condition of 3 Light Bands,35 PP in.

Figure B-7Bands Show a Cylindrical-Shaped Part with a 3-Light Band Reading Error

Figure B-8Band Symmetrical Pattern Indicates a Conical Convex or Concave Part. (The out-of-flatness is measured by the number of bands on the part, that is, 3 bandsor 35 PP in.)


C-1

C TRAINING COURSES

The following is a listing and description of training materials or courses that are presentlyknown to NMAC that are available for enhancing skills involved with mechanical seals. Theyare broken down into two major categories. The first category of training, Category A, supportsa basic understanding of mechanical seal installation and maintenance practices as well aspersonnel qualification materials. The second category, Category B, provides a higher level oftraining that will improve craftsmanship and understanding of seal operation and technology, andalso gives a greater insight into performance, problem analysis, and plant implications. NMAChas reviewed these course offerings in limited detail. Reference herein is not intended to be anendorsement of the materials but simply a reference, should additional training information bedesired by the membership.

CATEGORY A

EPRI Maintenance Performance Evaluation Test Bank

The Maintenance Proficiency Evaluation Test Bank (MPETB) is a database of validated andreliable task-specific written and performance tests developed by participating utilities followingthe proven MPE methodology referenced in EPRI technical reports. The database, madeavailable exclusively to utility participants in this project, already contains a large population oftask-specific written and performance tests that can be administered to plant or contractorpersonnel. Currently there are several tests for mechanical seals that are available toparticipating members. If you would like to find out more about the Mechanical Seals MPEsyou can visit the EPRI webpage at http://www.epriweb.com/epriweb2.5/ecd/np/mpe/index.htmlor contact Loran Maier at 704-547-6152.

Annual International Pump Users Symposium and Short Courses ProgramTexas A&M Turbomachinery Laboratory

College Station, Texas 77843-3254Phone: 979/845-7417Website: http://turbolab.tamu.eduContact: Dr. Bailey, Marketing Director

Background:The Turbomachinery Laboratory receives inquiries from fluid handling and rotating equipmentusers who are looking for intensive training opportunities in addition to those currently offered attheir symposia. In response to these inquiries, they have initiated a cooperative effort with someexhibiting companies to provide information on their professional development opportunities.These technical training sessions are listed below, by company, with a brief description of eachcourse.


Training Courses

C-2

FLOWSERVE Educational Services GroupPump Training Programs taught at the Learning Resource Center in DallasWebsite: www.flowserve.com

Course Title: Take the Mystery Out of Pumps and Mechanical SealsAudience: Engineers, supervisors, and craftsmen specializing in Pump and Mechanical SealReliability Improvement.

Synopsis: This five-day course, split equally between classroom and hands-on learning activities,will provide participants with a strong understanding of centrifugal pumps and mechanical seals.

ChestertonChesterton offers learning via the Internet to allow students to learn at their own pace on a moreflexible schedule. Students are provided with immediate feedback on their progress through eachcourse. An index of terms is provided under the Performance Support section. Students cansearch this section for terms pertinent to their topic area. Course outlines are available at theirwebsite: www.activedistancelearning.com/distancelearning/index.asp

Course Title: Mechanical Seal Principles IStudents will learn each aspect of mechanical seals, including the purpose of a mechanical seal,its component parts, their classifications, its materials of construction, proper operation,environmental controls, and troubleshooting for some basic mechanical packing failures.

CATEGORY B

Georgia Institute of TechnologyPaul Weber Space Science and Technology Building on the Georgia Tech CampusRegistration: 404/385-3501Contact: Greg Stenzoski, Marketing Dept.

Course Title: Fluid Sealing TechnologyThis four-day, annual course provides an extensive introduction to fluid sealing and is designedto meet the needs of equipment designers, plant and maintenance engineers, and technical salesengineers. This course has been presented at Georgia Tech for the last 11 years. It utilizes thefluid sealing and tribology expertise of both Georgia Tech and the BHR Group (BritishHydromechanics Research Group).

A sound understanding of the complex factors involved in successful fluid sealing is essential forengineers who specify, design, operate and maintain machinery and mechanical equipment. Sealsspecialists show how an understanding of basic engineering factors can be used to practicaladvantage. Fluid sealing technology is based on disciplines as diverse as lubrication, friction,wear, properties of materials, mechanical design, fluid mechanics, and heat transfer. All of thesefactors are considered in the discussion of different types of seals, seal materials, and sealingapplications.

Annual International Pump Users Symposium and Short Courses ProgramSee above discussion for background on the below listed courses.


Training Courses

C-3

FLOWSERVE Educational Services GroupPump Training Programs taught at the Learning Resource Center in Dallas, TX.Website: www.flowserve.com/

Course Title: Improving Pump, Mechanical Seal, and Systems Reliability ThroughMaintenanceAudience: Pump and mechanical seal craftsmen and technicians.

Synopsis: Designed to assist craftsmen in becoming more effective and efficient, and to addvalue to equipment operation and reliability through thorough maintenance. More than three fulldays of the five-day course are spent conducting hands-on learning activities.

Course Title: Improving Pump, Mechanical Seal, and Systems ReliabilityAudience: Maintenance engineers, supervisors, and others responsible for reliabilityimprovement will benefit from this course, as will their companies.

Synopsis: This weeklong program equips the attendees to identify the root cause of pumpfailures and apply appropriate corrections. Over 50 failures and 90 corrections are studiedutilizing real pumps and mechanical seals, both static and in operation in our six learning labs.

Chesterton

Chesterton Distance Learning Course Curriculum:Chesterton offers learning via the Internet to allow students to learn at their own pace on a moreflexible schedule. Students are provided with immediate feedback on their progress through eachcourse. An index of terms is provided under the Performance Support section. Students cansearch this section for terms pertinent to their topic area. Course outlines are available at:www.activedistancelearning.com/distancelearning/index.asp

Course Title: Mechanical Seal OperationMechanical seals are designed and engineered differently for specific reasons. Differentapplications require diverse mechanical seal designs and operational characteristics. This coursewill describe the different ways that mechanical seals can be designed to operate in order toperform their tasks.

Course Title: Common Mechanical Seal FailuresTo further increase mechanical seal life, we must be able to analyze premature failures. Many ofthese incidents have symptoms that can tell us what caused it. By examining these failuresclosely, we can try to eliminate their reoccurrence. This course will identify common mechanicalseal failure symptoms and their possible causes.

International Conference on Fluid SealingThis conference is held every two to three years and the first conference dates back to April1961.


Training Courses

C-4

BHR Group Ltd.The Fluid Engineering CentreCranfieldBedfordshire MK43 0AJ, UKContact: Mrs. Catherine Cox, The Conference OrganizerTel: 44 (0) 1234 750422Email: [email protected]

Description:This sealing technology forum is the premier event in its field and never fails to provideimportant and interesting information and new insights into old problems. The aim is to furtherimprove sealing reliability and effectiveness.


D-1

D LISTING OF KEY INFORMATION

The following list provides the location of key Pop Out information in this report.

Key O&M Cost Point

Emphasizes information that will reduce purchase, operating, ormaintenance costs.

Section Page Key Point

3.4 3-12 Seal cartridges are pre-assembled mechanical face seal assemblies thatcontain all of the essential components. Cartridges are used to packagemechanical face seals for ease of handling and installation. Eventhough material cost is higher, cartridges save money by simplifyingmaintenance and eliminating installation related failures.

6.1 6-1 Seal monitoring programs vary greatly from utility to utility, and fromsite to site due to different equipment designs, operating philosophies,and different rates of forced outages experienced. For many plants,condition-based monitoring is limited to visual observations with littleactual quantification except for main coolant pump mechanical faceseals.

6.3 6-5 Monitoring and data logging of key performance parameters can serveas very useful tools for trending wear and performance degradation ofmechanical seals and preventing unscheduled outages.

7 7-1 Seal performance is often directly linked to equipment performance andreliability. An in-depth inspection and review of seal failures canimprove equipment availability and performance.

8.1 8-1 The most cost-effective maintenance program should be based onpredicted seal performance and its expected life. The least cost-effectivemaintenance program is one based on reactions to failure. An effectivepreventative or periodic maintenance program, based on plantexperience and manufacturer recommendations, should be implementedto improve plant reliability and prevent unplanned shutdowns.

8.2.5 8-11 Adherence to manufacturer’s recommendations during start-up andoperation is vital to seal longevity and performance.


Listing of Key Information

D-2

Key Technical Point

Targets information that will lead to improved equipment reliability.


3.1 3-2 Mechanical face seals come in a variety of configurations, materials, anddesigns for primary sealing faces, secondary seals, springs, and drivemechanisms. Options also include unbalanced or balanced designs,whether the primary seal or the mating seal is rotating, and whether thefluid pressure is on the outside or the inside surface of the seal. Sealdesign for a given application should be selected after a carefulevaluation of trade-offs discussed in this section, Section 3.

3.3 3-11 Some applications require the use of multiple seals to provide forflushing or barrier fluids, or pressure staging to deal with higherpressures. Flushing is used to remove contaminants, to cool the faces,or to provide for proper lubrication. Selections include back-to-back,face-to-face double arrangements, and a choice of buffer fluid or barrierfluid, depending upon application.

3.5 3-16 Mechanical seals are often installed in the same cavity that is designedto accept conventional packings. This limits the fluid circulation aroundthe seal, leading to high seal temperatures and accumulation of solids.An enlarged seal chamber with tapered bore can dramatically improvefluid circulation, lowering seal temperature and eliminatingaccumulation of solids.

3.6.1 3-20 Mechanical face seals can be unbalanced, fully balanced, or partiallybalanced to reduce the face loading due to hydraulic pressure. The termbalanced refers to the case where the average pressure load on the faceis less than the sealed pressure. Most mechanical face seals have abalance ratio of between 0.65 to 0.85. This range provides reduced faceloading without potential concern of face parting.

3.6.2 3-21 Pressure distribution across the seal face width can be linear, concave,or convex and it can change with variations in pressure, temperature,and seal wear. This can affect seal performance (leakage, torque,temperature) during operation.

3.8 3-24 For satisfactory performance, the seal design and material selectionsshould satisfy the PV limit and the ''T limit under all operatingconditions to ensure that fluid film is maintained between the seal faces.Loss of film can lead to immediate seizure and seal failure.

3.9 3-28 Seal designs with special features to enhance lubrication at the sealinginterface (for example, hydrodynamic grooves, recesses, or laser-textured surfaces) can extend the pressure, speed, and temperaturelimits. The trade-off (for example, higher leakage rate versus increasedreliability under transient conditions) should be carefully evaluatedduring seal selection.



D-3

3.10 3-28 The hydrostatic seal design is a non-contacting mechanical face sealthat permits some controlled flow rate to pass between the faces. Toprevent dry running, the seal requires that some pressure be applied tothe tapered side prior to rotation.

4.2 4-2 The eventual failure mode of all mechanical face seals is leakage that isconsidered unacceptable for the seal design/configuration being used.Excessive leakage can cause unacceptable loss of fluid, reduction ofpressure, or contamination of the system fluid by the barrier fluid indouble-seal installations. Level of acceptable leakage is dependent uponthe application.

4.4.1 4-5 For satisfactory performance, the seal design and material selectionsshould satisfy the PV limit and the ''T limit under all operatingconditions to ensure that fluid film is maintained between the seal faces.Loss of film can lead to immediate seizure and seal failure.

4.4.3 4-6 Mechanical seals are often installed in the same cavity that is designedto accept conventional packings. This limits the fluid circulation aroundthe seal, leading to high seal temperatures and accumulation of solids.An enlarged seal chamber with tapered bore can dramatically improvefluid circulation, lowering seal temperature and eliminatingaccumulation of solids.

4.4.4 4-7 Thermal distortions of seal faces due to operational transients cancause positive coning (contact on ID) or negative coning (contact onOD) of the seal faces. Coning in excess of film thickness can cause filmrupture seizure or face parting, resulting in a large increase in leakage.

4.4.4 4-8 Pressure distribution across the seal faces is affected by seal faceconing due to changes in pressure and speed as well as the wear-inprocess. Excessive coning causes seal failure either due to seizure orface parting. Hard face versus soft face material combinations are moretolerant of coning than if both faces are hard.

4.4.5 4-10 Operation away from Best Efficiency Point (BEP) is a frequent cause ofshort seal life/seal failures. Off BEP conditions cause large shaftdeflections and vibrations resulting in premature degradation ofmechanical seals.

4.4.6 4-13 Static and dynamic misalignment between seal faces can cause strongfluid pumping action across the faces causing either inward pumping oroutward pumping of the product fluid and/or buffer fluid. Leakagesunder misaligned conditions can be several times the normal leak rate.

4.4.6 4-13 Premature wear of the primary sealing faces and secondary seals,causing excessive leakage when stationary and when running, are alsocommon symptoms of excessive misalignment.

4.4.7 4-15 Mechanical face seals are precision components, requiring the sealingfaces to be flat, typically within one light band (11.6 x 10-6 inches) acrossone-inch width. Too much out-of-flatness can lead to excessive sealleakage.



D-4

4.4.8 4-16 Conventional mechanical face seals rely on a small amount of wavinessautomatically created by face distortions due to mechanical loads tofunction properly. Too perfectly flat seal faces on structurally robustseal rings prevent the faces from distorting and developing a fluid film.This results in seal failure due to seizure. Fortunately, this is a rareoccurrence.

5.2 5-3 Seal selection requires a detailed and systematic evaluation of all of thesignificant application parameters, for example, fluid type, pressure,temperature, speed, normal operating conditions versus designconditions, radiation exposure and maintenance. Appropriate datasheets and check lists should be used to ensure a thorough andcomplete evaluation of suitable alternatives and trade-offs. Prototypequalification tests should be performed for all critical applications.



D-5


Denotes information that requires personnel action or consideration inorder to prevent injury or damage, or ease completion of the task.


7.2.2 7-7 The importance of maintaining As Found conditions is important tofailure mode determinations. Personnel should be instructed toexercise care during the disassembly steps.

7.3 7-12 Visual examination is an important element in determining failuremechanisms. Personnel should be attentive during disassembly tobe alert for evidence of incipient or chronic failure mechanisms.

8.2 8-2 Personnel training is a very important aspect of a mechanical sealmaintenance program that is striving to achieve improvements inplant reliability. Comprehensive training courses coveringmechanical seal design options, installation, operation,maintenance, troubleshooting, and failure diagnosis are regularlyoffered by seal manufacturers, universities, and researchassociates (see Appendix C).

8.2.1.1 8-2 Proper storage and handling of seal components is important toseal longevity and performance. Manufacturer’s recommendationsshould be followed at all times.

8.2.2 8-4 Pre-installation checks are an important element in reliable sealperformance. Personnel should perform the steps outlined hereinto prevent unsatisfactory seal performance.

8.2.4.1 8-10 Equipment contents and conditions should be fully known beforedisassembly to preclude injury.

8.2.5.3 8-11 Proper venting of seal chamber prior to placing into service iscritical to seal performance and longevity.

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