Design Considerations for High Temperature SealingValve Manufacturer’s Association Conference, 2017

Nashville, TN

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Agenda

• Introduction

• Seal Service Conditions

• Design Considerations & Materials

• Basic Principles

• What makes a good seal?

• Metal-to-Metal Sealing Concept

• Leak rates

• Types of Metal Seals

• Conclusions & Best Practices

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Elastomer Seals

Metal Seals

Inflatable Seals

Graphite Seals PTFE/PEEK

Components & Seals

Assemblies

Mechanical Seals

High Performance Sealing Overview

Extreme Service Conditions for Seals

• High temperature / Cryogenic

• High pressure /Ultra high vacuum

• Cycling

• Chemical compatibility/Purity

• Radiation

• Longevity

• Ultra low leak rates /Fugitive emissions

• Low outgassing/Permeability

• Resiliency / Spring back

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Seal Type & Material: Design Considerations

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• Leak Rate

• Temperature & Pressure

• Chemical Compatibility

• Loading/Fasteners

• Manufacturability

• Elasticity / Spring back

• Abrasion Resistance

• Joining / Weldability

• Movement / Fatigue

• Economical

6 Disclaimer: Above are general working values only.

Materials

What Makes a “Good” Seal?

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Two Separate Properties:

• Elasticity

• Plasticity

In ONE MATERIAL

Example: Elastomer O-Ring

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Elasticity Plasticity

These 2 functions ensure and maintain specific pressure in service

Specific Pressure

Elasticity –vs- Plasticity: Separate Performance

Plastic Deformation & Surface Finish

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Elasticity

• Spring Force & Spring Back:

• Spring or

• Metal Substrate Profile

• Spring Rate Varies Based on:

• Seal Type

• Jacket/Coating.

Plasticity

• Jacket or Plating/Coating

Surface Finish

• Lathe Turned

Plastic Deformation Examples

Silver Plating: O-RingPoor Flange Finish: Radial Marks

Silver Jacket: Spring-EnergizedGood Flange Finish: Concentric Marks

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Plasticity: Jacket vs Plating

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Maximum Recommended Operating Temperatures for Platings & Coatings

Metal to Metal Sealing Concept

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No Metal to Metal Contact

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Compression Creep

• Seal not protected

• Bolt preload limited

• Creep allows loss of preload

• Increases with temperature

Metal to Metal Sealing: Groove

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Before Tightening After Tightening

• Seal is protected

• Bolt preload increased

• Creep minimized

Metal to Metal Sealing: Limiter

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HELICOFLEX® Type HN208a Shown

• Seal is protected

• Bolt preload increased

• Creep minimized

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High-temperature related issues Metal-to-metal Non metal-to-metal

Separation of function allows a load component

which can be designed accordingly

Load component, which typically is the seal itself,

can easily be overstressed

Mechanical strength of assembly

Only a matter of maintaining metal-to-metal contact

over operating life via appropriate joint design

anticipating reduced material strenght at high

temperature.

Assembly relaxation at high temperature has a direct

negative effect on seating stress hence on sealing

performance.

Sealing material creep over timeAppropriate seal design implies

self-compensated creep

Bolt load acting over the whole operating life

and all the way through the seal

dramatically increases creep.

Maintaining seating stress

(springback capacity)

Only a matter of maintaining metal-to-metal contact

over operating life via appropriate joint design

anticipating all events

Creep has to be compensated by joint assembly

elasticity (bolts, flanges) which strongly deteriorates

at high temperature

Differential expansion

(during transients)

Metal-to-metal joint concept is based on separation

of functions, hence allowing more flexibility in

adding specific features in joint and/or seal design.

Non metal-to-metal joint implies less design

flexibility. Only specific sealing material selection

will allow coping with differential expansion.

Significant adavantage

Significant disadavantage

Relative disadvantage

Initial load required for

yielding @ ambiant

Required seating load at ambiant can be very high

having selected a sealing material capable of high temperature

Metal to Metal Sealing: Summary

Leak Rate Illustration

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Gas Flow(Pa.m3/s) of He

Criteria Illustration Time Volume

10-13 Helium Pinhead 2200 Years 0,1 cm3

10-11 Helium Pinhead 20 Years 0,1 cm3

10-9 Helium Thimble 5 Years 1,5 cm3

10-7 Helium Thimble 2 Weeks 1,5 cm3

10-5 Bubble tight Magnum of Champagne 6 Months 1,5 dm3

10-3 Bubble tight Bucket 2 Weeks 15 dm3

10-1 Bubble tight Tanker truck 20 Weeks 12 000 dm3

10 Bubble tight Tanker truck 1 Day 12 000 dm3

ZERO LEAKAGE DOES NOT EXIST

Metal O-Rings

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• Sealing Concept

• Elastic deformation of high strength metal tubing

• Moderate load & spring back

• Plating or Coating added to improve leak rate

Metal C-Rings

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Internal pressure

External pressure

Axial pressure

• Sealing Concept

• Elastic deformation of a metal “C” substrate

• Reduced load

• Moderate spring back

• Pressure-energized by the system

• Soft plating or coating to improve leak rate

Metal E-Rings

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• Sealing Concept• Elastic

deformation of “bellows” like convolutions

• Low load

• High spring back:

90% to 100

• Pressure-energized by the system

• No plastic deformation

• Wear coatings

Jacketed Spring Energized Seals

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HELICOFLEX® Shown

• Sealing Concept

• Elastic deformation of helical spring

• Moderate to high load

• Moderate spring back

• Spring Rate tuned to application

• Plastic deformation of outer jacket to improve leak rate

• Flexibility in Profiles, Shapes & Materials

Controlled Density Graphite

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Valve Stem Packing

FlangeSealing

FARGRAF® Shown

ORIGRAF® Shown

Laminated Graphite Seal

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• Metal and graphite composite

• High precision and complex geometry

• Control of graphite flow

• Up to 15 MPa pressure

• Triple-offset valves

• LNG, Steam …

• Low leak rates

• High resistance over time

Spiral Wound Gasket

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Outer Limiter

Winding & Filler

Inner Limiter(Optional)

Cross Section

Limiter Rings• Carbon Steel• Stainless Steel• High Strength Alloy

Windings• Stainless• High Strength Alloy

Fillers• PTFE• Graphite• Mica• Ceramic

VITALFEX® Shown

Conclusions & Best Practices

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• Metal seals offer the widest range of design solutions for high temperature service

• Materials

• Seal Profiles

• Coatings / Platings

• Sealing must be considered early in the valve design

• Load: Fasteners, Flanges, Seats

• Finish: specific to material – geometry critical

• Seal design is specific to each application

AppendixCommonly Used Materials in Extreme Sealing Applications

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Metals: Elemental

27 Above values are reference only.

Metals: Stainless Steel

28 Above values are reference only.

Metals: Nickel Based Alloys

29 Above values are reference only.

Metals: Super Alloys

30 Above values are reference only.

Commonly Used Elastomers

31 Above values are reference only.

Flexible Graphite Grades Used

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Basic materials Materials with

inhibitor

PMUC

Material

N 998 I 980 NP 998 NS 200

Typical Applications High purity

material for

specific

application

Standard

grade for

industrial

application

Grade with active

corrosion inhibitor

EDF qualified

grade for nuclear

applications

Carbon content > 99,8 > 98 > 99,8 > 99,8

Ash content < 0,2 < 2 < 0,2 < 0,2

Inhibitor content 0 % 0 % 1 à 3 % 0 %

Chlorine content

(ppm)

30

50

30

Sulfur 200

Chlorine 30

Halogen 80

Temperature

resistance in

oxidizing atmosphere

500°C

932°F

450°C

842°F

450°C

842°F

500°C

932°F

Above values are reference only.

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