Corrosion Protection of Duplex Corrosion Protection of Duplex Stainless Steel at Elevated Stainless Steel at Elevated

Temperatures in an Offshore Temperatures in an Offshore Environment by Thermal Spray Environment by Thermal Spray

Application of Aluminum Application of Aluminum Coating SystemCoating System

A Twin Wire Arc Spray ApplicationSteve Lutereksluterek@hfwindustries.com

HFW INDUSTRIES, INC.196 Philadelphia St. /PO Box 8Buffalo, NY 14207PH.: 716-875-3380 / FAX: 716-875-3385

Craig Maguirecraig_j_maguire@dresser-rand.comDresser-Rand CompanyPO Box 560Olean, NYPH: 716-375-3351 / FAX: 716-375-3718

IntroductionIntroductionThe purpose of this presentation is to discuss the design and application of thermal spray aluminum (TSA) to reduce or eliminate stress corrosion cracking (SCC) of system components

A number of chloride stress corrosion cracking failures on offshore components were documented in the north sea during 2001 and 2002

Failures occurred in 316 stainless steel, as well as duplex stainless steel subjected to elevated temperatures of 150° C (302° F)

Location of EquipmentLocation of EquipmentThe equipment that requires corrosion protection is located topside on a floating production, storage and offloading (FPSO) vessel.

“Graphic Courtesy of Woodside Australia Energy”

Location of EquipmentLocation of EquipmentThe topside equipment includes gas turbine driven Dresser-Rand DATUM gas compressors, with associated gas seal panel piping and valves.

Photo of Aluminum Thermal Sprayed Pipes and Valves Courtesy of Dresser-Rand

Location of EquipmentLocation of EquipmentA second FPSO project has topside TSA requirements as well. The compressor cases and heads for this project are carbon steel.

Photo Courtesy of HFW Industries, Inc.” Petrobras compressor case being TSA coated”

Evaluating the ProblemEvaluating the Problem

Solve the stress corrosion-cracking problem Initial cost Method of application Projected life cycle cost Delivery cycle Historical data and documentation

The criteria used for evaluating the problem was:

Developing SolutionsDeveloping Solutions

A partial enclosure Schedule 160 piping in place of schedule 80, T316 stainless steelHastelloy or Inconel in place of T316 stainless steel for piping and valvesDuplex stainless steel in place of doubling the wall of T316 stainless steelPaint systems good to 538° C (1000° F)The thermal spray application of an aluminum coating system

Alternate methods were evaluated to protect the equipment:

Evaluating SolutionsEvaluating Solutions

Use of a partial enclosure would not completely protect the equipment Increasing the wall thickness of 316 stainless steel pipes would work for a short timeHastelloy and Inconel were found to be from 7 to 17 times more costly TSA (thermal spray aluminum) is a well documented solution, but not widely used in North America

Considerations:

Thermal Spray AluminumThermal Spray Aluminum

Aluminum thermal spray coatings, both sealed and unsealed, gave complete base metal protection from corrosion for 19 years on steel structures

Where aluminum thermal spray coatings have chipped or scraped, corrosion did not progress, suggesting the occurrence of galvanic protection

Documentation supporting TSA as the solution:

The American Welding Society completed a 19-year study of corrosion protection in 1974. The study concluded that:

Thermal Spray AluminumThermal Spray Aluminum

NORSOK standards developed for North Sea applications state that TSA for elimination of maintenance coatings as well as SCC protection should be one of several areas subject to special evaluation for this application.

Documentation supporting TSA as the solution:

Thermal Spray AluminumThermal Spray Aluminum

The US Army Corps of Engineers in their “thermal spray system selection” CEGS-09971 state that TSA is an excellent choice for high temperature 400° C (750° F) protection

Aluminum coatings between 3 mils (.003”) and 7 mils (.007”), offered complete protection of bare metal and are given a rating of 10 by ASTM D610 in sea water

Documentation supporting TSA as the solution:

Specifications for TSASpecifications for TSAThe coating process evaluated for this application is TWAS (twin wire arc spray), a thermal spray process

Specifications for TSASpecifications for TSA

• Defining the minimum job standards• Safety and operator training• Qualification of the coating system• A substrate properly cleaned, with an anchor tooth profile

developed for bonding• The thermal spray coating properly applied to a

predetermined minimum thickness• A sealer or topcoat

The TSA system in its simplest form consists of:

Qualification of TSAQualification of TSA

Five bond strength test specimens of a suitable substrate are TSA coated following thickness and flatness requirements

Epoxy one coated specimen together with an uncoated specimen

A tension testing machine with self aligning tooling is used to pull the specimens to failure

Dresser Rand’s Specification and ASTM C633 require :

Qualification of TSAQualification of TSA

Interpretation of results include determining the location and type of failure

The strength of the coating is then calculated

Reporting includes material description as well as details of results, interpretation and adhesion strength of the bonding agent

Dresser Rand’s Specification and ASTM C633 require :

TSA ProceduresTSA Procedures

Oil, grease, dirt and other foreign materials is removed from the surfaces to be coatedAll sharp edges, fillets, corners and welds need to be hand ground smooth

Part temperature a minimum of -12° C (10° F) above the dew pointRelative humidity less than 90%

Surface preparation for TSA requires the following:

TSA ProceduresTSA Procedures

Areas designated non-coated are masked and protected during blasting and coating

Air used for grit blast must be clean and dry

Surface preparation for TSA requires the following:

TSA ProceduresTSA Procedures

Grit blast using an aluminum oxide grit and a blasted surface profile of 150-250AA

The blasted surface will be “white metal blast”

If coating cannot be applied within a four (4) hour period, a reblast is required

Surface preparation for TSA requires the following:

TSA ProceduresTSA Procedures

Spray equipment should be calibrated

Spray parameters documented on the “wire spray process control card”

Typical gun distance for a twin wire arc spray of aluminum is 152 – 203 mm (6 – 8 inches)

The coating procedure requires:

ELECTRIC ARC SPRAY PARAMETER RECORD HFW JOB NO.: _________________

CUSTOMER: ___________________

ITEM: _________________________

BASE MATERIAL: _______________

COATING THICKNESS: __________

COATINGS

BOND COAT TOP COAT W IRE TYPE

CLEANING

GRIT SIZE

BLAST PRESSURE

BLAST DISTANCE

BLAST ANGLE

SPRAY

GUN TYPE

NOZZLE CAP

NOZZLE POSITIONER

VOLTS

AMPS

AIR PRESSURE

PRE HEAT

STANDOFF (INCHES)

FEED RATE

GUN DISTANCE

GUN ANGLE

NOTES: OPERATOR:______________ DATE:_________ R:/W INW ORD/ELECTRICARC SPRAY PARAMETER RECORD

TSA ProceduresTSA Procedures

The use of daily booth qualification, bend test

Coat a sample of suitable material 50mm X 100mm to 200mm X 1.3mm (2” X 4”to 8” X .050”)

Bend the sample around a 13 mm (1/2”) diameter mandrel, 180 degrees

The coating procedures require:

• If the coating exhibits minor cracking in the radius, and cannot be lifted with a knife blade, it passes

TSA ProceduresTSA Procedures

The surfaces to be coated, be preheated between 52° C (125° F) and 93° C (200° F)

Spray parameters should be monitored during coating

Masks should be developed for complex part geometry that introduce areas of overspray overlap

The coating procedure requires:

TSA ProceduresTSA Procedures

All thermal spray coatings have inherent porosity

The seal coat chosen for additional protection was Metcoseal SA

This sealer is rated for excellent corrosion resistance at temperatures ranging from 80° C (176° F) to 480° C (900° F)

Sealing the coating is also a component of the TSA system offering additional protection:

TSA Quality RequirementsTSA Quality Requirements

The coating shall be uniform in texture

The coating shall be free of visible evidence of discontinuities when subjected to 10X magnification visual examination

The coating thickness is to be measured at a minimum of 5 random sites every 9 square meters (81 square feet)

Acceptance criteria is stated as:

Permascope Inspection

TSA Certification RequirementsTSA Certification Requirements

Dresser Rand part number, purchase order number and coating specification number

Batch size and identification number

Name and address at which coating was applied

List of coating thickness measurements recorded for each component

Manufacturer’s certification for wire used

Certification is the last requirement and includes:

TSA AdvantagesTSA AdvantagesData is available supporting long predictable life

Compared with “high quality” paint schemes, today’s twin wire arc spray aluminum coatings can be cost competitive

TSA forms oxide layers which enhance protection

Offers cathodic protection as well as surface protection

TSA AdvantagesTSA Advantages

Excellent resistance to marine environments

Low life cycle cost, eliminate or reduce inspection and maintenance

Very competitive when compared to options of changing base materials

TSA DisadvantagesTSA DisadvantagesInitial cost can be higher than paint, when compared to low cost paint schemes, and old technology flame spray, thus leaving the impression that TSA is very expensive

Blast cleaning and application procedures are more critical than paint

TSA equipment is more costly

Process qualification and operator training are very stringent

TSA SummaryTSA SummaryPainting is generally done with a team of painters mobilized once a year to take care of a planned annual inspection or a running maintenance list. In most cases this is done on structural items

This is minimized or eliminated with TSA

As more marginal oil fields with minimally manned or unmanned facilities are developed, anything that is relatively maintenance free for the life of the field will be worth investigating

TSA ConclusionTSA ConclusionThe aluminum coating, applied by the twin wire arc spray process, and the high temperature sealer used in this application, should provide years of corrosion protection based on documented case study, the AWS 19-year study and historical data

Longer life and lower life cycle cost than some paint systems

This coating system will act as surface protection against stress corrosion cracking on the duplex stainless steel

Acknowledgments Acknowledgments

Allan KiddDirector of Development EngineeringDresser-Rand

Edward Wilber Focus Factory ManagerDresser-Rand

Dave SeibMetallurgy SupervisorDresser-Rand

Joe MalmgrenSystem and Packaging engineerDresser-Rand

Russ MalinowskiProject Manager – Petrobras ProjectDresser-Rand

Philip M. McCabeProject EngineerDresser-Rand

Claus Wohlert-Jensen Rotating Equipment Specialist Fluor Amec Enfield Area Development Project

The authors would like to acknowledge the following people for their help and input:

References References Dresser-Rand FPSO’s(Floating Production Storage and Offtake facilities)Summary description of 6/28/2004

Woodside Web Page DataNational Development PlanWoodside Energy Ltd2003 and 2004

Norsok StandardM-001Rev. 3, Nov. 2002

Norsok StandardM-501Rev. 5, June 2004

United States Army Corp of Engineers

USACE EM 1110-3401

Chapter 5

Thermal Spray Coating Selection

January 1999

Sulzer Metco Description and Application Guide for Metco Sealers

Metcoseal SA

Silicone Aluminum

Physical properties, application procedures and typical applications

Thermal Spraying, Practice, Theory, and Application

American Welding Society

550 N.W. LeJune Road

Miami, FL 33135

Specification for the Application of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and their Alloys and Compositesfor the Protection of Steel

AWS C2.23M/C2.23:2003

NACE No. 12, SSPC-CS 23.00

An American National Standard

196 Philadelphia StreetBuffalo, New York 14207-0008

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web site: www.hfwindustries.com