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NiDINickelDevelopmentInstitute

GUIDE TO THE SELECTION AND USE OF HIGHPERFORMANCE STAINLESS STEELS

Metallurgy - Properties - Corrosion Performance -Fabrication

A Nickel Development InstituteReference Book Series No. XX XXXX

Page 1 9/3/99

TABLE OF CONTENTS

INTRODUCTION ........................................ 3

CLASSIFICATION OF GRADES ........................................ 5

AUSTENITIC HIGH PERFORMANCE STAINLESS STEELS ...................................... 5FERRmC HIGH PERFORMANCE STAINLESS STEELS ................................................ 9DUPLEX HIGH PERFORMANCE STAINLESS STEELS ............................................... 10

PHYSICAL METALLURGY ............................................... 13PHASE RELATIONS IN THE IRON-CHROMIUM-NICKEL SYSTEM ............................................ 13SECONDARY PHASES ............................................... 17KINETICS OF PHASE PRECIPITATION REACTIONS ............................................... 21AUSTENITIC STAINLESS STEELS ............................................... 22FERRmC STAINLESS STEELS ............................................... 24DUPLEX STAINLESS STEELS ............................................... 26

MECHANICAL PROPERTIES ............................................... 28AUSTENmC STAINLESS STEELS ............................................... 29FERRITIC STAINLESS STEELS ............................................... 31DUPLEX STAINLESS STEELS ............................................... 33

PHYSICAL PROPERTIES ............................................... 34

CORROSION RESISTANCE ............................................... 36

RESISTANCE TO INORGANIC ACIDS .37RESISTANCE TO ORGANIC ACIDS .43RESISTANCE TO ALKALIES AND ALKALINE SALTS .46CHLORIDE- AND OTHER HALIDE-CONTAINING AQUEOUS ENVIRONMENTS .48NEAR NEUTRAL ENVIRONMENTS - NATURAL WATERS AND BRINES .53INFLUENCE OF MICROBIAL ACnVITY .57OXIDIZING HALIDE ENVIRONMENTS - CHLORINATED COOLING WATERS AND BLEACHSOLUTIONS .58ACIDIC ENVIRONMENTS CONTAINING HALIDES- FLUE GAS CONDENSATES .61

STRESS CORROSION CRACKING ............................ 65

WATER AND BRINE ENVIRONMENTS ................................ 66SOUR OIL AND GAS ENVIRONMENTS ................................ 70HYDROGEN ENVIRONMENTS ................................ 73

CORROSION ACCEPTANCE TESTS ............................ 74

FABRICATION ................................ 78HOT WORKING ................................ 79COLD WORKING ................................ 81ANNEALING ................................ 83

MACHINING ................................ 86

WELDING ................................ 87

AUSTENmC STAINLESS STEEL GRADES ................................ 89FERRITIC STAINLESS STEEL GRADES ................................ 92DUPLEX STAINLESS STEEL GRADES ................................ 93

SURFACE CONDITION ................................ 97

APPLICATIONS ............................................ 98

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Materials Workshop for Nuclear Power PlantsStainless Steel and Nickel-Base Alloys

Presented by

Mr. Curtis W. KovachDr. Nicole Paulus-Kinsman

of the

Nickel Development Institute (NiDI)

Workshop Schedule

8:15 am

8:30 am

9:30 am

Welcome and Introduction

Basics of Stainless Steel and Nickel-Base Alloys

Corrosion Basics

10:30 am

11:30 am

1:00 pm

Welding Stainless Steel

Lunch

High Strength Stainless Steels (Discussion)

2:00 pm

3:00 pm

3:45 pm

Advanced Stainless Steels

Microbiologically Influenced Corrosion

Conclusion

The format for this workshop is flexible and open. Questions may beasked at any time and examples from the floor can be discussedduring the session or one-on-one afterwards.

September 9, 1999

NIDI NUCLEAR POWER PLANT WORKSHOP

Conpany US Nuclear Regulatory Commission

Location: Rodville. Maryland Date: SeptLeSt9

High

ATTENDEE INFORMATION N0CE PerfromanceMailing List Stainless Steel

Book

Name: Phone:

Title:

Address:

Name: Phone:

Title:

Address:

Name: _ Phone

Title:

Address:

Name. Phone:

Title:

Address:

Name: Phone_

Title:

Address:

Name: Phone:

Title:

Address

--

RUJEDI Curtis KovachConsultantNICKEL DEVELOPMENT INSTITUTE

Head Office214 King Street West, Suite 5 10Toronto, ON Canada M5H 3S6Telephone 416-5917999Fax 416-591-7987

Technical Iarketing Resources, Inc.3209 McKnight East DrivePitsburgh, PA 15237-6423 U.S.A.Telephone 412-369-0377Fax 412-367-2353ckotuch8trnr-inc.cosn

I7~~I~bDI Dr. Nicole PaulusK, Po" D I ConsultantNICKEL DEVELOPMENT INSTITUTE

1Iead Office214 King Street West, Suite 510Toronto, ON Canada Mll 3S6Telephone 416-591-7999Fax 416-591.7987

Technical Marketing Resources, Inc.3209 McKnight East DrivePittsburgh, PA 15237.6423U.S.A.Telephone 412-369-0377Fax 412-367-2353npaulus6tmrinc.com

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NiDICASE STUDYNo 150021994

NUCLEAR SERVICE WATER PIPING

OSKARSHAMN NUCLEARPOWER PLANT,FIGEHOLV1, SWEDEN

Coastal nuclear power plants, which use brackish andoften polluted water in their service water systems, faceone of the most demanding service environments in theindustry. The Swedish utility OKG AKTIEBOLAG hasthis operating environment at their Oskarshamn NuclearPower Plant in Figeholm, Sweden. The brackish,polluted Baltic Sea water used in the service water systemcaused extensive corrosion of the original systemmaterials. Material replacement, testing, and evaluationhave been on-going since 1978 giving OKG some of themost extensive operating experience with 6 Mo austeniticstainless steels, titanium and other high performancereplacement materials of any nuclear power plant in theworld. This case study reviews the problems experiencedwith original system materials; replacement material eval-uation programs; and actual performance of the alloys inservice; therefore, providing valuable insight for utilitieswith equally severe operating environments.

THE SYSTEM

The Oskarshamn Nuclear Power Plant has three operatingunits. The start-up dates for these units and other basicoperating data for the service water system can be foundin Table 1. The units all have open emergency servicewater systems and have both closed and open once-through portions of their regular service water system.The condensers in all three units are fed by the openportion of the service water system.

Both the standard and emergency service water systempiping was originally rubber-lined carbon steel. The

Table ISystem Description

DESCRIPTION UNIT 1 UNIT 2 UNIT 3

Start Up 1972 1974 1985

System Testing 1970 1972 1983Power Output (MWc) 460 620 1.210

Regular System 700 1,000 1,700Flow Rate (kg/s)Emergency System 25 400 700Flow Rate (kg/s)Main Condenser 20,000 26.000 45,000Flow Rate (kg/s)

emergency service water system in all three plants is nor-mally only operated during shut-down periods. Aconstant low flow rate is maintained through the systemwhen it is not in operation to prevent water stagnation.The emergency systems in all three units were designedso that, even if the pumps stopped, the operating systemwould never be empty. The return pipes go to the highestpoint in the system.

The open sections of the service water systems use brack-ish, polluted water from the Baltic Sea. The water entersthe plant through culverts and is pumped through a shortsection of underground piping before entering the units.The closed portions of the service water system usedemineralized water. Units I and 2 have open, once-through service water systems in all but the reactorbuilding, which has a closed system. The majority of thepiping and over 100 heat exchangers in these units are inthe open portion of the service water system. These are theolder units with start-up dates in 1972 and 1974,respectively. Corrosion problems became evident in bothunits within two to three years after commencement ofcommercial operation. The first problems arose in themain condensers. These were followed by problems withthe heat exchangers, and then, with the piping.

Unit 3, which began operation in 1985, has both closed and opensections in its service water system with eleven titanium plate heatexchangers made by Alpha Laval as the interface between them.Since this unit is fairly new and since titanium was initially installedin both the heat exchangers and the condenser, there have been nosignificant corrosion problems to date. Corrosion problems with thepipe are anticipated when the rubber lining begins to crack or wear.

THE WATER

The brackish, polluted water used in the open, once-through por-tions of the service water systems is drawn from the Baltic Sea. Allthree units were tested two to three years before the unit start-up date

Table 2Water Description

Source Baltic SeaType brackish, pollutedTemperature 0 - 20'C (32 - 720F)pH 7.5 -8.0Chloride level 4,000 ppmMagnesium level 250 ppmCalcium 100 ppmSilica 0.8 ppm

any portion of the system. It is possible that the low water temper-ature during much of the year has prevented a MIC problem. Thewater source and description have not changed since initial testingof the system.

During July and August, crustaceans can accumulate in the system.At one time, a trial study was done in which hypochlorite was addedto the service water system to prevent crustacean growth. Althoughthis worked well, the use of hypochlorite additions was not adoptedby the plant because of environmental concerns. No additional chlo-rine or other chemicals are currently added to the water exceptduring system shut-down. A cathodic protection system is used toprevent deterioration of the condenser tubesheets and waterboxes.

MATERIAL EVALUATIONAND REPLACEMENT

Oskarshamn selects materials by reviewing technical literature, lab-oratory tests, and actual in-plant experience. The laboratory basedtesting program is sponsored by Vattenfall, the Swedish State PowerBoard, with financial support from participating power stations. Thetesting program simulates the corrosion and erosion problemscommon to the participating plants but at an accelerated rate. Thematerials included in the program are titanium, SAF 2507(UNS S32750) duplex stainless steel, 254 SMO (UNS S31254)and 654 SM0 (UNS S32654) austenitic stainless steels. All thestainless steels are produced by Avesta Sheffield AB. The samplesare evaluated on an annual basis. Oskarshamn also closely monitorsthe performance of those materials already in service during the reg-ularly scheduled inspection program.

Initial material replacement began in 1978 when a large number ofaluminum brass heat exchanger tubes in Units I and 2 were replacedwith titanium. The replacement program for Units I and 2 has beenon-going since that time. Subsequently, the rubber lining on thecarbon steel pipe began to crack (due to age) and wear away. As the

and may have had some stagnant water in them during that time.The basic characteristics of the water supply are outlined in Table 2.The high chloride content of the water and presence of pollutionwould be highly corrosive to many alloys. The increased solubilityof oxygen at lower water temperatures and the increased corrosionrates that normally result under these conditions are probably animportant contributing factor to the plant's problems. The facility isnot aware of any microbiologically influenced corrosion (MIC) in

Table 3Underground and In-Plant Replacement Materials

254 SMO 1984 1985 1986 1987 1988 1991 TOTALCOMPONENTS . _ _ 1

Pipe . 1 length i m 26 160 48 36 146'1' 42 458

ft. 85 524 157 118 479 138 1,500diameter mm 206-306 60-408 206 206 60-168 306

in. 8-12 2-16 8 8 2-7 12

Elbows 907 2 15 12 9 75 4

Cone Pipe Fttings 2 l l - | _

T-pieees l - | i 2

Condenser Tubeslength m - - 54,000 54,000

1t. - - 177.120 177,120diameter mm - - 24

ft. - - - . - 0.94

TITANIUM 1978 1979 TOTALCOMPONENTS

Condenser Tubeslenghth m 288.000 540,000

ft. 944,640 826,560 1,771,200diameter mm 24 25

in. 0.94 0.98

carbon steel is exposed to the service water, it corrodes quickly,making replacement of problem sections necessary. 254 SMO, a6% molybdenum stainless steel, has been the replacement materialof choice for pipe, tube and other system components since 1984because of its corrosion resistance, availability and strength.Although titanium also provides the necessary corrosion resistance,it is more difficult to weld than 254 SMO stainless. Increased inertgas shielding is required, and skilled titanium welders were difficultto obtain. The higher strength of 254 SMO stainless was also animportant factor in its selection.

Table 3 provides a summary of the titanium and 254 SMO stainlessinstalled to date at Oskarshamn. It should also be noted that smallamounts of 2205 stainless steel have been used in the past. Thismaterial is no longer used because of the problems experienced withcrevice corrosion in some of the flanges.

Und rgrovrnd anmd lui-PlcrnPiping

Since the service water enters the plant through culverts, there isvery little underground piping. Submerged pumps for the three unitspull the water from the culvert into short sections of undergroundpiping to bring it into the plant. The return pipes are submerged I m(3.28 ft) below the water surface to prevent foaming and splashingof the brackish water. The original underground and in-plant piping(including the emergency service water system piping) were carbonsteel with a rubber coating on both the outside and inside of thepipe. It was installed in the following years: Unit 1, 1969; Unit 2,1971; and Unit 3, 1982. As the rubber began to age and crack,Oskarshamn began to experience corrosion problems severe enoughto require pipe replacement. The same corrosion problems exist inboth the normal and emergency portions of the system. The rubbercracking and corrosion problem has been particularly severe in thecrevices of flange joints. The corrosion originated almost entirely onthe inside of the pipe.

In 1984, Oskarshamn started replacing sections of the undergroundpipe and the in-plant pipe in Units I and 2. 254 SMO stainless andtitanium were selected as replacement materials. No signs of corro-sion have been observed in subsequent pipe inspections, andOskarshamn is pleased with the performance to date. Both materialshave worked well, but, since they have found 254 SMO stainless tobe much easier to weld, it will be used for all future installations.The 254 SMO stainless has been the primary in-plant pipingreplacement material. A summary of the 254 SMO stainless pipingsizes, elbows, fittings and other components installed to date isshown in Table 3.

All of the in-plant piping system components are obtainable in254 SMO stainless.

It should be noted that there is still a great deal of rubber-lined pipein the plant. Replacement is occurring as necessary, when leaksappear or when detached sections of the rubber lining adverselyaffect the water flow rate.

Hoft Eicchvmgers

The original aluminum brass heat exchanger tubes were installed inUnits I and 2 in 1969 and 1971, respectively. Each of these unitshas over fifty shell and tube heat exchangers cooled directly by theopen portion of the service water system. The only closed loop

intermediate cooling system is in the reactor building. Unit 3 wasbuilt with only eleven plate heat exchangers exposed directly toservice water. It also has several closed loop intermediate coolingsystems for localized components which use demineralized water.Unit l's and Unit 2's heat exchanger tubes failed faster thananticipated because of the high water velocity. As of 1991, Unit 3'stitanium heat exchangers have not required replacement.

The tubes and tubesheets in fifty heat exchangers in Units I and 2have been replaced with titanium. To avoid the vibration problemswhich can be caused by the modulus difference, six support plateswere added to each "church window". The titanium has performedwell in this application, but, because of difficulties experienced inwelding titanium, 254 SMO stainless has been the replacementmaterial of choice for heat exchangers since 1984. The replacementof aluminum brass heat exchanger tubes and tubesheets is anongoing program.

Cond ensers

The original condenser tubes installed in Unit I in 1969 and Unit 2in 1971 were aluminum brass. Due to corrosion problems thatstarted within two to three years of installation, the condensers wereretubed in 1978 and 1979 with 544,000 m (1.77 million ft) oftitanium. The condenser tubesheets in Units I and 2 are carbon steelclad with Type 304 (18Cr-lONi) stainless steel, and, in Unit 3, theyare clad with titanium. The steam side of the outer most titaniumcondenser tubes in Units I sand 2 began showing signs of steamdroplet erosion as early as 1988. This has resulted in tube leakageand plugging of problem tubes. All the Swedish and Finnish powerplants with titanium condenser tubes have reported similarproblems. Frequent inspections of the outer tubes are done. OKGre-tubed the Unit 2 condenser with a total of 54,000 m (177,120 ft)of 254 SMO in 1991. Unit 3's original main condenser tubes aretitanium and have not had any problems to date.

SYSTEMR INSPECTION ANDCLEANING

Routine inspections are conducted by shift personnel as a part ofnormal plant operation. Water flow rates are monitored in thecentral control room and by local flow meters in the plant.Shift personnel look for leakage and other potential problems.In addition, the plant has a regularly scheduled maintenanceprogram which began in 1978 and has not changed significantlysince its inception. Cleaning and inspection of the system occursduring the annual refuelling outage. Whenever the system is shutdown, the system is flushed with "drinking" water, and ferrosulphateis added to any remaining brackish water to prevent deterioration.During outages, the culverts are drained and cleaned using highpressure equipment.

Much of the piping is still rubber-lined carbon steel. This is notgenerally inspected other than for through-wall leaks or for partialdetachment of the rubber lining which causes reduced flow throughthe pipe. If either problem exists, the section is replaced with254 SMO stainless. The sections which have already been replacedwith 254 SMO stainless, are inspected visually every five years inaccordance with the requirements of a 20-year warranty provided bythe manufacturer. The inspection is done by Oskarshamn personnel.

The aluminum brass seawater cooled heat exchangers in Units I and2 are cleaned and eddy current tested during the annual refuelingoutage. Since the titanium heat exchanger tubes have performedwell, they are cleaned and generally only visually inspected. Unit 3has a high pressure water strainer with 3 mm (0.12 in) filter holesinstalled behind the intake pumps to prevent crustaceans fromentering the system. Because of this, the titanium heat exchangers inUnit 3 are cleaned every five years. Suspended solids are notconsidered to be a problem in any of the units. Ball cleaningequipment is run continuously to keep the main condenser free ofbiofouling. %hen the system is stopped, the condenser is flushed anddried. Extensive testing of the titanium condenser tubes is requireddue to the erosion-corrosion problems that have occurred in the outerrows of tubes. Eddy current testing of these tubes is done annually.

The pumps are visually inspected every year. Normally, one out offour pumps is replaced with an overhauled unit so that each pump isoverhauled an average of once every four years. There is no formalprogram for inspecting valves, but, if a valve is temporarily removedfrom the system because of other repair work, it is inspected.

FABRI CATU ON

Since Oskarshamn currently uses only 254 SMO austenitic stainlesssteel, it will be the only material discussed. All the field and shopfabrication was done by an outside contractor. The welding proce-dure used by Oskarshamn was provided by the steel producer,Avesta Sheffield AB. The following is a brief summary of infor-mation provided. Several welding techniques are suitable: GasTungsten Arc Welding (GTAW or TIG); Gas Metal Arc Welding(GNIAW or MIG); or Shielded Metal Arc Welding (SMAW). Theweld pool should be protected from atmospheric oxidation by aninert gas cover. Preheating, hot spots, and post-weld heating are notrecommended and can be detrimental to the material properties.A filler metal with a chemistry equivalent to Alloy 625 isrecommended. The Oskarshamn plant used Avesta P- 12 filler metalwhich is produced by Avesta Welding. The interpass temperature ofthe work piece should not exceed 212' F (100C). This weldingprocedure is similar to the procedures recommended by otherproducers of 6Mo austenitic stainless steels. Flange joints were usedinstead of welding to join dissimilar materials.

Any heat tint should be removed after welding by either grindingwith a fine abrasive, by abrasive blasting with 75-100 micron soda-lime

glass beads, or by using pickling paste or pickling acid. Carbon steelbrushes are not allowed under any circumstances. Even commongrade stainless steel brushes are not suggested unless subsequentchemical cleaning of the weld is done. Brushing can potentiallycause iron contamination of the surface which may initiate pitting inan aggressive chloride environment.

CONCLUSIONS

The demanding service water environment that exists at theOskarshamn plant led the materials decision makers to use and gainexperience with highly corrosion resistant materials. This large scale,long-term experience with titanium and a 6Mo austenitic stainlesssteel in a highly demanding service water system environmentprovides valuable assistance to materials decision makersencountering similar problems. Titanium; the duplex stainless steel,2205; and the 6Mo austenitic stainless steel, 254 SMO, have all beenused as replacement piping materials in the plant. Titanium hasperformed well in all applications except the outermost rows of thecondenser tubes, but, due to problems associated with welding,Oskarshamn does not plan to use titanium in the future. Crevicecorrosion problems with 2205 eliminated it from futureconsideration. The preferred replacement material since 1984 hasbeen the 6Mo austenitic stainless steel alloy 254 SMO because of itscorrosion resistance, availability, relative ease of fabrication, andstrength. Although 254 SMO is the only 6Mo austenitic to have beentried, it is assumed that the other alloys in this family would alsoperform well. Two alloys that are currently being tested, SAF 2507duplex stainless steel and 654 SMO austenitic stainless steel, may beconsidered for future installations.

The 6Mo austenitic stainless steels are readily available in all thecommon product forms needed in constructing a service water system.This makes it possible to replace all existing system components toprovide maximum system cost effectiveness and efficiency. Sincethere are several 6Mo austenitic stainless steel alloy producers fromwhich to choose, materials specifiers can generally select from avariety of sources based on the properties and components required,quality, technical support, service, delivery, and price.

We ackinowledge the assistance of Al r Fredrik Baniekow of OKGA&7IEBOLAG lio tas indispensable in this project 'S success. AIrBarnek-ow prnwided the infonnation used in this case study andretviewed thefinal case stut 'for accuracy.

........................................................................................................................................................................................................................................

OFFICES OF THE NICKEL DEVELOPMENT INSTITUTE

North America Japan Mehrauli-Badarpur Road Material has been prepared for the214 King SLW., Suite 510, Toronto, - 113. 5-chome, Shimbashi, New Delhi 110 062, India general Information of the reader andOntario. Canada MSH 3S6. Minato-ku, Tokyo, Japan Tel. 91 11 698 0360 should not be used or relied upon forTel. 1 416 591 7999 Tel. 81 3 3436 7953 Fax. 91 11 698 9522 specific applications without first secur-Fax. 1 416 591 7987 Fax. 81 3 3436 7734 AustralastIng competent advice. While the materi-Fax.uro416pe 917987 Fax. & South 3436 ric Australasfa al Is believed to be technically correct,Europe Central & South America P.O. Box 28. Blackburn South NiDI, Its members, staff end consultants42 Weymnouth St. cto Instituto de Metais Nao Ferrosos Victoria 3130. Australia do not represent or warrant Its suitabili-London, England W1N 3LO Av.9 de Julho. 4015 Tel. 613 9878 7558t o n enerao spefic us anTel. 44 171 493 7999 01407-100 Sao Paulo-S.P., Brasil Mobile 61 18 346 808 ty any general or specific use endFax. 44 171 493 1555 Tel. 55 11 887 2033 Fax. 613 9894 3403 any kind n connection with the infoma-European Technical Information Centre Fax. 5511 885 8124 South Korea ton herein.The Holloway, Alvechurch India Olympia Building -Room 811Birmingham, England B48 70B co India Lead Zinc Information Centre 196-7 Jamsilbon-Dong, SongpaKu,Tel. 44152 758 4777 Jawahar Dhatu Bhawan Seoul 138 229, South KoreaFax.44 152 758 5562 39 Tughlaqabad Institutional Area Tel. 82 2 419 6465

Fax. 82 2 419 2088

Feb 96/2.5

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he material presented inthis publication has beenprepared for the generalinformation of the readerand should not be used orrelied on for specificapplications without firstsecuring competent advice.The Nickel DevelopmentInstitute, its members, staffand consultants do notrepresent or warrant itssuitability for any general orspecific use and assume noliability or responsibility ofany kind in connection withthe information herein.

Reprinted from CHEMICAL ENGINEERING, January 1990, copyright 1990 by McGraw Hill, Inc. with all rights reserved.Additional reprints may be ordered by calling Chemical Engineering Reprint Department (212) 512-3607

THE RIGHT METAL FORHEAT EXCHANGER TUBES

Arthur h. Tuthill,*Tuthill Associates Inc.

W ^ When designing a heat exchang-er, an engineer first calculates

km *the surface area needed to car-ry the heat load. Next, he or she devel-ops the design to meet the standards ofthe Tubular Exchanger ManufacturersAssn. (TEMA) for heat exchangers, orother codes, and the company's stan-dards. He or she then makes compara-tive cost estimates, factoring in knowl-edge from experience, and selects thebest tubing metal for the service.

Most unexpected failures of heat ex-changers can be traced to a factor thathad not been fully taken into accountwhen the tube material was selected. InTables 1, 2 and 3, these factors arearranged according to, respectively,water quality, the character of opera-tion and maintenance, and exchangerdesign. Tube materials considered arecopper alloys, stainless steels (Types304 and 316), and high alloys (6% molyb-denum, superferritics* and titanium).

Attention to this checklistof selection factors will materiallyreduce heat-exchanger failures

The impact of each factor is notedwithout it necessarily being related tothat of other factors. In the tables, theimpact of each factor is rated one ofthree ways: green means the tubingalloy or alloy group has given goodperformance under the stated condi-tions; yellow designates that the tub-ing may give good performance, butmay require a closer study of the con-ditions at the site and relationshipswith other factors; and red signifiesthat the material has not performedwell under the stipulated conditions,and special precautions are required toachieve good performance.

Water qualityWater quality encompasses: cleanli-ness, and the content of chloride, dis-solved oxygen and sulfides, and resid-

ual chlorine and manganese. It alsoincludes pH, temperature and scalingtendency (Table 1).

Water cleanliness-Design engi-neers tend to assume that cooling wa-ter will be clean. This occurs only if theright screens and filters have beeninstalled and operators have madesure that they work properly. Debris(such as sticks and stones) and sedi-ment (such as sand and mud) that arepassed through or around the screensand filters have been responsible formany tube failures.

Long term, copper-alloy and stain-less-steel tubes perform excellently inclean water (i.e., free of sediment, de-bris and fouling organisms). Too often,however, sediment and debris findtheir way into exchanger tubes. Corro-sion under sediment is common withtubes of these two materials. A high*A new family of stainless steels high in chromium content (25-30%).

"Consultant to the Nickel Development institute, 15 Toronto St, Toronto, Ontario, Canada

I

1. Water cleanlinets; -Sedimfe

concentration of sand can abrade theprotective film on copper-alloy tubes.tSuch service, therefore, requires a 70-30 CuNi-2Fe-2Mn alloy in the copper-alloy series, or stainless steel. A lodg-ment of sticks, stones and shellfragments creates downstream turbu-lence, which can cause pinholes in cop-per-alloy tubes.

The obvious cure for these problemsis to screen the water better. As asafeguard, the newer 85-15 CuNi with0.5 Cr, C72200 alloy and stainless-steeltubes do well in withstanding the ef-fects of lodgment turbulence. Copper-alloy tubes effectively keep organismsfrom becoming attached, and are pre-ferred when environmental restric-tions on the use of biocides would re-quire frequent manual cleaning ofstainless-steel and higher-alloy tubes.

Chlorides - These provide a conve-nient framework for differentiatingthe stainless-steel alloys. Type 304stainless steel resists crevice corrosionat chloride-ion concentrations of lessthan about 200 ppm, and Type 316 doesso at levels up to about 1,000 ppm. (Thechloride content of U.S. fresh water istypically less than 50 ppm, for whichType 304 stainless steel is thereforenormally adequate.)

The 42% molybdenum alloys suf-fer crevice attack at chloride-ion con-centrations from 2,000 to 3,000 ppm.Both 4'/2% molybdenum-alloy and du-plex (another new family of stainlesssteels) tubes have been subjected tosea water (20,000 ppm chloride con-tent) and have undergone substantialcrevice corrosion beneath fouling. Onthe other hand, the 6% molybdenumand superferritic alloys, and titaniumhave proved resistant to crevice andbeneath-sediment corrosion in saltwater.

Dissolved oxygen and sulfides -Copper-alloy and stainless-steel tubesperform best in water having enoughoxygen (about 3-4 ppm) to keep fishalive. These tubes also do well in de-aerated water, such as that used inwater-flood oil wells. Copper-alloytubes do not stand up well in severelypolluted water in which dissolved oxy-gen has been consumed in the decay

Tuibem e t alz :\ \C A0::;0~:

ftia:s :s00:

Clean Mud

f | - ill n1-l ~ czzEiz D E :7e-

rn~;:+ :;j f :\;; I: \00 I:B iolgicalSand0 : 0:f;00 D e~b ris \ f\t untsz h zId -:lED -Si d X\:: n

C A = CO pper * a X SS St in ess steel

tAll alloys form a protective film in corrosive liquids; onstainless steel, it is chromium oxide; on copper alloy, it iscuprous hydroxychloride.

process and sulfides are present.Tubes of higher-alloyed stainless steelor titanium have served successfullyin such water.

Residual chlorine - Both copper-al-loy and stainless-steel tubes have per-formed well in water containing up to 2ppm residual chlorine, and have failedin heavily chlorinated water. Althoughthe usual objective is to keep residualchlorine at about 0.5 ppm at the inlettubesheet, this level is sometimes ex-ceeded and the residual is normallyhigher at the point of injection.

Acidity -In aerated water of pHless than about 5, a protective filmdoes not easily form on copper-alloytubes, so they corrode and thin rapidly.In deaerated water of low pH, copper-alloy tubes resist corrosion well. Forhigh-pH water, copper-nickel or stain-less-steel tubes are preferred to admi-ralty- (71% copper, 28% brass, 1% tin)or aluminum-brass tubes, which tendto corrode under highly alkaline condi-

Leaving anexchanger full,

or even onlywet, invitescorrosion

ever, copper-alloy and higher-alloyedtubes have fared well in such water.

Scaling tendency - Copper-alloyand stainless-steel tubes perform wellin both hard (scaling) and soft (nonscal-ing) water. The Langelier saturationindex* is frequently used to distinguishscale-forming from corrosive (to carbonsteel) water.

Operation and maintenanceAmong these factors are type of oper-ation (regular vs. intermittent) and thefrequency of cleaning (Table 2).

ment in which bacteria thrive, promot-ing microbiologically induced corro-sion. Corrosion will also take place un-der sediment. If an exchanger is to beleft full for more than 2 or 3 days,water should be pumped through itonce a day to displace the stagnantwater. If an exchanger will be downfor at least a week, it should be drainedand blown dry.

Cleaning schedule - Heat ex-changers should be periodicallyflushed out, opened and brush cleaned,to remove sediment and debris and torestore heat transfer capability. Ex-changers handling water high in bio-logical foulants or sediment should becleaned weekly. Micro-organisms willcorrode stainless steel if they and oth-er deposits are not removed.

Monthly or even quarterly mechan-ical cleanings of copper-alloy andstainless-steel tubes are adequatewith most waters. The optimum in-terval can be critical because the pro-tective film on copper alloy tubes canbe damaged by cleaning with metallicbrushes and some types of abrasiveblasting. Mechanical cleaning issometimes put off for a year, andeven longer, particularly if restoringan exchanger's heat-transfer rate isnot critical to plant performance. Becautioned, however, that corrosionbeneath sediment frequently occurswhen sediment removal is delayed bymore than three months.

Exchanger designThe principal design factors that in-fluence tube performance are watervelocity, tube diameter, shape (i.e.,once-through or U-bend), orientation,venting, tubesheet material, channel(waterbox) material and channel inletarrangement (Table 3).

Fluid velocity - At velocities ofless than 3 ft/s, sediment deposit, de-bris buildup and biological fouling inand on tubes can be excessive, result-ing in the need for frequent mechani-cal cleaning, which can cause copper-alloy and stainless-tube tubes to failprematurely.

Copper alloys can be convenientlydifferentiated according to their wa-ter-velocity tolerance. Approximatemaximum design velocities for tubesof copper-base alloys and stainless

tions. Stainless-steel tubes have per-formed well at a pH less than 5 andgreater than 9.

Temperature-A protective filmreadily forms on copper alloys in warmwater (in about ten minutes at 60TF), butforms very slowly in cold water. It de-velops almost instantaneously on stain-less steel in both warm and cold water.

Manganese - Type 304 stainless steeltubes have failed in fresh water having anappreciable manganese content. How-

Character of operation - Lengthystartups have been responsible formany failures of copper-alloy andstainless-steel tubes. These occurredbecause water had been left in, or ithad only been partially drained from,tubes for a long time. Such failureshave also been caused by extendedoutages from normal operations.

Leaving an exchanger full, or evenonly wet, invites corrosion. The waterwill become foul, creating an environ-

'This index indicates the tendency of a water solution to precipitate or dissolve calcium carbonate. It is calculated from totaldissolved solids, calcium concentration, total alkalinity, pH and solution temperature.

steel in salt water are listed in Table 3.Maximum velocity is usually arrivedat as a compromise between the costof pumping and the advantage in heattransfer. The design velocity usuallyfalls in the range of 6-8 ft/s, and mayreach 12-15 ft/s when extra coolingdemand is placed on an exchanger,such as in summer.

Copper-nickel tubes stand up reason-ably well to variations in velocity, al-though some erosion and corrosionmay occur at the inlet. The C72200 alloyresists inlet-end erosion and corrosion,as well as corrosion downstream oflodgments. The 2Fe-2Mn modificationof the C71500 alloy resists inlet erosionand corrosion excellently. Copper-nick-el tubes, after their protective film hasaged, withstand considerable velocityexcursions without significant inleterosion. Stainless-steel tubes performbest at high velocity and are useful upto velocities that induce cativation. Cop-per will tolerate somewhat higher ve-locities in fresh water, 10 ft/s being acommon design velocity for coppertubes in air-conditioning condenserscooled with fresh water.

Tube diameter - Tubes of large di-ameter are preferred for heat ex-changers because any solids that passthrough screens will also flowthrough the tubes. By one rule ofthumb, tube diameters should be atleast twice the diameters of thescreen openings. Tubes should not beless than Y2 inch if the water to theexchanger is not filtered.

Once-through or U-bend - Be-cause U-tube bundles are difficult toclean, the water must be very clean(e.g., boiler feedwater quality), or atleast well-filtered. Both stainless-steel and copper-alloy tubes are liableto corrode beneath sediment. U-tubesare particularly prone to such corro-sion if sediment and debris are notremoved from their bends. Once-through and 2- to 4-pass bundles areeasily cleaned by flushing, water lanc-ing, or brushing.

Orientation - Heat exchangers,particularly condensers, are normallyplaced horizontally, with water flow-ing through the tubes. Both stainless-steel and copper-alloy tubes performwell in such exchangers. In those un-usual circumstances that require that

the cooling-water flow on the shell-side of a horizontal exchanger, sedi-ment and debris cannot be kept frombuilding up around the support platesand lower tubes. This results in corro-sion beneath the sediment. The build-up can be eliminated, or at least re-strained, by upstream filters, butthese will not prevent fouling organ-isms from thriving in low-flow areas.When the water, even clean water,must be on the shellside, the tubesshould be of high alloy.

A condenser is sometimes orientedvertically, with the cooling water onthe shellside, to improve heat trans-fer. This allows noncondensable gas-es to collect under the top tubesheet,

TEMA strecommend tt

be installethey should re

letting the temperature of the tubewalls in the gas pocket get almost ashot as the incoming gas being con-densed, evaporating the water and de-positing scale on the hot tube sur-faces. Sediment also tends to build upin the bottom of a vertical condenser.

In vertical installations, both Type304 and Type 316 stainless-steel tubesare prone to stress corrosion andcracking just under the top tubesheet.Remedies include: venting gasthrough the top tubesheet; changingto copper-alloy or copper alloy-stain-less steel bimetallic tubing or to high-alloy tubing, or orienting the ex-changer horizontally. Although theTEMA standards recommend that ex-changers be installed level, exchang-ers should really be sloped slightly sothat they will drain completely whenshut down, avoiding corrosion wheretubes sag between support plates andretain water even after being drained.

Venting - Exchangers are normal-ly fitted with vent cocks so they canbe purged to clear gas pockets. Con-densers, particularly when chlorine isused as a biocide, tend to suffer corro-sion when gases are not vented.

C

Car

Tubesheet material-Tubesheetsof carbon steel, common copper alloy,Muntz metal (a brass composed of 58-61% copper, up to 1% lead, with theremainder zinc), admiralty brass andaluminum bronze are anodic to cop-per-alloy tubes. The galvanic protec-tion that these tubesheet materialsafford copper-alloy tubes does noteliminate all inlet-end corrosion, butoften does help to keep it at a tolera-ble level.

Stainless-steel tubesheets are rarelyused with copper-alloy tubes, becausestainless steel is cathodic to copperalloy. Installing stainless-steel or tita-nium tubes in copper-alloy tubesheetshas accelerated the corrosion of the

3ndardsat exchangersI level, butally be sloped

tubesheets. Stainless steel and titani-um polarize so readily that the entireinside surface of the tubes (not just thepart adjacent to the tubesheet) mustbe considered as the cathode to thecopper-alloy tubesheet anode.

The normal cure for this anode-cathode problem is to protect the cop-per-alloy tubesheet with an im-pressed-current cathodic protectionunit. The unit's potential must be con-trolled to avoid hydrogen embrittle-ment of ferritic stainless steel, or by-driding of titanium. An alternative isto resort to tubes of 6-molybdenum,which resist hydrogen embrittlementwithout the need to carefully controlan applied potential.

Tubesheets for austenitic stainlesssteel should be of identical composi-tion. Tubesheets of high-alloy austen-itic stainless steel are used with tubesof ferritic stainless steel, because tu-besheets of matching composition arenot available. Solid or clad titaniumtubesheets are preferred with titani-um tubes.

Channel material - Corrosionproducts from bare-steel and cast-ironchannels (exchanger inlet chambers)

have occasionally caused the corro-sion failure of copper-alloy and stain-less-steel tubes. Coatings applied tosteel and cast-iron channels for thepurpose of reducing corrosion some-times deteriorate and spall, leading totube corrosion and failure. Coatedchannels are also liable to deep localcorrosion at pinholes in coatingsbrought on by an adverse galvaniccouple between the steel channel andthe alloy tube and tubesheet.

Copper-nickel and aluminum-bronze (solid or weld-overlaid surface)channels are preferred with copper-alloy tubes, and may also be used withhigh-alloy tubes. The adverse galvan-ic effect is diminished in such installa-tions, because the area of the channelis larger than that of the tubesheet,and the channel and tubes are notcontiguous. Channels of Type 316stainless steel (solid or overlaid) arepreferred with stainless-steel tubes.

Channel inlet arrangement - Un-even flow, restricted water passagesand poor inlet-piping entry arrange-ments have caused numerous failuresof copper-alloy tubes, as well as a fewfailures of stainless-steel tubes. Basi-cally, the entry and flow pattern in bothlarge and small channels should distrib-ute the water uniformly to all tubeswith as little swirling as possible.

If a review of the foregoing factorsindicates that an exchanger's tubesmust be of a metal that is even morecorrosion resistant than a copper alloyor stainless steel, an engineer fre-quently resorts to a more highly al-loyed metal, such a 6-molybdenumstainless steel, a superferritic or titani-um. These materials provide outstand-ing resistance to corrosion in crevicesand beneath sediment. a

The authorArthur H. Tuthill, a materialsand corrosion consultant (2903Wakefield Dr., Blackburg, VA24060; tel.: 703-953-2626), has had extensive experience in thefabrication, use and perfor-mance of metals, particularly involving heat exchangers, pip-

ing and pumps, in a vde ranein metallurgical engineering from Carnegie-Mel-lon University and a B.S. in chemical engineeringfrom the University of Virginia, he is a licensedengineer (metallurgy). Among the many articlesthat he has had published is a five-part series inChemical Engineerin: "Installed Cost of Corro-sion-Resistant Piping (Mar. 3 and 31, Apr. 28, May26 and June 23, 1986).

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The material presented inthis publication has beenprepared for the generalinformation of the readerand should not be used orrelied on for specificapplications without firstsecuring competent advice.

The Nickel DevelopmentInstitute, its members, staffand consultants do notrepresent or warrant itssuitability for any general orspecific use and assume noliability or responsibility ofany kind in connection withthe information herein.

Specifying

STAINLESS STEELSurface Treatments

Though stainless steel is naturallypassivated by exposure to air andother oxidizers, additional surfacetreatments often are needed toprevent corrosion.

Arthur H. Tuthill*,Blacksbtirg, Va.,

Richard E. Avery*,Londonderry, N.H.,Consltants to Nickel Development Institute

ing shop dirt, iron particles from cutting tools,and machining lubricants. Passivation treat-ments of stainless steel with nitric or mild or-ganic acids are useful mild cleaning operationsperformed after machining to enhance theprotective nature of the natural, air-formed film.Nitric acid treatment enhances the level of chro-mium in the protective film on stainless steels.2DeBold has published an excellent practicalreview of nitric acid passivation of stainless steelmachined parts.3

ASTM A 380 describes eight nitric-acid-basedcleaning/passivation treatments and four clean-ing treatments using other chemicals. None ofthese passivation treatments corrode or etch thesurface. Several are designed to clean bright orpolished surfaces by removing loosely adherentforeign matter. The most common treatment is

Handle with care

assivation, pickling, electropolishing,and in some circumstances, mechanicalcleaning, are important surface treat-ments for the successful performance of

stainless steel used for piping, pressure vessels,tanks, and machined parts in a wide variety ofapplications. Among them: pulp mills, nuclearpower plants, hospital sterilization systems, foodprocessing equipment, biotechnology processingplants, breweries, electronic-chip washingfacilities, swimming-pool hardware, water treat-ment plants, and chemical process plants.

Determining which treatment should be usedfor specific applications is confusing to manyspecifiers. A good place to start is with ASTM A380-88, "Cleaning and Descaling Stainless SteelParts, Equipment and Systems,"' an excellentresource document for the cleaning of stainlesssteel, although it does not cover electropolishing.

Passivation treatmentsExposure to air is the natural, primary pas-

sivation treatment for stainless steel. This ex-posure produces a thin, durable chromium-oxide film that forms rapidly on the alloy surfaceand gives stainless steel its characteristic "stain-less" quality. Exposure of the surface to water orother oxidizing environments also produces thispassivating film.

Additional passivation is called for in manyspecifications to remove light surface contamina-tion from machined stainless steel parts, includ-Member ofASM International

Most surface defects on stainless steel that aredifficult to remove and, thus, contribute to cor-rosion, are produced during fabrication. Com-mon defects include embedded steel particles,heat tint, arc strikes, weld spatter, grind marks,scratches, and organic contamination frommarking crayons and paint. All of these tend toinitiate corrosion that would not occur in theirabsence, and will accelerate localized corrosionin aggressive environments.

Embedded iron: The surface of stainless steelwill pick up particles of carbon steel from steellayout and cutting tables, forming rolls, carbonsteel wire brushes, sandblasting, grinding, andfrom handling with steel slings and clamps.Sheet and plate should be stored in vertical racksto avoid scoring that can take place with floorstorage.

Steel particles embedded in the surface ofstainless steel will rust when they are exposed towater or a moist atmosphere, showing up asspots and streaks which, if not removed, canproduce pitting.

Heat tint: Welding heats the base metal, caus-ing heavy oxide films (scale) to develop in theheat-affected zone (HAZ). These oxide filmsrange in color from light brown to black.

Removing heat tint is costly, and may be un-

1

immersion in a 20 to 40% solution of HNO3 at atemperature of 50 to 60'C (120 to 140'F).

The complete passivation treatment includesdegreasing, immersion, and rinsing. Degreasing,preferably in a nonchlorinated solvent, removesorganic contaminants from the surface.

Degreasing: Neither air nor nitric acid canform or enhance the protective film when grease,oil, fingerprints, or other organic contaminationare present on the surface. Parts must bethoroughly degreased prior to any passivationtreatment. The water-break test, described inASTM A 380, is easy to apply and is effective indetecting residual organic matter that may nothave been removed in the degreasing operation.A sheet of water directed over the surface will"break" around oil, grease, and other organiccontaminants not completely removed from thesurface. Specifications can simply call for nobreak in the film as it drains from the verticalsurface.

Immersion: The part is immersed in a pas-sivating solution selected from ASTM A 380Table A2.1, Part II or Part III. In addition to thestandard HNO3 solution, there are a number ofsolution variations appropriate for all grades of200, 300, and 400 series, maraging, precipitationhardening and free-machining alloys in variousheat treat conditions and surface finishes.

Rinsing: Immediate and thorough rinsing inclean water of pH 6 to 8 is mandatory, In manyinstances neutralization prior to rinsing is help-

Rust in the heat-affected zone of this weld on a stainless steel pipe (darkbands on both sides of the weld) was produced by iron embedded in the sur-face during wire brushing. Rust spots awayfrom the weld were caused byparticlesfrom an overhead sandblasting operation thatfell on the pipe.

ful. Immersion, neutralization, and rinsing mustfollow one another without allowing the surfaceto dry between steps. When passivating stainlesssteel sheet material, each sheet must be com-pletely dry before it is stacked to avoid watermarks.

In addition to the cleaning precautions givenin ASTM A 380, different grades of stainless steelshould not be mixed in the same passivatingbath as this can initiate corrosion where surfacescome in contact.3

Although nitric acid does not normally cor-

necessary if stainless steel is exposed only towater, alkaline environments, and other mild in-dustrial atmospheres, which seldom initiate cor-rosion. However, removal of heat tint may benecessary to prevent corrosion in acidic environ-ments, especially when the base metal has verylittle extra corrosion resistance. In some mild en-vironments, heat tint removal is necessary toprevent contamination of process fluids.

Heat tint must be removed when scrupulous-ly clean surfaces are required to prevent con-tamination and batch-to-batch carryover ofprocess materials. These applications includeevaporators and piping for high-purity andultrahigh-purity water systems, nuclear piping,pharmaceutical and biological equipment,electronic-chip washing facilities, and breweryequipment.

Weld flux: Weld flux, produced by weldingwith covered electrodes, is difficult to removecompletely, especially from the sides of the weldbead. Wire brushing with stainless steel wirebrushes, abrasive disk and flapper wheel grind-ing, and chipping may leave small flux particlesat the side of the bead. These particles are excel-lent crevice formers, and their complete removalgenerally requires pickling or electropolishing.

Arc strikes and spatter Arc strikes produce

These common surface defects on stainless steel allresultfrom mechanical operations that are used tofabri-cate components.

small pinpoint surface defects in the protectivefilm, as does weld spatter. If defects cannot beprevented, they should be removed before plac-ing stainless steel into service in aggressive en-vironments.

Scratches and paint Deep scratches also in-itiate corrosion, as can paint crayon marks, andother instruction markings if they are notremoved.

2

rode stainless steel, it will corrode surfaces thatare significantly altered. Acid cleaning shouldnot be used for carburized and nitrided stainlesssteel parts nor for improperly heat treated high-carbon/high-chromium martensitic grades thathave not been fully hardened.3

Pickling treatmentsPassivation treatments are not designed to

remove heat tint, embedded iron particles, heattreating scale, and other surface defectsproduced during fabrication, since nitric aciddoes not corrode or remove the surface layershaving embedded defects. Elimination of thesedefects requires removal of the normal, protec-tive oxide layer and 25 to 40 pm (0.001 to 0.0015in.) of the substrate metal by pickling the surfacein a nitric-hydrofluoric acid (HNO,-HF) bath.The protective film then reforms in air over thefreshly cleaned surface. This oxide film isuniform and leaves the stainless surface in itsnormal passive condition.

While pickling is not strictly a passivatingtreatment, it provides many of the same benefits.Pickling is most useful for localized cleaning ofwelded areas, but also can be used to improvethe corrosion resistance of mechanically cleanedsurfaces.

Disposal of pickle liquor is a growing prob-lem that tends to limit pickling by immersion tothose fabricators and chemical cleaning contrac-tors who already have pickle tanks and ap-proved arrangements for disposal.

Pickling at the steel mill removes the oxidescale that forms during annealing. Mill picklingalso removes manganese sulfides or other inclu-sions in the surface and removes surface layersthat may have been depleted in chromiumduring annealing.

ASTM A 380 lists three pickling solutions forstainless steel. Fabricated austenitic stainlesssteels can be pickled by immersion in a standard10% HNO3 , 2% HF bath at 50'C (120TF). For localarea pickling or if the fabricated component istoo large to be immersed, commercial HNO 3 -HFpickle pastes can be just as effective. Pickle pastecan be applied with a paint roller or nylon brush.

Paste must be washed off within 15 to 30 minof application, or corrosion will be initiated. Per-sonnel need protective clothing and training insafe handling procedures.

Although post-fabrication pickling improvesthe performance of stainless steels in a variety ofapplications, until recently there has been verylittle research data to support field experience.Quantitative data on the increase in critical pit-ting temperature in ferric chloride (ASTM G 48)shows that pickling provides a 2.5 to 10'C (4.5 to18TF) improvement in performance.' While notlarge, the improvements in lightly ground, andglass-bead blasted surfaces are uniformly posi-tive, indicating that pickling provides benefitsbeyond those obtained with the best controlledmechanical treatments.

Crevice corrosion can be initiated by deep scratches, top and by paintand other markings, such as those made by a marking crayon, bottom.Removal of the markings would have prevented the corrosion.

The heat-affected zone on the opposite side of a weldcan also initiate corrosion f the heavy oxidefilm (scale)is not removed. For example, the corrosion shown here ison the inside of a vessel, in the heat affected zone of anexternal weld.

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Original surface Pickled Ground Ground(IlNOYHF) (60 grit) and pickl

Base metal - 6%,f, Mo stainless steel Cronifer 1925hNfo (Krupp-VDNI AG)

I Pickled with Glass-bead Glass-beaded commercial blasted blasted

paste and pickled

Pickling of stainless steel increases the critical pitting temperatire in ferric chloride (per ASTM G 48) in the basemetal, heat-affected zone, and weld areas. Mechanical cleaning treatnents that are performed without a succeedingpickling treatment decrease tire critical pitting teiperatire.

Electrocleaning and electropolishingElectrocleaning, an electropolishing techni-

que, is a useful alternative to pickling treat-ments. Although electrocleaning is not coveredunder ASTM A 380, it is widely used to removeimperfections from the surface of stainless steelafter fabrication. It removes embedded iron par-ticles and similar film defects as does pickling.Unlike pickling, electrocleaning does not rough-en the surface, but makes it smoother. A 12-Vdcpower source with variable current capability isconnected to the stainless steel, making it theanode. A copper cathode and an electrolyte -usually phosphoric acid - are then used to cor-rode away the protective film and several layersof the surface in a controlled manner by varyingthe current and dwell time.

Electrocleaning can be performed in mostplating shops by immersion. Localized electro-cleaning with field kits is widely practiced to re-move heat tint and weld-related defects from theheat-affected zone.

Electropolishing is the same process as elec-trocleaning, but is generally performed for alonger time. It is used to polish large surfaces.One use is the polishing of pulp mill headboxesto prevent pulp hang-up on tiny surface imper-fections. It is also used in the electronics andbiotechnology industries to clean and smooththe inside surfaces of pipe and tubing. Largenuclear power plant components also are elec-tropolished to refurbish contaminated surfaces.

Electrolyte

Copper CathodeInsulated

\,~lp ;. Z f,...^ handleNylon sponge .-; . h n dl

Stainles te

Direct-currentAnode power source

Picklingremovesheat tintandembeddedsiurfaceCo i-taininants.

Localized electrocleaning of heat titfromi the surfaceof stainless steel can be performed with a simple toolsuch as the one shown here.

Electropolishing, because it uses milder acidsand can be performed locally, reduces the vol-ume of waste liquor for disposal compared withimmersion pickling. However, personnel mustbe protected and disposal regulations must beobserved, as is done in other pickling, passi-vating, and electrocleaning operations.

Since both pickling and electropolishing re-move metal, neither process can be used onpolished surfaces without altering the surfacefinish. Care should also be used when picklingor electropolishing machined surfaces. Althoughonly about 25 gm (0.001 in.) of the surface is cor-roded away, this may be enough to alter toler-ances on some closely dimensioned parts.

Mechanical cleaningSection 5.3 of ASTM A 380 describes mechani-

4

Mechanicalcleaning

procedurescan do

more harmthan good.

cal descaling methods commonly used to cleanwelds. These include abrasive blasting, brushing,grinding, and chipping. However, if thesemechanical cleaning procedures are not per-formed carefully, they can do more harm thangood.

Grit blasting can be extremely detrimental asit is almost impossible to prevent particles of gritfrom becoming embedded in the surface beingblasted. Grit blasting also roughens the surfaceto the point where crevice corrosion becomeslikely. Peening with clean stainless steel shot,which produces compressive stresses in the sur-face, reduces the risk of stress corrosion crackingin some applications. However, this must bebalanced against the increased risk of crevicecorrosion due to the roughened surface.

Sand blasting should be avoided unless noother cleaning method can be used. This is oftenthe case when cleaning stainless steel tank bot-toms that have been inadequately protectedfrom contamination during construction. Onlynew, uncontaminated sand should be used, andthen only once.

Blasting with clean glass beads is an effectivemethod for local- and large-area cleaning. Cleanwalnut shells also are a useful blasting medium.

Grinding with clean aluminum oxide disks orclean flapper wheels can be used to remove heattint and other weld-related defects. However,even light grinding leaves a cold worked,

smeared surface that has microcracks, laps,seams, and other sites that can initiate crevicecorrosion in aggressive environments. Heavygrinding with grinding wheels overheats thesurface of stainless steel and degrades its cor-rosion resistance to depths greater than the 25 to50 gm (0.001 to 0.002 in.). As a result, grindingshould be used only when removal of the weldreinforcement (weld crown) is more importantthan optimizing corrosion resistance.

Chipping is normally used between weldpasses to remove weld slag, and subsequentweld passes normally eliminate any damagingeffects.

Inspection proceduresSeveral methods of evaluating cleanliness

after fabrication are described in ASTM A 380.The water-break test described previously isused to determine whether organic contamina-tion has been removed from the surface. Wateralso is useful in detecting iron contamination:rust streaks and spots will form on wetted sur-faces over a period of several hours if con-tamination is present.

The copper sulfate and ferroxyl tests are muchmore sensitive than the water test, and arespecified when the surface must be entirely freeof iron. Special considerations apply when test-ing equipment intended for use with food,beverages, or other products for human con-sumption. The ferroxyl test is effective and easyto use, although the solution does not have along shelf life. U

For more information: Contact Mr. Arthur H. Tuthill,P.E., at Tuthill Associates Inc., P.O. Box 204, Blacks-burg, VA 24060 (tel: 703/953-2626; fax: 703/953-2636),or Mr. Richard E. Avery at Avery Consulting As-sociates Inc., 117 Winterwood Dr., Londonderry, NH03053 (tel: 603/434-2625; fax: 603/425-2542).Information on stainless steels can be obtained from theNickel Development Institute, 214 King St. W. Suite 510,Toronto, Ontario, Canada M5H 3S6 (tel: 416/591-7999;fax: 416/591-7987). Copies of ASTM A 380-88 can beordered from the American Society for Testingand Materials (ASTM), 1916 Race St., Philadelphia, PA19103-1187 (tel: 215/299-5400; fax: 215/977-9679).References1. "Cleaning and Descaling Stainless Steel Parts,Equipment and Systems": ASTM A 380-88, AmericanSociety for Testing and Materials Philadelphia, Pa.2. "An X-Ray Photo-electron Spectroscopic Study ofSurface Treatments of Stainless Steels," by K. Asamiand K. Hashimoto: Corrosion Science, Vol. 19, 1979, p.1007-1017.3. "Passivation of Stainless Steel Parts," by T. DeBold:TAPPI Journal, January 1988, p. 196-198.4. Dr. Rockel, Krupp VDM GmbH, private com-munication.

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The material presented inthis publication has beenprepared for the generalinformation of the readerand should not be used orrelied on for specificapplications without firstsecuring competent advice.The Nickel DevelopmentInstitute, its members, staffand consultants do notrepresent or warrant itssuitability for any general orspecific use and assume noliability or responsibility ofany kind in connection withthe information herein.

Design, water factorsaffect service -water* piping materialsThe effects of design, water quality, and watercomposition factors on the performance of alloyand carbon steel nuclear piping are reviewed

ing damage from the inside of the pipe.Many expedients have been tried to repairlining damage in piping smaller than 36in. but none have proved completely suc-cessful.

Municipal water distribution systemsand utility raw water intake systems arecharacterized by long straight runs of sev-eral hundred feet with 20 feet or morebetween joints or welds. Shipboard,chemical plant and nuclear service waterpiping systems are characterized by shortruns, frequent bends and numerous valvesand fittings.

It is difficult to maintain the integrity ofany lining in fabricating and erecting a-complex piping system of any diameter.Alloy piping has an inherent technicaladvantage over lined or coated steel forany complex piping system.

The economics favor alloy piping overcarbon steel for complex piping systems(see Table 2), since labor to fabricate andinstall is 80-90% of the final cost. Thehigh proportion of labor in the overallcost strongly favors use of the best, notthe low-priced, material in complex pip-ing systems.

Alloy materials are affected somewhatdifferently by the position of the piping,Table 3. Horizontal lines that are slightlysloped and open vertical lines are easilyflushed out and drained completely. SShas suffered numerous failures when wa-ter residues have been left in horizontalruns that could not be completely drained.CA is somewhat more tolerant of suchwater residues, as is CS. However, bothperform best when easily drained. HA isless affected by pipe position.

Design velocities below 3 fps in fresh

- -- - ___ I -

By Arthur H. Tuthill, PE., Consultant to theNickel Development Institute

Cement-lined carbon steel piping is astandard material of construction for waterdistribution systems and the principal ma-terial found in most nuclear plant servicewater piping systems. Cement-lined car-bon steel was originally selected, appar-ently under the assumption that since itwas standard for municipal water handlingsystems it would be the most reasonablematerial to use for nuclear service watersystems.

Although this selection performed rea-sonably well initially, maintenance in-creased as the systems aged and the leakrate proved to be greater than could betolerated for nuclear service water pipingsystems.

Upgrading to alloy piping systems isunderway.

This report identifies some of the prin-cipal factors that affect the performance ofcooling water piping. Although severalfactors are interrelated, each is consideredseparately. This allows the engineer to usethis report as an engineering checklist toensure that none of the major factors havebeen overlooked. There is considerabledata in the published literature on each ofthe factors discussed but it has not beenbrought together as in this report.

In developing this report, carbon steelcement-lined piping and other coated steelpiping types are assigned the symbol(CS); 304L and 316L stainless steels arerepresented by (SS); C70600 and C61400by (CA); and 6% Mo and titanium by(HA). In some sections SS, CA and HAmaterials are grouped under the headingALLOY.

The factors that affect their behaviorare identified and one of three ratings is

given. A "G" rating indicates the pipingmaterial has given good performance un-der the indicated condition. "Y" indi-cates the material may give good perform-ance depending on site-specific conditionsand the interrelationship with other fac-tors. "R" means the material has notperformed well under the indicated condi-tions and special precautions are requiredif good performance is to be achieved.

Five design factors, three water qualityfactors, and six water composition factorsthat have a significant effect on the pipingmaterials are reviewed.

Design factorsDesign factors that influ-ence piping performanceinclude (1) size, (2) ar-rangement, (3) orientation,(4) velocity, and (5) fabri-cation.

It is difficult to cement-line or coat small-diameterpiping. It is even more dif-ficult to repair the lining orcoating where it has beendamaged by butt weldingduring pipe fabrication anderection or during inciden-tal maintenance. Alloy pip-ing has an inherent advan-tage over lined or coatedpiping in the smaller diam-eters (see Table 1).

Municipal water distribu-tion systems and utility rawwater intake systems wherecement-lined piping per-forms well are of large di-ameter, generally greaterthan 24 in., and more fre-quently 36 to 96 in. whereit is possible to repair lin-

Design factors

Table I. Pipe diameter - In.6 n. and < 8 n. - 30 in. > 30 n.

.t yl y 0

Table 2. ArrangementStraight runs Complex systems

CS 3 FtAlloy G G

Table 3. OrientationHorizontal Vertical

Level Sloped Open Dead ended

C. Y a G y

CA Y 3 G Y

SS Y G G YIR

HA Be 0 1 G

Table 4. Design velocity - FPSNo flow < 3 3-6 6-9 > 9

CS Y Y G Y ftC70600 A (A a Y

HA CA ( 0 (3 43,'C70600 is used rather than CA in this table as not all copper alloys are astolerant of the higher velocities.

or saline waters lead to excessive sedi-ment and debris buildup, biofouling andmicrobiological induced corrosion (MIC)in piping, Table 4. CS is more tolerant oflow velocity; however, it fouls readily andsediment buildup can lead to deteriorationof the coating. Corrosion failures of SSand under-sediment corrosion of copperalloy have occurred in low- and no-flowpiping.

The normal design velocity for pipingis about 6 fps and all of these pipingmaterials perform best at 6 fps. Actually,it is the low velocities where sediment candeposit and MIC can occur that must beguarded against. Generally, pipe designvelocities are well within the upper veloc-ity limit for these piping materials, al-though there are reports of cavitation fail-ures where too great a pressure drop hasbeen taken across a single orifice. SS andHA are unaffected by velocities higherthan normally found in piping systems.

Procurement practice and fabri-cability considerations have a major Waimpact on the suitability of each of -these candidate piping systems. Tat

In CS piping, the cement liningor coating is easly applied tostraight runs prior to pipe fabrica-tion and installation. After installa- CStion, the lining or coating is subject CAto mechanical damage when pumps Sand valves are removed for repair HAor replacement and when the sys- Tattem is opened and cleaned. Thelining is also subject to damagewhen, for example, a gusset might CSbe welded on to the outside to CAbrace the piping and reduce vibra- SStion. HA

The fact that so many cement-lined carbon steel piping systems Tathave been installed in nuclear ser-vice water piping systems indicates -that most of the problems can be CSovercome. That these apparently CAproperly installed carbon steel pip- SSing systems must now be upgraded HAdifferentiates the more stringent re-quirements that nuclear service water pip-ing systems must meet.

In CA systems copper nickel piping isroutinely fabricated into the complex pip-ing systems found in the engine rooms ofnaval and merchant ships. Fabrication isnot a limitation for CA provided brazingis limited to 2 in. and smaller diameters.

In SS systems Type 304L piping ispurchased to ASTM A 312 and fabricatedto user requirements. Fabrication is not alimitation for type 304L in fresh waterservice. However, other considerations,and the minimal differences in installedcost as compared to type 316L piping,tend to limit the use of type 304L piping.

Type 316L piping is also purchased toASTM A 312 and fabricated to user re-quirements. However, welding and post-welding cleanup is critical to success with316L. Type 316L tends to be used in the

2

more saline waters where 304L would notbe considered. Following are some of thekey considerations required to obtain thebest performance from 316L piping:1. Procure pipe to ASTM A 312.2. Fabricate pipe using matching compo-sition filler metal or higher Mo contentfiller metal for all butt and fillet welds.3. For butt welds specify smooth rootbead with no undercuts, no areas of in-complete penetration and no excessivebuildup of weld metal on the I.D.4. Specify HNO3-HF pickling of fabricat-ed piping before final assembly in thefield.5. Specify end protectors to prevent entryof dirt during shipment and storage afterpickling.

A major objective of pickling 316L isto improve the resistance of the welds tomicrobiological induced corrosion. It isquite possible that the use of a higher Mocontent filler metal such as 904L, 625 or

ter quality factors

)le 5. Cleanliness of waterDebris Bifoulh

Sediment sticks and musseClean Mud Sand stones barnac

Q G Y Y Y Rx G Y Y Y Qa Y G G RG 0 G G R

ble 6. Startup/standbyTime left full or in wet standby< 3days 4-7days > WI

O G G Yx G ~ ~ ~~~~Y A

G Y R(G 0 3

)le 7. Schedule for mechanical cleaningScheduled cleaning Interval

monthly/quarterly YeeG

X G FG0 G

and fillet welds.3. Specify smooth root bead with no un-dercuts, no areas of incomplete penetra-tion and no excessive buildup of weldmetal on the I.D.4. Specify HN03-HF pickling of fabricat-ed piping before final assembly in thefield.5. Specify end protectors to prevent entryof dirt during shipment and storage afterpickling.

For titanium:1. Procure pipe to ASTM B 337 Grade.2. Fabricate pipe in a qualified shop usingmatching composition filler metal for allbutt and fillet welds.3. Specify smooth root bead with no un-dercuts, no areas of incomplete penetra-tion and no excessive buildup of weldmetal on the .D.4. Specify end protectors to prevent entryof dirt during shipment and storage afterpickling.

5. Prohibit field welds, except inunusual situations when specialprecautions can be taken to avoidloss of shielding gas caused by out-

ers door breezes.Is,:1es Water quality factors

Water quality factors that affectpiping performance are cleanlinessof water, start-up/standby, andschedule for mechanical cleaning.

Design engineers tend to assumecooling waters are clean, a condi-

eek tion that exists only occasionally.In a few installations where specialcare is taken to operate and main-tain screens and filters diligently,plants have been able to maintainrelatively clean cooling water withconsiderable benefits in reducingcooling water system maintenance.

ily More often debris, (sticks, stonesand shells) and sediment (sand and

R mud) succeed in bypassing the sev-eral screening stations.

Debris and sediment are respon-sible for many of the problems the

nuclear industry has encountered with ser-vice water piping. The difference in be-havior of piping materials in clean andmore typical cooling waters is not fullyappreciated and frequently neglected inthe piping materials selection process.

All piping materials perform best in theclean waters designers assume will beused (See Table 5). Under-sediment cor-rosion is a common cause of corrosion ofstainless steel and copper alloy piping.The coatings used to protect carbon steelpiping also suffer progressive damagefrom sediment and debris. Debris can beeliminated by improved screens andstrainers. Sediment can be reduced bybetter piping arrangements, especially atthe intake. HA is quite resistant to debrisand sediment.

Biofouling is the most difficult factor tocontrol. Copper nickel's inherent resist-

C22 would also improve the resistance ofwelds in 316L to MIC. With a higheralloy filler metal the base metal shouldtend to protect the weld metal galvanical-ly, reducing the possibility of MIC attackon welds. The evaluations of the resist-ance to stagnant water conditions andMIC now underway should help clarifythe usefulness of such galvanic protectionof the weld metal and of HN03-HF pick-ling in improving the resistance of type316L to MIC and stagnant water corro-sion.

For HA systems, following are some ofthe key requirements needed to obtaingood performance from 6% Mo piping:1. Procure pipe to ASTM A 312(S31254), B 675 (N08637) or B 673(N08925).2. Fabricate pipe using higher Mo contentfiller metal, alloy 625 or C22, for all butt

Water composition factors

Table 8. ChloridesChlorides in ppm

< 200 < 1000 > 1000Cs a, Q --0_

304

Table 9. Dissolved oxygen/sulfides> 3-4 ppm 02 Demerated SUMf

Os 0 s

CA A

HA 0(Table 10. Chlorine residual

< 2 ppm 2-10ppm >-GA 0 A

HA ( _Table 11. pH ri

Normal 6-8

subject to rather high general corrosionrates and thinning. In deaerated waters oflow pH, copper alloys have excellent re-sistance to corrosion. SS and HA haveperformed well at pHs less than 5 andgreater than 9 (see Table 11).

The protective film forms readily oncopper alloys in warm waters, about 10minutes at 60 F, but takes much longer atthe lower temperatures encountered inarctic waters and in temperate waters dur-ing the winter months. The film formsalmost instantaneously on SS and HA inboth arctic and tropical waters. The per-formance of cement and most coatingsused with CS is not significantly affectedby temperatures within these ranges (seeTable 12).

Type 304 stainless steel tubing has suf-fered failures in fresh waters with appre-ciable manganese present (see Table 13).Copper alloy and higher alloyed tubingare less affected, although there are re-ports of corrosion of copper nickel insome waters with high manganese con-tent.

SummaryAlloy piping, not lined or coated carbonsteel, must be rated the material of choicefor nuclear service water piping systemsof less than 36 in. in diameter. The com-plexity of most nuclear water piping sys-

tems also favors alloy over carbon steel.Carbon steel cement-lined or coated is

most likely to meet nuclear service waterpiping reliability requirements in longstraight runs of 36 in. and larger diameters.

Copper nickel piping, although stan-dard in the complex piping systems char-acteristic of ships, has met with less suc-cess in nuclear service, due primarily tolow flow and under-sediment type corro-sion. Copper nickel may have to be re-evaluated if increasingly stringent regula-tions ban the use of biocides to controlbiofouling.

There is so little difference in finalinstalled cost that there appears to be onlya limited role for type 304L piping insome fresh water systems.

Type 316L piping has suffered MICand weld metal corrosion in nuclear ser-vice water piping. Pickling in HNO3-HFand the use of more highly alloyed weldmetal may increase the resistance of type316L piping to the point where it will beresistant to MIC and low flow conditionsin nuclear service water piping systems.Evaluations now underway should clarifythe usefulness of properly fabricated andpickled Type 316L piping.

6% Mo alloy piping is the materialmost likely to met the nuclear industry'sneed for highly reliable service water pip-ing.

Titanium also appears to meet the nu-clear industry's need for high reliabilitypiping provided field welds can be avoid-ed.

References1. Tuthill, A.H., "Successful Use of Carbon

Steel, Copper Base Alloys, and Stainless Steelsin Service Water Systems in Other Industries,"Proceedings EPRI Service Water System Reli-ability Improvement Seminar, Charlotte, N.C.,October 17-19, 1988.

2. Maurer, J.R. and G.J. Zelinski, "Devel-oping a Six Percent Molybdenum StainlessAlloy for Extended Service Water Piping Sys-tem Reliability," Proceedings EPRI ServiceWater System Reliability Improvement Semi-nar, Charlotte, N.C., October 17-19, 1988.

3. Tuthill, A.H., "Installed Cost of Corro-sion Resistant Piping," Chemical Engineering,March 3, 1986, p. 113.

THE AUTHOR

Arthur Tuthill is aconsultant to theNickel Develop-

o. ment Institute. Heholds a BS degreein chemical engi-neering from theUniversity of Vir-ginia and an MSdegree In metallur-

gical engineering from Carnegie Insti-tute of Technology. He is a registeredprofessional engineer in Louisiana.

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Temperature

Effect of temperature and hydrogen sulfide concentration on corrosion rate ofchromium-nickel austenitic stainless steels in hydrogen atmospheres at 75 to 500 psig(1.21-3.45 MPa). (Exposure time greater than 150 hr.)

40

Figure 10

Figure 1 0

Effect of Chromium in Normal Combustion Atmosphere (10)

C F

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2000

0

O 1000 -1800

0800

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CDEm 800Ea 1400

E 1200 _ Normal Combustion Atmosphere

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Chromium in Steel, %

Effect of chromium on the oxidation resistance of steel in a normal combustion atmosphere

Figure 11Stress Strain Curves for Type 304 and Type 301 (2)

MPa ksi140

120-800 -

100

00

C.)

600-

400 60

0 10 20 30 40 50 60 70

Engineering Strain, Percent

41

Figure 12

Effect of Cold Work onMechanical Propertiesof Type 202 (2)

Figure 14

Effect of Cold Work onMechanical Propertiesof Type 305 (2)

MPa

1400

ksi

- 200

1 200

1000 -

6 8000

us 6000

If-

c 40020

200

'Ea)

Q

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C0

C09U

Ea)

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LU

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00 20 40 60 0 20 40 60

Cold Work, percent

Figure 13

Effect of Cold Work onMechanical Propertiesof Type 301 (2)

Cold Work, percent

Figure 15

Effect of Cold Work onMechanical Propertiesof Type 310 (2)

MPa

1400

ksi

200

1200b

1 000 _

CS0)

a

-C)

'a0

800f-

600 _

400 _ 0I)L

.

M0

0w

200 -

00 20 40 60

Cold Work, percentCold Work, percent

42

Figure 16Effect of Cold Rolling and Test Directionon Notch Strength of Type 301 Sheet (2)

MPa ksi

240 Unnotched1600-Tesl

= 200 ~~~Strength

Figure 18

Izod Impact Values for Type 410Quenched from 1800 F (982 C) andTempered for 3 Hours at IndicatedTemperature (2)

Figure 19

Izod Data for 410 After Quenchingfrom 1800 F (982 C) and Temperingat 1150 F (621 C). (Bhn 228) (2)

J ft-lbJ ft-lb

160 r.120 - 160 120

100 I

120 I- 120 -

80k*0

0.0

:cJC1a)

80k- 60f- cmCjCLa

80 _

100

80

- 60

40

20

40H

401- 40 -

20

(I0 Fv I I I L I

D00 700 900 1100 1300

1 1 1 I i

OLF

I I I I I Iu . . .

-150 -100 -50 0 -50 100 150 200

1 1 1

250

l

C 300 500Tempering Temperature

700 C -100 -50 0

Testing Temperature

50 100

Figure 20

Fatigue Data for Quenched-and-Tempered Type 403(Rockwell C 24 to 26) (2)

ksi100

MPa Tested at Type 4037 F R, 24to 26

600 - (24 C)

80 SOO00F

Xo 400 _60 (260 C)

60-cj400

40-70F

200

0.01 0.1 1 10 100

Millions of Cycles to Failure

44

Figure 21Hot-Strength Characteristics (2)

MPa ksi

1400 200 - SemiausteniticPrecipitation and

..... \ Transformation-Hardening Steel

12001200 _ _ I~~~~~.... . .\.. ...

g 150 - 1000

C-

r 800

100

600 -

Martensitic and400 Ferritic Grades AusteniticGrades

50

200-

Low-CarbonUnalloyed Steel

0 aF 0 400 800 1200 1600

C 0 200 400 600 800Temperature

General comparison of the hot-strength characteristics of austenitic, martensitic andferritic stainless steels with those of low-carbon unalloyed steel and semi-austeniticprecipitation and transformation-hardening steels.

45

Figure 24, 25, 26

Comparative 100,000-hr Stress-Rupture Data for Types 316 and347 Tube and Pipe and on Type 304 Bar. (2)

MPa ksi

300F _ I Figure 24

L 'UI30

w 200U)

100

300

20

I ype 3u4Annealed Bar

I I I I I I I I I I

I

10

40

30 200 -

LaU)

0

Figure 25Type 321

Hot Workedand Annealed

Unexposed

Exposed for- 10,000 hrs. at

Test Temperature

I I I I I I I I I I

20

100

300

u 2000P,

10 I

40

30

Figure 26Type 347

Hot Workedand Annealed

20 _

100 _

10

I I I I I I I I

F 900 1000

C 500

1100 1200 1300 1400

I I I I

600

Temperature

700

48

Figure 27

Effect of Holding 10,000 Hr at 900, 1050and 1200 F (482, 566, and 649 C) on the ImpactCharacteristics of Type 410, 430 and 304 (11)

J ft-lb

60 F

60

40 F-

20 -

CnCc

c}

UC1

ut

E

zcC)0

C)

a.cEco

rs

80 F

60 -

40p

20 -

80 -

60 t-

40 -

20

I I I I II

C -150 -100 -50 0 50 100 150

Temperature

Hardness Values Were as FollowsDPN Hardness

After Exposure for 10,000 hr at

900 F 1050 F 1200 F(482 C) (566 C) (649 C)

410430304

125185138

125274140

124198147

123169141

49

Figure 28

Linear Thermal Expansion of the Three Main Classesof Stainless Steel

IN/FT0.24

7/

0.20 - AUSTENITIC 7GRADES 7 7

-j0.12

I-< 008

z

0.04-MARTENSITIC ANDFERRITIC GRADES

0 1 l

F 0 400 800 1200 1600 2(

C 0 200 400 600 800 1000

TEMPERATURE

0

1000

Figure 29

FactorsAffecting Heat Transfer (12)

Steam Side Water Film 18%o

Steam Side Fouling 8`0

Tube Wall 2 o

Water Side Fouling 330o

Water Side Film 39"o

50

Figure 30Overall Heat Transfer vs. Exposure Time (13)

8004450

3350 600

IL\

2250 _mo Type 304 Stainless Steel

1150 200 Arsenical Admiralty

_ ~~~~~ ~~ ~~~I I I I I I100 200 300 400 500 600

Exposure Time-Days

51

REFERENCES1. Steel Products Manual "Stainless

and Heat Resisting Steels' AmericanIron and Steel Institute, Washington, D.C.

2. Stainless Steel Industry Data.3. E. Pelitti, "Corrosion: Materials of

Construction for Fertilizer Plants andPhosphoric Acid Service:' Chemistry andTechnology of Fertilizers, AmericanChemical Society Monograph Series,Reinhold Publishing Corp. (1960), pp.576-632.

4. A.O. Fisher, "New Methods ofSimulating Corrosive Plant Conditions inthe Laboratory' Corrosion 17, (1961), pp.215t-221t.

5. Svetsaren English Edition 1-2; (1969),pp. 5.

6. G.C. Wood, Corrosion Science, 2(1962), pp. 173.

7. F. Eberle, F.G. Ely, and J.S. Dillon,"Experimental Superheater for Steam at2000 psi and 1250F. Progress ReportAfter 12,000 Hours of Operation," Trans-actions ASME, 76 (1954), pp. 665.

8. D. Caplan and M. Cohen, Corrosion,15 (1959), pp. 141t.

9. E.B. Backensto and J.W. Sjoberg,"Iso-corrosion Rate Curves for High-Temperature Hydrogen - HydrogenSulfide," Corrosion, 15 (1959), pp. 125t.

10. T.M. Krebs, Process Industry Corro-sion Notes, Ohio State University, Sep-tember (1960).

11. G.V. Smith, W.B. Seens, H.S. Linkand PR. Malenock, "MicrostructuralInstability of Steels for Elevated Tempera-ture Service," Proceedings ASTM 51(1951), pp. 895.

12. E.L. Lustenader and FW. Staub,"Development Contribution to CompactCondenser Design 'The InternationalNickel Company Power Conference, May1964 (Unpublished).

13. R.A. McAllister, D.H. Eastham, N.A.Dougharty and M. Hollier, "A Study ofScaling and Corrosion in CondenserTubes Exposed to River Water," Corro-sion, 17 (1961), pp. 579t-588t.

14. "C