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  1. 1. Characterization Study of Temper Embrittlement of Chromium-Molybdenum Steels API PUBLICATION 959 MAY 1982 American Petroleum Institute 1 11 2101 L Street, Northwest Washington, D.C. 20037COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  2. 2. A P I PUBLa959 8 2 M 0 7 3 2 2 9 0 0087Ll94 7 m Characterization Study of Temper Embrittlement of Chromium-Molybdenum Steels Refining Department API PUBLICATION 959 MAY 1982 American Petroleum InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  3. 3. __" A P I PUBL*757 8 2 H 0 7 3 2 2 7 0 0 0 8 7 4 7 5 7 i Nothing contained any API publication is be construed as granting any in to right, by implication or otherwise, for the manufacture, sale, or use in connection with any method, apparatus, or product covered by letters patent. This publication maybe used by anyone desiring to do so. The Institute hereby expressly disclaims any liability responsibility for loss or damage resulting from or its use;for theviolation of any federal, state, municipal regulation with which or an API publication many conflict; for the infringement of any patent resulting from or the use of an API publication, Every effort has been by the Institute to made assure the accuracy and reliability of the data presented. Copyright O 1982 American Petroleum InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  4. 4. API P U B L * 7 5 7 8 2 W 0732270 0087496 O W PmFACE At the October 1973 P Refining meeting, it was brought to the AI attention of the Committee on Refinery Equipment that 2-1/4Cr-1 Mo steel, an alloy frequently used to build hydrotreater reactors, was susceptible of to temper embrittlement. Reactors constructed this alloy could poten- loss of toughness. The embrittlement tially experience a considerable occurs partly during shop fabrication heat treatments, but more signifi- cantly, as a result operating in the embrittling temperature range. of Responding to this problem, CRE established a Task Group on Temper Embrittlement with members from the Subcommittees on Corrosion and on Pressure Vessels and Tanks.The task group was given two objectives: 1. To review the existing metallurgical data and research programs, and to recommend what approach should be taken to avoid embrittlement prob- lems with existing vessels. for 2. To recommend what further work was required to develop steels future pressure vessels which would be immune or less susceptible to temper embrittlement. On July 30, 1974, the API issued a cautionary letter prepared by the task groupto managers of all refineries in the United States and Canada. It alerted plant operators to the concern for in-service embrittlement of low alloy chrome-moly steels, and especially of 2-1/4Cr-1 Mo in thick sections. It also suggested precautions that should be taken to minimize the probability of brittle fracture inembrittled material. Earlier, at the May1974 Refining meeting, CRE accepted a task group proposal that P support a multiyear program to characterize the temper AI embrittlement susceptibility commercial plate, forging, and welds used of in reactors. The program would investigate the extent of embrittlement that might exist in operating vessels and how predict the embrit- to best tlement that could occur. In the spring of 1975, Westinghouse Research Corporation was selected as contractor for a 5-year characterization research program as outlined by the task group, with Dr. Shaw J. Bevil as principal investigator. A total of 64 samples, mostly 2-1/4Cr-1 Mo, but a few 1-1/4Cr-1 Mo and 3Cr-1 compositions, were provided by of Mo member companies, by steel suppliers, and by vessel fabricators. The 64 samples represented a large range of commercially produced steels, and included qualification welds, croppings from forgings, and nozzle and manway cutouts from plate ranging in thickness up to 6 inches. The characterization program was divided into Phases II. I and Phase I included a 64-sample study of the microstructure, grain size tensile properties, hardness, chemistry, including tramp elements, heat treatments, and toughness. Toughness data included determination of tran- sition temperatures before and after short time step-cool embrittlement heat treatment and of the shift in transition temperature resulting from the induced embrittlement.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  5. 5. For PhaseII, 25 heats were selected for additional embrittlement study. These heats were chosen to represent both the typical and the extremes in chemistry and in susceptibility to temper embrittlement as II was the measured by the step-cool test. The main thrust of Phase characterization of these alloys for embrittlement during isothermal exposure at five temperatures from F 950 F for times up 20,000 650 to to hours. These temperatures were chosen to span the range typical of service condit ions. The report which follows is a summary covering the Westinghouse characterization work and several ancillary studies, which developed during the nearly 6 years of work by the task group and Dr. Shaw. At the outset, the P program recognized that the characterization AI study could provide much needed. information about the temper embrittle- low ment- behavior of commercial alloy Cr-Mo steels used in reactors. It was not designed, however, probe the temper embrittlement mechanism. to Coincidentally, in late 1974, the Metals Properties Council Task Group on Tramp Elements in Pressure Vessel Steels was considering a proposal by Dr. C. J. McMahon, Jr., Department of Materials Science and Engineer- ing, University of Pennsylvania, to study the mechanism of temper em- brittlement, particularly with respect to the effect of tramp elements. The A I task group also reviewed the proposed program and conciuded that P it was a highly desirable supplement to the characterization study. As a result, P entered into an agreement with the Metals Properties AI Council for joint API/MPC support of McMahons three-phase, 5-year mechanism study. The primary objective was study, using laboratory to heats of controlled chemistry, the individual and synergistic embrittl- ing poeency of the elements manganese, phosphorus, silicon, antimony, and tin. A number of significant conclusions on the effects of these elements were derived from this study. Some of these data have been published in an article appearing in Vol. 102, of the Transactions 1980, ASME, Journal of Engineering Materials and Technology. Other supplement- ary papers are in process of publication, and a final report is now being prepared by Dr. McMahon. The AI Temper Embrittlement Characterization Study benefited P strongly from the support steel manufacturers and vessel fabricators. of Their representatives were active ex-officio members of the task group; their industrial backgrounds made their input to the program especially valuable. This is an outstanding example of the benefits derived to be from close cooperation between supplier and user. As a result of AI characterization study and the jointly supported P the API/MPC mechanism study, along with large individual research programs by some steel suppliers and vessel fabricators, which were at least partly stimulated by the API program, there is now a much better under- standing of the causes and implications of temper embrittlement for reactors built up about 1975. As a result the cooperative effort, to of it is now possible obtain hydrotreator reactors, both in the United toCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  6. 6. A P I PUBL*757 8 2 m 0732270 0087478 4 m Statesandabroad,withfargreaterinitialtoughnessandwithrelatively l i t t l e s u s c e p t i b i l i t yt ot e m p e re m b r i t t l e m e n t . It is w i t h a s t r o n gs e n s e of a c h i e v e m e n tt h a tt h et a s kg r o u ps u b m i t st h i s summary r e p o r t .R e a d e r s - are c a u t i o n e d t h a t t h e c o n c l u s i o n s i t draws are a p p l i c a b l e t o materials i nr e a c t o r sp r o d u c e d up t o a b o u t 1975. They are n o t a p p l i c a b l e t o t h e plate,forgings,andweld metal a v a i l a b l e t o d a y f r o m t h o s e m a n u f a c t u r e r s utilizing the necessary controls to produce material havinglowtemper e m b r i t t l e m e n ts u s c e p t i b i l i t y .F i n a l l y , i t s h o u l db er e c o g n i z e dt h a tt h e user has the responsibility to specify that material w i t h low e m b r i t t l e - ment s u s c e p t i b i l i t y i s r e q u i r e d , a n d t h a t i t cannotbeassumedthat all low a l l o y Cr-Mo material a v a i l a b l e t o d a y meets t h i s c r i t e r i o n . AI TASK GROUP ON TEMPER EMBRITTLEMENT F APRIL 1982COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  7. 7. CONTENTS Section Page III PHASE I: STEP-COOLED EMBRITTLEMENT EXPERIMENTS AND MATERIAL CHARACTERIZATION ...... o................. 7 IV PHASE II: ISOTHERMAL EMBRITTLEMENT EXPERIMENTS....o*o.. .**o14 VI1 PREDICTION OF LONG^ TERM ISOTHERMAL EMBRITTLEMENT. 19 X THE SEGREGATION OF ELEMENTS TO GRAIN BOUNDARIES I N Cr-Mo STEELS AFTER 20,000 EIR ISOTHERMAL EMBRITTLEMENT ASSESSED BY AUGER ~ALYSISo....oo.o............o..oo.oo.ooooooose.ooo25 XII A STUDY OF THE EFFECT OF HIGH PRESSURE HYDROGEN ON THE TEMPER EMBRITTLEMENT CHARACTERISTICS O &-MO F STEELS.ea.ooe.31COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  8. 8. " . A P I PUBL*757-82 W 0 7 3 2 2 3 0 0087500 9 W APPENDIX: DISCUSSION OF THE CHARPY TEST. ........................... A - l ........A-2 (a) Sources of Error in Charpy Impact Test Data (b) The Charpy Specimen Fracture Appearance ............A-1 Temperature Figures A l to A4 ......................................... A-6 (c) Experimental Scatter in the 40 ft-lb Transition ........................................... A-3 viii " " . ."COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  9. 9. A P I PUBL*759 8 2 m 0732270 0087501 O m CHARACTERIZATION STUDY OF TEMPER EMBRITTLEMENT OF CHROMIUM-MOLYRDENUM STEELS R . J. Shaw Westinghouse R&D Center P i t t s b u r g h ,P e n n s y l v a n i a1 5 2 3 5 AB S TRACT A c o m p r e h e n s i v ee v a l u a t i o no ft h es t e p - c o o l e da n di s o t h e r m a l embrittlementof Cr-Mo p r e s s u r e vessel steels (A387) h a sb e e nc a r r i e d o u t . The p r i m ep u r p o s eo ft h i sp r o j e c t was t oc h a r a c t e r i z et y p i c a l c o m m e r c i a lr e a c t o r s steels and weldments i n terms oftoughness and o t h e r p h y s i c a lp r o p e r t i e sp r i o rt ob e i n gp l a c e di n service and thechanges a n t i c - i p a t e di nt o u g h n e s sd u et ol o n g term service a t elevatedtempera- t u r e s .I nP h a s e I oftheprogram, 64 s u p p l i e d s t e e l s were c h a r a c t e r i z e d i n terms of t e n s i l e p r o p e r t i e s , m e t a l l o g r a p h i c f e a t u r e s and a n a l y t i c a l c h e m i s t r y .I nt h i sp h a s et h ec h a n g ei nt h et r a n s i t i o nt e m p e r a t u r ed u e t os t e p - c o o l e de m b r i t t l e m e n t was e v a l u a t e d from Charpy impact curves. I n Phase II, 25 s e l e c t e ds a m p l e s were i s o t h e r m a l l ye m b r i t t l e df o r 1,000, 10,000 and 20,000 hours a t 650, 725, 800, 875 and 9500F. S p e c i f i c r e l a t i o n s h i p sb e t w e e ns a m p l ec h e m i s t r y ,s t r e n g t hl e v e lo rs t r u c t u r e s were s t u d i e d . Based upon comparison Phase of I and II d a t a ,a na p p r o x i - mate r e l a t i o n s h i pb e t w e e nt h es t e p - c o o l e de m b r i t t l e m e n ta n dt h e i s o t h e r m a l m b r i t t l e m e n t i s derived. e This paper includes study the of repeatedde-embrittlement on two i s o t h e r m a l l ye m b r i t t l e d steels and t h e e f f e c t o fs t r e n g t h level and s t r u c t u r e on t h ei s o t h e r m a le m b r i t t l e m e n t of sample one of s t e e l . Subsidiary experiments performed Phase in I L of t h e program i n c l u d e t h e e f f e c t of highpressurehydrogen(3500psig) on temperembrittlement,fracturetoughnessmeasurements (JIc) on one samplefractographic valuation , e of i s o t h e r m a l l y m h r i t t l e d steels and e - a n Auger E l e c t r o n S p e c t r o s c o p i c e v a l u a t i o n o f g r a i n b o u n d a r y s e g r e g a t i o n of i s o t h e r m a l l ye m b r i t t l e ds a m p l e s . A s a r e s u l t of the API Temper EmbrittlementCommitteeefforts,theNationalBureauofStandardshas produced a s o l i ds t a n d a r d of 2-1/4Cr - 1Mo s t e e l (StandardReference Material 1 2 7 0 ) .S i n c et h ei n t e r p r e t a t i o no ft h ed a t ad e p e n d s upon t h e experimental s c a t t e r a na p p e n d i xh a sb e e nd e v o t e dt ot h ec h a r a c t e r i z a - t i o n oftheCharpyimpact t e s t procedure.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  10. 10. API P U B L * 7 5 7 8 2 W 0 7 3 2 2 9 0 0 0 8 7 5 0 2 2 KEY FOR ARBREVIATIONS AND SYMBOLS 40 f t - l b TT 40 f t - l b r a n s i t i o n e m p e r a t u r e l s o ( 4 0 ) T T a T FATT F r a c tA pe e a r aT r a n s i tT o m p e r a t u r e ur p nce i en (50% Shear) AT ( 4 0 ) h i f t S in 40 f t - l b TT Due t o Temper F m b r i t t l e m e n t AFATT S h iifnt FATT Due t o Temper F m b r i t t l e m e n t ATT T r a n S ieii f tp e r a t u r e i n ht m n s o T Subscriptsto FATT and 40 f t - l b TT U U n e m b r i t to e d lr as r e c e i v e d d i t i o n con ( i . e . d h go f e t ee re e m h r i t t l e m e n td e r i v e d from c o o l i n gt h r o u g ht h et e m p e r e m b r i t t l e m e n tr a n g eo ft e m p e r a t u r e sa f t e rt h ef i n a lh e a t treatment) D D e - e m h r i t tc e d d i t i o n lon - (1100oF, 2 h r s , water quench t o . remove a l l temper embrittlement) E S t e p - c o o l e d ic t ln d i t i o n embr t o e (see page 11) 1,000, 1 0 , 0 0 0 , s t a n df o rt h e number ofhoursofisothermalembrittlement 20,000 SM E Scanning Electron Microscope AES Auger E l e c t r o n S p e c t r o g r a p h IG Intergranular CL Cleavage DM Dimpled Rupture CB I Chicago Bridge Iron and JSW S tJ a p a n eel Works - WRDC Westinghouse R&D Center F OR Forging. PLA Plate SW A Submerged Arc Weld ESW Elec t r o s l a g Weld Material Key S A M S h i e l d e d Metal Arc Weld 1 1-1/4Cr - 1/2Mo 2 2-1/4Cr .- 1Mo 3 3Cr - 1Mo M S tM a rttu rn s i t i c ruc e e QBM Quenched M a r t e n s i t e -S t aun i t er e Rr i ctu B S t r u c t Br e n i t e u ai F -P F e r r i t e - PS t rru i tte r e ea l c u A FractureToughnessParameter Used i n A s s e s s i n g Low S t r e n g t h High D u c t i l i t y Metals J An E m b r i t t l e m e n tF a c t o r , (Mn + S i ) ( P + Sn) x l o 4 (WtX) - x A F m b r i t t l e m e n tF a c t o r , n (P + 4Sn f 5 A s + Sb) x lo-* (PP) X -? " -COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  11. 11. A P I PUBLr959 82 m 0732270 0087503 Characterization Study of Temper Embrittlement of Chromium-Molybdenum Steels I INTRODUCTION In 1975 t h e API awarded a c o n t r a c tt oW e s t i n g h o u s e R&D Center (WRDC) t oe v a l u a t et h et e m p e ra n b r i t t l e m e n tc h a r a c t e r i s t i c so f Cr-Mo p r e s s u r e vessel steels. The steels are d e s i g n a t e d A387 i nP a r t 4 of t h e A T Book ofStandards. SM Most of thesamplessupplied were of Grade .22(2-1/4Cr - 1Mo) and a fewsamplesofGrades 1 and 1 21 were a l s o included (1-1/4Cr - - 1/2Mo, 3Cr 1Mo). The 64 samples received r e p r e s e n t e d . a largerangeofcommerciallyprodpced steel i n c l u d i n g q u a l i f i c a t i o nw e l d si n1 - i n .a n d6 - i n .p l a t e ,l a r g en o z z l ec u t - o u t sa n d randomly shaped pieces of f o r g i n g and p l a t e material. These materials h a dr e c e i v e dh e a tt r e a t m e n tt y p i c a l of h y d r o - t r e a t e rr e a c t o rf a b r i c a - . t i o n . The samples were t y p i f i e d by a simplecode as f o l l o w s : FOR Forging PU Plate SW A Submerged Arc Weld EST4 E l e c t r o s l a g Weld S A M S h i e l d e d ?.letal Arc Meld 1 1-1/4Cr - 1/2Mo 2 2-1/4Cr - 1Mo 3 3Cr - 1Mo T h u s ,t h r o u g h o u tt h et e x t , 1 PLA means1-1/4Cr - 1/2Mo P l a t e material, 2 S W means A 2-1/4Cr - 1Mo Submerged Arc Weld material and so on. The o b j e c t i v e o f t h i s program was t o c h a r a c t e r i z e t y p i c a l com- mercial r e a c t o r s steels and weldments in terms oftoughness and o t h e r p h y s i c a lp r o p e r t i e sp r i o rt ob e i n gp l a c e di n service and thechanges a n t i c i p a t e di nt o u g h n e s s due t o long time s e r v i c e a t elevatedtempera- t u r e . It i s i m p o r t a n tt on o t et h a tt h e s e materials were t y p i c a lo f commercialproductionandfabrication up toabout1975, and are - not r e p r e s e n t a t i v eo ft h ep l a t e ,f o r g i n g s andweld metal, havinglowtemper e m b r i t t l e m e n ts u s c e p t i b i l i t ya v a i l a b l et o d a y [ I l . Phase I of t h e p r o j e c ti n c l u d e dt h em e t a l l o g r a p h ya n dg r a i ns i z e ,t h et e n s i l e p r o p e r t i e s and t h eR o c k w e l lH a r d n e s s e s ,t h ea n a l y t i c a lc h e m i s t r i e s includingthetrampelements,theheattreatmentsandCharpyimpact test d a t a . The latter y i e l d e dt h eF r a c t u r eA p p e a r a n c eT r a n s i t i o n Tempera- t u r e s (FATT) and t h e 40 f t - l bT r a n s i t i o nT e m p e r a t u r e s( 4 0f t - l b TT) f o r t h e steels i nt h eu n e m b r i t t l e da n ds t e p - c o o l e de m b r i t t l e dc o n d i t i o n . The terms AFATT and AT(40) r e f e r t o t h e c h a n g e i n FATT and t h e 40 f t - l b TT due t o temper e m b r i t t l e m e n t . 1 f .COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  12. 12. A P I PUBL*757 8 2 m 0732270 008750Ll b m The main p a r tPhase of i s o t h e r m a l m b r i t t l e m e n t of e 25 II was t h e r a c t e r i z a t io en cha steels a s s e s s e d n h a s e i P hof I. F i v e a i s o t h e r m a la n b r i t t l e m e n tt e m p e r a t u r e s were chosen a t 750F i n t e r v a l s from 6500 t o 9500F. Tests t om e a s u r et h e amount temper of embrittlement were c a r r i e do u ta f t e r1 , 0 0 0 ,1 0 , 0 0 0 and 20,000hours. A number of studies were also performed i n t h i s time.. These were: o The e f f e c to fr e p e a t e dd e - e m b r i t t l e m e n to ft h e steel. o The e f f e c t o fs t r e n g t h level and s t r u c t u r e . o Auger a n a l y s i so fg r a i nb o u n d a r i e so fe m b r i t t l e d steels. measurements. O JIC o E f f e c t ofhighpressurehydrogen on temperembrittlement. o I s o t h e r m a le m b r i t t l e m e n t of 1-1/4Cr. and 3Cr steels. By t h e endof1976 thefirstphase oftheprogramhadbeen completed. A t t h i sj u n c t u r ei nt h e program a number of discrepancies, b e t w e e nt h ed a t ag e n e r a t e d a t WRDC a n d o t h e r l a b o r a t o r i e s , were brought t ol i g h t . T h e s ei n c l u d e dt h ev i s u a lr e a d i n g so ft h ep e r c e n t a g eo f b r i t t l e f r a c t u r e on t h eC h a r p ys p e c i m e n s ,t h ec o n c l u s i o nt h a t AFATT was n o ta l w a y se q u a lt o AT(40), a b s o l u t e d i f f e r e n c e s i n t h e Charpyimpact e n e r g yc u r v e sa n dt h er e s u l t so ft h ea n a l y t i c a lc h e m i s t r i e s .I na d d i - t i o n , i t was found t h a ti nP h a s e I oftheprogram WRDC had used a Charpy specimenorientationwhich was d i f f e r e n t t h a n t h e Ö n e c o n v e n t i o n a l l y used by API. As a consequence, a number o fs u b s i d i a r ye x p e r i m e n t s were i n i t i a t e dt oc l a r i f yt h ev a r i o u si s s u e s .T h e s ei n c l u d e d a comparative Charpyimpact test s t u d yb e t w e e nJ a p a nS t e e l Works (JSW) and WRDC and a c o m p a r a t i v ef r a c t u r es u r f a c ee v a l u a t i o ns t u d yb e t w e e n Chicago-Bridge and I r o n ( C R & I ) and WRDC (see Appendix). A t t h e same time, s i n c et h e specimensforPhase II oftheprogram were machined i nt h ec o n v e n t i o n a l API o r i e n t a t i o n ,e x p e r i m e n t sd e s i g n e dt oe s t a b l i s ht h er e l a t i o n s h i p betweenthePhase I and Phase II o r i e n t a t i o n s were c a r r i e d o u t . Inaddition,the AI Task Group i n i t i a t e d a roundrobin P com- p a r a t i v ea n a l y s i so fs a m p l e s and a l s or e q u e s t e dt h eN a t i o n a lB u r e a uo f S t a n d a r d st oe s t a b l i s h a s o l i d 2-1/4Cr - 1Mo S t a n d a r df o rs p e c t r o g r a p h i c a n a l y s i s . A s a d i r e c t r e s u l t of the API Task Group e f f o r t s ,t h i ss t a n - d a r dd e s i g n a t e d S M 1270, i s now a v a i l a b l e f o r p u b l i c p u r c h a s e R from NBS. The s u b s i d i a r ye x p e r i m e n t s were c a r r i e do u td u r i n gP h a s e 1 of t h e 1 p r o j e c t which was concluded i n 1980. This paper reviews primary the r e s u l t s of t h e program.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  13. 13. A P I PUBL*757 8 2 W 0 7 3 2 2 7 0 0087505- 8 W II. GENERAL CONCLUSIONS Thispaperhasbeenorganized s o t h a tt h ev a l u e of t h ee x p e r i - mental r e s u l t s c a n b e a s s e s s e d a n d t h e n t h e i n f o r m a t i o n g e n e r a t e d h a s beenreviewed i n terms o ft h e s ec o n s i d e r a t i o n s . It c a nb eo b s e r v e dt h a t a small p o r t i o n of t h e s a m p l e s i n t h e u n e m b r i t t l e d (as r e c e i v e d )c o n d i t i o ne x h i b i t e dt r a n s i t i o nt e m p e r a t u r e s above normal ambient temperature (+50°F). Similarly, the number of s a m p l e se x h i b i t i n g TT a b o v en o r m a la m b i e n tt e m p e r a t u r es i g n i f i c a n t l y i n c r e a s e da f t e rs t e pc o o l i n go rl o n g - t i m ei s o t h e r m a le x p o s u r e .S i n c e thesamples were s e l e c t e dt ob et y p i c a lo fc o m m e r c i a lr e a c t o r materials, t h e s e r e s u l t s can be compared toreactorspriorto service ( u n e m b r i t t l e d s a m p l ec o n d i t i o n ) and a f t e rp r o l o n g e ds e r v i c e( s t e pc o o l e do r isothermally xposed ample ondition). ee igure e s c S F 44. I n t h e Appendix,"DiscussionoftheCharpy Test," i t was c o n c l u d e dt h a tt h eF r a c t u r eA p p e a r a n c eT r a n s i t i o nT e m p e r a t u r e (FATT) was a subjective measurement and was o p e nt oc o n s i d e r a b l ee r r o r .F o rt h i s r e a s o nm o s to ft h ed i s c u s s i o nh a sb e e nb a s e du p o nt h e 40 f t - l b T r a n s i - t i o nT e m p e r a t u r e ( 4 0 f t - l b TT) which i s r e l a t i v e l y n o n s u b j e c t i v e m e a s u r e m e n to ft h ee f f e c to ft e m p e r a t u r e . Even so, i t was f o u n dt h a t c o n s i d e r a b l e scatter c o u l d e x i s t i n t h e 40 f t - l b TT. A u n i v e r s a l i n d u s t r i a l problem i s t h e p r e d i c t i o n o f l o n g - t e r m ( u s u a l l yy e a r s ) service d e g r a d a t i o no f a material component. The u s u a l approach i s t o make p r e d i c t i o n s b a s e d upon c a r e f u l l y c o n s t r u c t e d s h o r t - term s c r e e n i n g tests. The c o n s t a n ti n e v i t a b l eq u e s t i o n i s "how w e l l do t h es c r e e n i n gm e t h o d o l o g i e sr e p r e s e n t - t h el o n g - t e r mc h a r a c t e r i s t i c s ? " The API program a d d r e s s e st h i sp r o b l e mf o rt e m p e re m b r i t t l e m e n tv e r y d i r e c t l y . In Phase I t h es h o r t - t e r ms c r e e n i n g t e s t f o rt e m p e re m b r i t t l e - ment ( t h es t e p - c o o l e de m b r i t t l e m e n tt e s t ) i s e v a l u a t e d and t h e n compared w i t hi s o t h e r m a le m b r i t t l e m e n td a t au pt o2 0 , 0 0 0h r .i nP h a s e II. Even though s i g n i f i c a n te x p e r i m e n t a l scatter e x i s t e d i n t h e d a t a , enoughexperiments were c a r r i e do u tt of o r m u l a t ea p p r o x i m a t e e x p r e s s i o n sr e l a t i n gt h ei s o t h e r m a le m b r i t t l e m e n tt ot h es t e p - c o o l e d e m b r i t t l e m e n t . The r e s u l t sg e n e r a t e d from t h ed a t ab a s eo ft h i s program a p p e a rt o show t h a tt h es t e p - c o o l e de m b r i t t l e m e n tc a nb er e l a t e dt ot h e I s o t h e r m a le m b r i t t l e m e n tb u t i s n o te q u a lt ot h ev e r yl o n g - t e r m embrittlement of a s t e e l . In f a c tt h es t e p - c o o l e de m b r i t t l e m e n ta p p e a r s t oc o r r e l a t ew i t h 250-hr. isothermal embrittlement a t 875F. However t h es t e p - c o o l e de m b r i t t l e m e n ts c r e e n i n g t e s t shouldnotbereplacedwith 250-hr. i s o t h e r m a le m b r i t t l e m e n tw i t h o u tf u r t h e re x p e r i m e n t st oc o n f i r m 3COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  14. 14. the prediction from Equation4 ) , page 21. This equation is primarily ( for 2 1/4 Cr 1 Mo steels. The equation, developed from the complete AT 0 ) data set, suggests that the 30-year in-service embrittlement, ( 4or 3 40 ft-lb TT is equal to times the step-cooled ft-lb Transition Temperature shift. Attempts to correlate the composition of a steel to the observed embrittlement indicated too many variables were present to formulate a reasonable regression analysis with the (statistically) disorganized i21 data available. The correlation with the often employed “J-factor” viz. (Mn + Si) (P + Sn) x 104 was relatively poor for data from weld metal, plate and forgings- Figures 4 (a) and (b). However, this cor- relation is not intended for weld metal and the correlation for plate and forging (black points) is comparable with that of similar studiesi31 Some of the scatter in the data for the plate and forging may indicate that the steel processing procedure is an important variable in the A387 Class 22 steel. The resultsof the PhaseII isothermal embrittlement tests may be summarized as follows: (1) 800- The maximum isothermal embrittlement occurred in the 9 50°F range. (2) Embrittling susceptibility varied widely in the 25 samples. Some reached peak embrittlement at 800°F or 875OF after 20,000 hr. exposure, while some had apparently not reached maximum embrittlement after 20,000 hr. at 950OF. (3) A possibility of embrittlement was found half of the in 65O0F. samples isothermally embrittled at (4) After 20,000 hr. exposure, the extremes and average values of the 40 ft-lb Transition Temperature for the 1 /2 Cr - 1 4 Mo samples were as follows: Exposure Average 40 foot-pound Range of40 foot-pound Transition Temperature Transition Temperature (OF) Temperature (OF) ( O F ) -___. - Min’ .~ MaxJ’ 650 - 11 - 115 + 55 725 - 8 - 100 + 60 8170 + 22 - 75 + 100 875 + 34 - 75 + 140 950 + 24 - 55 + 100 J. n Minimum and Maximum values are not for the same sample but of illustrate the range transition temperatures observed.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  15. 15. A P I PUBL*757 8 2 m 0732270 0087507 (5) Of t h et w e n t yt h r e e 2 1 / 4 C r , one 1 C r and one 3Cr samples i s o t h e r m a l l ya g e d , a t o t a l of twelve s a m p l e se x h i b i t e d a 40 ft-lbtransitiontemperaturehigherthan 500F - which i s f r e q u e n t l yu s e dt ot y p i f yt h ea m b i e n tt e m p e r a t u r e - a t one o r moreof t h e 5 agingtemperatures,andforoneormoreof t h e 3 aging times. The breakdown by materials type and alloytype is giveninTable 29(a) and ( b ) . (6) Even t h o u g h h e a t a a s e t d b i s small, i t s u g g e s t ss t r o n g l y t h a t 2 1 / 4 C r weld metal h a s a - h i g h e r s u s c e p t i b i l i t y t o t e m p e re m b r i t t l e m e n tt h a np l a t eo rf o r g i n g s - Table29(b). (7)Because of t h e small d a t ab a s e , no f i r mc o n c l u s i o nc a nb e drawn a b o u tt h ei s o t h e r m a le m b r i t t l e m e n t of 1 C r and 3Cr a l l o y s , b u t i t would appearweld metal o fb o t ha l l o y sh a v e some s u s c e p t i b i l i t yt oe m b r i t t l e m e n t . In g e n e r a l ,t h eu p p e rs h e l fi m p a c te n e r g y ,w h i c hr e f l e c t st h e toughnessofthe s t e e l , was not s i g n i f i c a n t l y changed from the u n e m b r i t t l e dc o n d i t i o nt oe i t h e rt h es t e pc o o l e de m b r i t t l e m e n to rt h e i s o t h e r m a l l ye m b r i t t l e dc o n d i t i o n . The e f f e c t ofrepeatedde-embrittlement a t llOOOF f o r 2 h r s . on 8750F i s o t h e r m a le m b r i t t l e m e n t( i nf u l l yp o s t weld h e a tt r e a t e ds p e c i - mens) showed t h a t t h e d e - e m b r i t t l e d c o n d i t i o n was approximately a con- s t a n t . It was concluded temper that embrittlement i s r e v e r s i b l ea n d t h a tt h ee m b r i t t l e m e n t i s due t od i f f u s i o no ft h et r a m pe l e m e n t s . The e f f e c t of s t r e n g t h l e v e l and s t r u c t u r e was r e a s o n a b l y c l e a r . The q u e n c h e d b a i n i t e - m a r t e n s i t e ) ( and tempered s t e e l had lower t r a n s i t i o nt e m p e r a t u r e st h a nt h es l o w - c o o l e d( f e r r i t e - p e a r l i t e ) s t e e l on the ingle omposition ested. s c t However, a f t e r 20,000-hr. isothermal e m b r i t t l e m e n t a t 875OF thequenchedandtempered s t e e l had e m b r i t t l e d t o the- same l e v e l as theslow-cooled s t e e l whichhadde-embrittled s l i g h t l y . The u n t e m p e r e d h i g h t r e n g t h ) ( s steel, which does not r e p r e s e n tt h et y p i c a ls t r e n g t h l e v e l s of FWHT steels e x c e p t p o s s i b l y i n t h eh e a ta f f e c t e dz o n e , had v e r y h i g h i n i t i a l t r a n s i t i o n t e m p e r a t u r e s b u td e - e m b r i t t l e ds u b s t a n t i a l l ya f t e r2 0 , 0 0 0 - h r . a t 8750F. The e f f e c t ofhighpressurehydrogen(3,500psig) a t 8750F a f t e r 1,000 h r . was mostpronounced inthe.ferrite-pearlitesamplewhich was degraded to hydrogen due the exposure. Bainite samples the in same a u t o c l a v ed i dn o t show a r a d i c a l c h a n g e i n t h e i r p r o p e r t i e s . The Auger E l e c t r o nS p e c t r o s c o p i c (AES), a n a l y s e so ft h ee m b r i t t l e d g r a i nb o u n d a r i e s showed h i g hc o n c e n t r a t i o n so ft h ee m b r i t t l i n ge l e m e n t P and t o a much lesser e x t e n t Sn. I n t e r e s t i n g l y , steels w i t hh i g h c o n t e n t so f A s d i dn o t reveal s e g r e g a t i o no ft h i se l e m e n t .T h i s i n f o r m a t i o ns u p p o r t st h e formof t h ee m b r i t t l e m e n tf a c t o r X = (1OP 5% + + 4Sn + A s ) proposed Bruscato. by [ h l The most s u r p r i s i n gc o n c l u s i o nCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  16. 16. API P U B L * 7 5 7 8 2 W 0 7 3 2 2 7 0 0 0 8 7 5 0 8 3 m fromthe AES s t u d y was t h a t Cu s e g r e g a t e st ot h eg r a i nb o u n d a r i e s .T h i s e f f e c t i s notnormallyfound and t h e r o l e of Cu a t t h eg r a i nb o u n d a r i e s i s f a r from clear. Overall, t h i s programhasservedtoidentifytheprimarytemper e m b r i t t l e m e n t c h a r a c t e r i s t i c s of t h e c o m e r c i a l Cr-Mo p r e s s u r e vessel steels u s e df o rv e s s e lc o n s t r u c t i o n up t oa b o u t 1975. General guide- l i n e s o ft h e material d e g r a d a t i o n f o r i n d u s t r i a l a p p l i c a t i o n s h a v e b e e n deduced. 6 ___COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  17. 17. API PUBLm757 8 2 W 0 7 3 2 2 7 0 0087507 5 W III. PHASE I: STEP-COOLED EMBRITTLEMENT EXPERIMENTS AND MATERIAL CHARACTERIZATION P r i m a r yO b i e c t i v e sf o rP h a s e I Phase I r e p r e s e n t e d t h e p r i m a r y c h a r a c t e r i z a t i o n o f t h e s u p p l i e d s t e e l samples. The c h a r a c t e r i z a t i o nc o n s i s t e d of ( iM e t a l l o g r a p h i s t r u c t u r e ) c (ii) AST" g r a i ns i z e (iii) Rockwell B Hardness ( i vT e n s i l p r o p e r t i e s ) e (a) O. 2% y i e l d s t r e n g t h (b) Ultimate t e n s i l e t r e n g t h s (c) R e d u c t i o nn i area (cl) Elongation ( v )A n a l y t i c a lc h e m i s t r yw h i c hc o n s i s t so fa n a l y s e sf o r C, Cr, Mo, Mn, S i , N i , Cu, P, S , Sn, Sb, O, N, A s . (vi) The g e n e r a t i o n of Charpyimpactcurvesofunembrittledand step-cooledtemperembrittledsamplesyielding ( a ) FATTU; 40 f t - l b TTU ( b ) FATTE; 40 f t - l b TTE ( c ) AFATT ( o r amount of e m b r i t t l e m e n t , FATTU - FATTE) ( d ) AT(40) ( o re m b r i t t l e m e n tj u d g e d by s h i f t i n 40 f t - l b t r a n s i t i o nt e m p e r a t u r e ) . Material Kev The s a m p l e s l i s t e d a c c o r d i n g t o t h e material key are as f o l l o w s : ( see page 1) 7COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  18. 18. A P I PUBL*759 8 2 m 0 7 3 2 2 7 0 00875LO L W ~~ ~ ~~ ~ ~ Material Key Sample Number ___- 1 PLA 2, 0, 2, 0 5 5 6 2 PLA 1, 7 ,1 2 ,1 3 ,1 4 ,3 3 ,3 6 ,4 5 ,4 6 ,4 7 , 48, 4, 5, 0, 1, 2, 4, 5 5 5 7 7 7 7 7 3 PLA 64 1 FOR 77 2 FOR 9 , 1 0 , 1 5 ,5 6 ,5 7 ,5 8 ,5 9 ,7 8 3 FOR 61 1 SAW 4 2 SAW 1 8 ,1 9 ,2 0 ,2 1 ,2 2 ,2 3 ,2 4 ,2 5 ,3 4 , 353738394041 , , , , , 3 SAW 65 2 ESW 8., 1 6 2 6 2 7 7 6 , , , 2 SMA 63, 7, 8, 9 6 6 6 3 SMA 66 Metallography M e t a l l o g r a p h i cs e c t i o n s were prepared from eachsampleand e t c h e d so as t o show t h e p r i o r a u s t e n i t i c g r a i n s i z e and s t r u c t u r e . Photographs were t a k e n a t X200 and X500, two t y p i c a le x a m p l e s are shown i nF i g u r e s 1 and 2. The s t r u c t u r e of each sample i s l i s t e di nT a b l e 1. ASTM G r a i nS i z e( T a b l e 1) The ASTM g r a i n s i z e was judgedbycomparisonwithstandard chartseitherdirectly on t h e m i c r o s c o p e o r bycomparisonwiththe photographs. The e r r o ri nt h e s ed e t e r m i n a t i o n s i s about +1 i n ASTM g r a i n s i z e (ASTM E112-74 P l a t e 1). 8 . " ;""-COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  19. 19. A P I PUBLU757 82 m 0 7 3 2 2 7 0 0087511 3 m T e n s i l eP r o p e r t i e s( T a b l e 1) The t e n s i l e p r o p e r t i e s were judgedfromonetensile. test oneach sample. the In forged and p l a t e material t h et e n s i l es p e c i m e n s were s t a n d a r d 0.505 inches diameter gauge as shown i nF i g u r e 3 , t y p e 1 . The l o n g i t u d i n a l axes ofthesespecimens were p a r a l l e l t o t h e r o l l i n g d i r e c - t i o ni nt h ep l a t e .T r a n s v e r s et e n s i l es a m p l e s were taken from t h e weldments. A s t a n d a r dt e n s i l ec o u l dn o tb et a k e n from most of t h e weld s a m p l e sw i t h o u ti n c l u d i n gt h eh e a ta f f e c t e dz o n e (HAZ) w i t h i nt h eg a u g e l e n g t h .S i n c et h eb a s ep l a t eo r HAZ c o u l dp o s s i b l yy i e l dp r i o rt ot h e weld material, i t was decidedtousereducedsizesampleswhichincluded only weld metal w i t h i nt h eg a u g el e n g t h .T h u s ,t h et e n s i l ed a t ap r o - ducedforweldsamples r e l a t e s s o l e l y t o t h e w e l d .S i n c et h eg r a i ns i z e i s s u f f i c i e n t l y small i ne a c hs a m p l e ,g r a i ns i z ee f f e c t s on t h e t e n s i l e p r o p e r t i e ss h o u l db en e g l i g i b l e .( T h ee f f e c to fg r a i ns i z e on t e n s i l e p r o p e r t i e s i s o n l ya p p a r e n ti ft h e r e are less thanabout 5 g r a i n s i n a c r o s ss e c t i o n ) . A diagramofthetensilesamplesused i s g i v e ni n F i g u r e 3. The s i z e o ft h e weld t e n s i l es a m p l e s i s as f o l l o w s : ___ Tensile SpecimenType Sample No. from Fig. 36 4 3 8 3 16 3 34 4 35 3 37 3 38 4 39 3 40 3 41 3 42 3 43 3 44 3 67 2 68 2 69 2 76 2 -COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  20. 20. A P I PUBLm959 8 2 3 2 2 7 0 8 7 5 3 2 07 00 5 Rockwell B hardnessmeasurements were a l s o t a k e n on eachsample(Table 1). A n a l y t i c a lC h e m i s t r y( T a b l e 2) The a n a l y t i c a l c h e m i s t r y was donebythefollowingtechniques: C LECO - Combustion - I R D e t e c t i o n S ( I R Infra-Red) O LECO - HighTemperature Fusion Thermal - Conductometric N (LECO i s a t r a d e name) Cr M o E S ii s sSo n c t r o m e t e r m i pe Cu Ni M n P As Phosphor-Molybdate Technique Sn Sb The l a t t e r fourtrampelements were e v a l u a t e d a t WestinghouseResearch Center and t h e rest were e v a l u a t e d a t Lukens S t e e lR e s e a r c h . It s h o u l db en o t e dt h a tt h et a b l e sg i v et h r e es i g n i f i c a n t f i g u r e s ,w h e r e a si nf a c t ,t h ee r r o ri nm o s t i s s u c ht h a t only two s i g n i f i c a n t f i g u r e s are warranted. S p e c i f i c a l l yt h ec l a i m e dp r e c i s i o n i s as f o l l o w s ( p p means partspermillion): Element C S 2 .002% k Precision 3 ppm FIl ” . E l emen t Cu Ni - i- .01% L- Precision .01% ~____ O N Cr -I 5 ppm ? 3 ppm i- .05% iIl Mn As Sb +- .01% F 10% i- 5% Mo i- .08% Sn 2 5% Si F .01% 1 P 4 5 ppm o r b e t t e r 10 .COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  21. 21. A P I PUBL*757 8 2 M 0 7 3 2 2 7 0 O Ö B 7 5 1 3 7 W Also i t s h o u l db en o t e dt h a tt h ea n a l y s e sf o rs a m p l e s 1 2 , 13 and 1 4 showed a s i g n i f i c a n t v a r i a t i o n i n M as f o l l o w s : n S amp l e M ( s i t e A) n M ( s i t e B) n 12 .67 .42 13 .,59 .39 14 .53 37 Thequotedvalues of M i n t h e t a b l e s n are theaverageoftheabove estimates: CharpyImpact Data ( T a b l e 3 ) The d a t a g e n e r a t e d f o r t h i s r e p o r t stemmed from two s o u r c e s : (1) WestinghouseResearch on S a m p l e sn o th i t h e r t oe v a l u a t e da n d ( 2 ) samples evaluated a t t h ev a r i o u ss u p p l i e r s l a b o r a t o r i e s . In o r d e r t or e d u c et h et o t a ls c o p e and expense of t h ep r o g r a m ,t h ed a t as u p p l i e d b yv a r i o u ss o u r c e s was a c c e p t e da n dt h er e m a i n i n gd a t ag e n e r a t e d at Westinghouse Research Centér. Since standard the step-cooled emhrittle- menttreatment,termedthe SOCAL step-cooledembrittlement,hasbeen used i n t h e API i n d u s t r y , v i z : 1100°F - 1 h r Cool a t 10°F/hr 1000°F - 1 5 h r Cool a t 10"F/hr 975°F - 24 h r Cool a t 10"F/hr 925°F - 60 h r Cool a t 5"F/hr 865°F - 100 h r Cool a t 5 0 " F / htro 600°F - a i r c o o l T h i se m b r i t t l e m e n tt r e a t m e n t was u s e dt h r o u g h o u tt h e series. D i s c u s s i o n ofPhase I Data A a t t e m p tt of i ta ne q u a t i o nt ot h ed a t ag e n e r a t e di nP h a s e n I was c a r r i e do u tu s i n gr e g r e s s i o na n a l y s i st e c h n i q u e s .U n f o r t u n a t e l y , t h e d i s t r i b u t i o n of e l e m e n t s ,g r a i ns i z e s and s t r e n g t h l e v e l s among t h e set was s u c ht h a t no s p e c i f i cm a j o rt r e n do rc o e f f i c i e n t sa s s o c i a t e dCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  22. 22. w i t he a c hv a r i a b l ec o u l db ef o u n d . At f i r s ts i g h tt h i s is surprising, s i n c et h e r ea p p e a r st ob e a s u f f i c i e n tr a n g eo fe a c hv a r i a b l ew i t h i nt h e number samples of taken. However, a s t a t i s t i c a l l yd e s i g n e de x p e r i m e n t f o r 14 e l e m e n t sp l u sg r a i ns i z e and s t r e n g t h , i.e. 16 v a r i a b l e s would r e q u i r ec o n s i d e r a b l y more t h a nt h e 6 5s a m p l e sa v a i l a b l e .M o r e o v e r ,t h e v a r i a b l e s would b ea r r a n g e da c c o r d i n gt ot h ed e s i g nr a t h e rt h a nt a k e n at random. Consequently, i t was n o tp o s s i b l et of i n d a f i t t e de q u a t i o nt o thePhase I d a t a f o r two r e a s o n s , v i z . i n s u f f i c i e n t d a t a and u n f o r t u n a t e o r g a n i z a t i o n of t h ev a r i a b l e s . The c o r r e l a t i o nb e t w e e nt h eo f t e n employed "J-factor and AT ( 4 0 ) , shown i n Fig. 4 ( a ) , i s r e l a t i v e l yp o o r forbothplate andweld metal. The datacan,however,beexpressedintheformofthehisto- grams and a few u s e f u lo b s e r v a t i o n s made. The histograms are shown i n F i g u r e s 5 through 18. The u p p e rh i s t o g r a mi ne a c ho ft h e s ef i g u r e s r e p r e s e n t s a l l t h e weld and p l a t e and forgedsamples,whereastheweld metal c o n t r i b u t i o n a l o n e i s r e p r e s e n t e d by t h eh a t c h e d areas w i t h i n t h e t o t a lh i s t o g r a m . The dashed curves are a na p p r o x i m a t i o nt ot h es h a p eo f t h eh i s t o g r a mf o rt h ep l a t e a n df o r g e ds a m p l e sa n ds i m i l a r l yt h es o l i d c u r v er e p r e s e n t st h ew e l d s .T h u s , a comparison of weld and p l a t ep l u s forgedsamplecharacteristicscanbe made withineachhistogram. There i s a q u e s t i o n of how well t h eh i s t o g r a m sr e p r e s e n tt h e Cr-Mo A387 s t e e l s . The samples were drawn from many s o u r c e s , some of which were from a c t u a l p r e s s u r e v e s s e l s and o t h e r s from h e a t s o r weld- mentsproducedtosimulatethenormalvessel steels. A few of t h e samples were includedintheprogrambecausethey were " i n t e r e s t i n g " i n t h a t t h e y hadanomalouslyhightemperembrittlementfractureappearance t r a n s i t i o nt e m p e r a t u r e ( F A T T ~ ) o rr e p r e s e n t e d some extreme i n composi- tion.Thesesamplesmightput a b i a s on theaccumulateddataandhence i nt h i sr e s p e c tt h eh i s t o g r a m s may n o t t r u l y r e p r e s e n t t h e class of s t e e l . However, t h e r e are s u f f i c i e n t a m p l e s h a t h e i s t o g r a m s h o u l d s t t h s g i v e a r e a s o n a b l ea p p r o x i m a t i o nt ot h en o r m a lc h a r a c t e r i s t i c s . F i g u r e s 5, 6 and 7 show t h e FATT d a t a . The FATTU ( u n e m b r i t t l e d ) and FATTE ( e m b r i t t l e d ) show t h a t as a class t h e weld have a h i g h e r FATT t h a nt h ep l a t ea n df o r g i n g s .B o t h FATTE and AFATT, due t o temper e m b r i t t l e m e n t ,r e v e a lt h a tc e r t a i n 2 1 / 4 C - 1Mo submerged arc weld- r ments (2 SAW) h a v ep o o r e re m b r i t t l e m e n tc h a r a c t e r i s t i c st h a nt h e rest. Overall,onecanconcludethatweld may bemorepronetoembrittlement and may have a h i g h e r u n e m b r i t t l e d FATTU t h a n t h e p l a t e andforged material. F i g u r e s 8 through 1 7 show t h e d i s t r i b u t i o n o f mostof t h e ele- m e n t si nt h e s t e e l s . F i g u r e s 8, 9 and 10 show s i g n i f i c a n td i f f e r e n c e s between weld the metal and p l a t e a n df o r g i n g sf o r C , M and S i . n In g e n e r a l ,h i g h e rl e v e l s of M and S i l e a dt oh i g h e r n FATT v a l u e s i n t h e presence of P. [4,5,61COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  23. 23. A P I PUBL*759 8 2 m 0732270 087515 0 O m P, With regard to the tramp elements, Sn, As and Sb, Figures 11 through 1 4 , little difference is found between weld metal and plate for P and As, whereas plate and forgings exhibit a higher content of Sn and Sb. A secondary high peak in is associated with2 SAW samples. This P again confirms the secondary-highAFATT peak in Figure 7 for 2 SAW materials. (See page 8 for sample numbers) The histogram for does not indicate a specific trend, whereas S the histograms for and O, Figures 16 and 17, show very much higher N It concentrations of these elements for the welds. is interesting to (ESW) samples exhibit the lowest oxygen note that the electroslag weld on temper content of the weld class. The role of these two elements embrittlement is not known. The J embrittlement factor(Mn + Si) x (P + Sn) x lo4 does not show a strong difference between plate and weld metal, even though it is not intended to be used for welds. Interestingly, the ESW samples all fall in the 50-100 range. If they were taken out of the weld set, then the weld metal would show a greater population to 250 compared 200 at with 100 to 150 for the plate and forgings (Figure18). Even though the histograms show reasonable correlations between the FATT data and compositions, especially Si and P and C, any Mn, interpretation of the trends must be treated with caution. Simple plots of FATT~, FATT~or FATT versus - of the compositional elements or one any the J embrittlement factor show specific trend whatsoever. This no observation only confirms the fact that the expression for FATT in terms of composition is a complex function which represents the multiple interactions of the primary alloying elements and the tramp elements.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  24. 24. API P U B L * 7 5 7 8 2 W 0 7 3 2 2 9 0 0087516 2 W IV. PHASE II: ISOTHERMAL EMBRITTLEMENT EXPERIMENTS The p r i m a r yo b j e c t i v ei nP h a s e II was t o c h a r a c t e r i z e t h e i s o - thermalembrittlementof 25 s e l e c t e d steels and t ou l t i m a t e l yc o m p a r e t h i sd a t aw i t ht h es t e p - c o o l e de m b r i t t l e m e n t data of Phase I. The i s o t h e r m a le m b r i t t l e m e n tm a t r i x was as f o l l o w s : Temperature (OF) Time ( h r ) [E] 950 x I 11,000 10,000 20,000 The samples were s e l e c t e d on t h eb a s i so f i) Material a v a i l a b i l i t y i i ) Extremes i n t e p - c o o l e d m b r i t t l e m e n t s e i i i ) Extremes i n o m p o s i t i o n a e l e m e n t s c l iv) tructure S and s t r e n g t h l e v e l The p r i m a r yd a t ag a t h e r e d was t h e 40 f t - l b TT and FATT. Wherever p o s s i b l ea ni n d i c a t i o no ft h eu p p e rs h e l fv a l u e was a l s oo b t a i n e d . The b a s i cd a t ag a t h e r e d i s g i v e ni nT a b l e s 4 through12. F i g u r e s 19 through 43 show t h e 40 f t - l b TT and FATT p l o t t e d as a f u n c t i o n of t h e isothg.rpa-X..embrittlementtemperaturefor 1,000, 10,000 and 20,000 h r . For r g f e r e z i e ,t h ëu n e m b r i t t l e d (U) and step-cooled e m b r i t t l e d ( E ) t r a n s i t i o n . t e m p e r a t u r e s are i n d i c a t e d bybenchmarks in t h e same figures. Samples tested with- Phase II o r i e n t a t i o n are i n d i - c a t e dw i t ha na s t e r i s ki nT a b l e 3. F u r t h e rd a t a i s g i v e ni nT a b l e1 6 where t h ee f f e c t o fs p e c i m e no r i e n t a t - i o n i s shown. The s u p p l i e dd a t a f o r sample 26 (Table 3 ) was p r o b a b l y i n c q r r e c t and thebenchmark U r e p r e s e n t sa ni n d e p e n d e n t test. Where T and E d a t af o rt h eP h a s e I II s p e c i m e no r i e n t a t i o n were n o ta v a i l a b l e ,P h a s e I d a t aa d j u s t e da c c o r d i n g t ot h er e l a t i o n s h i pg i v e ni nS e c t i o n V I below were used. F o rt h es a m p l e sw h i c he x h i b i td i s t i n c te m b r i t t l e m e n t( o r i n c r e a s ei nt h et r a n s i t i o nt e m p e r a t u r e ) ,t h e maximum e f f e c t i s i n t h e r a n g e 8000F t o 9500F. (See igures F 19 t o 4 3 ) Histograms of t h e 40 f t - l b TT i nt h eu n e m b r i t t l e d and s t e p - c o o l e de m b r i t t l e dc o n d i t i o n s are compared w i t h t h e maximum embrittlernentCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  25. 25. A P I PUBLa957 A2 W 0 7 3 2 2 9 0 0 0 8 7 5 1 7 W after 1,000 and 20,000 hr isothermal embrittlement in Fig. 4 4 . These histograms give a clear indication of the general trend of embrittlement after long term isothermal exposure.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services ,
  26. 26. V. THE EFFECT OF DE-EMBRITTLEMENT Samplesreceivedfromvarioussources had r e c e i v e d a number of d i f f e r e n th e a tt r e a t m e n t si n c l u d i n g a r a n g e of p o s t - w e l dh e a tt r e a t m e n t s (PWHT) . InPhase I thesesamples were t e s t e di nt h e" a s - r e c e i v e d " c o n d i t i o nw h i c h was t e r m e dt h e" u n e m b r i t t l e d "c o n d i t i o n . The F r a c t u r e A p p e a r a n c eT r a n s i t i o nT e m p e r a t u r ef o rt h i sc o n d i t i o n was a b b r e v i a t e dt o FATTU, w h e r et h es u b s c r i p t U d e s i g n a t e s" u n e m b r i t t l e d . "I nf a c t , due t o t h e slow c o o l i n gt h r o u g ht h et e m p e re m b r i t t l e r n e n tr a n g e ,v a r i o u sd e g r e e s oftemperembrittlementmight well havebeenexperienced by each sample i nt h i sc o n d i t i o n . The same samples were s u b j e c t e dt ot h e SOCAJ, Step- Cooled Temper F m b r i t t l e m e n tt r e a t m e n ta n dg i v e nt h ed e s i g n a t i o n E. (See Page 11) It was t h o u g h tt h a tt h ep o s s i b l ec o r r e l a t i o n sb e t w e e ns a m p l e c h a r a c t e r i s t i c s( s t r u c t u r e ,y i e l ds t r e n g t h and composition) and t h e degreeoftemperembrittlement wouldbe b e t t e r r e v e a l e d by comparisonof t h e E c o n d i t i o nw i t hs a m p l e si n a d e - e m b r i t t l e dc o n d i t i o n .S a m p l e s were d e - e m b r i t t l e d by h e a t t r e a t i n g a t llOOoF f o r 2 h r and water quenching. T h i sc o n d i t i o n i s g i v e nt h ed e s i g n a t i o n D. Thus, - a number of samples h a v eb e e nt e s t e di nt h r e ec o n d i t i o n s . U - Unknown degreeofembrittlementoras-received E - Step-cooledembrittlement from c o n d i t i o n U D - D e - e m b r i t t l e dc o n d i t i o nf r o mc o n d i t i o n U In Phase I, AFATT was d e f i n e d as F A T T E - ~ ~a~ ~ sU m i l a r l y t h e nd i change i n t h e 40 f t - l b TT was AT(40) = T ( 4 0 ) E - T(40)~- The d a t a fromPhase I a n dt h ec u r r e n t t e s t s are g i v e n i n T a b l e s 13, 14 15. and S i n c et h e U c o n d i t i o nm i g h tb es l i g h t l yt e m p e re m b r i t t l e d ,o n e shouldexpectthe FATTU and T ( 4 0 ) ~ t o b e g r e a t e r t h a n FATTD and T ( 4 0 ) ~ and less t h a n PATTE a n dT ( 4 0 ) ~ ,r e s p e c t i v e l y .I n s p e c t i o n of T a b l e s 13 and 14 shows t h a t i n g e n e r a l t h i s i s n o tt h e case. I n o r d e r t o e x p l o r et h er e a s o nf o rt h e many d i s c r e p a n c i e s i n t h e d a t a ,t h ec u r v e s of t h e D, U and E c o n d i t i o n were compared. I nn e a r l y e v e r yi n s t a n c e ,t h eu p p e rs h e l f of D > U > E as i s alsoobviousfrom Table PS. Thus on e m b r i t t l e m e n tt h ec u r v e s are d e f i n i t e l y changed i n t h eu p p e rs h e l fo r 100% d u c t i l er e g i o n . Also t h eg r a d i e n to ft h eC h a r p y c u r v e s becomes less s t e e pw i t he m b r i t t l e m e n t .COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  27. 27. A P I PUBL*757 82 W 0732270 087519 0 B m Data similar t ot h ea b o v e was found f o r 3.5Ni-Cr-Mo-V rotor s t e e l by D r . J. Watanabe. L61 He p o i n t e d u t h a t n t e r g r a n u l a r o i f r a c t u r ee x t e n d st ol o w e rt e m p e r a t u r e s as thedegreeoftemper embrittlementncreased. i It i s r e a s o n a b l et os u g g e s tt h a tt h e i n t r o d u c t i o no fa ne x t r a mode o f f r a c t u r e , i.e., i n t e r g r a n u l a rf r a c t u r e by temperemhrittlement, serves a l s ot oc h a n g et h eg r a d i e n t so ft h e Charpy curves. A. S. Tetelman and A. J. McEvily, Jr. r71 p o i n to u tt h a t t h e Charpycurvegradient is difficulttodefine anddependsstronglyon m i c r o s t r u c t u r a lv a r i a b l e s . They s t a t e t h a t i n g e n e r a l a processwhich l o w e r st h eu p p e rs h e l fv a l u e w i l l t e n dt ob r o a d e no u tt h e 100% d - u c t i l e - t o - b r i t t l er a n g e( o rc h a n g et h e Charpycurveslopeto a l o w e rg r a d i e n t ) . It f o l l o w s from t h i ss t u d yt h a tt h er e l a t i o n s h i pb e t w e e nt h e (D) and (U) c o n d i t i o n i s f a r from simple.Consequently a c l a r i f i c a t i o n of t h ea m b i g u i t yi nt h ed a t ac a u s e d by v a r i a b l e d e g r e e s o f e m b r i t t l e m e n t stemming from a r a n g eo fc o o l i n g rates i s n o t p o s s i b l e .COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services

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