The Effect of Testing Procedure on Implant Test Results

Transcription

1 The Effect f Testing Prcedure n Implant Test Results Crrelatin is fund between implant test results and micrhardness when assessing the hydrgenassisted cracking f micrallyed HSLA pipe steels BY A. J. BRYHAN ABSTRACT. Hydrgenassisted cracking (HAC) susceptibility f micrallyed HSLA pipe steels was evaluated using the implant test perfrmed with several parameters. Crrelatins between HAC susceptibility and carse grained heataffected zne (HAZ) micrhardness, ally cntent and fur published carbn equivalent equatins were statistically examined. It was fund that nne f the carbn equivalent equatins crrelated with either implant r micrhardness test results. Hwever, implant test results (critical stress) and micrhardness did crrelate. N crrelatin was fund between implant test results and cmpsitin. The measured critical stress depended n the test prcedures used, althugh the relative HAC susceptibility ranking was fund t be independent f these prcedures. Implant test cnditins that were relatively mre severe than thse in use at mst labratries were fund t be advantageus. Intrductin The implant test (Ref. ) is frequently used t evaluate the hydrgenassisted cracking susceptibility f steels. In this test, a ntched bar is incrprated int a weldment in such a way that the temperature at the rt f the ntch is raised almst t the fusin pint. During the prcess, hydrgen is intrduced int the weldment frm the cellulsic electrde used fr welding. Subsequent lading f the test bar simulates weld restraint and causes delayed cracking t ccur if the applied stress is abve sme critical value characteristic f the test cnditins and steel. Delayed cracking apparently results due t hydrgenassisted prpagatin f cracks initiated at the rt f the ntch. A relatively high cracking susceptibility is dented by a lw critical stress. This means that, using the shielded metal arc prcess, welding f the steel wuld be difficult and may require special techniques, such as preheating, t reduce cracking tendency. Fr the past few years Climax has evaluated the weldability f several candidate highstrength il and gas pipeline steels using the implant test. The results f this test prvide a relative ranking f susceptibility t hydrgenassisted cracking, (HAC) but nt an abslute measure. Fr the results f the implant test t be useful in predicting the ease f field welding, a number f different steels must be evaluated in the labratry and in the field, and any future steels then cmpared t the previus critical stress data. The critical stress is the applied stress belw which specimen failure will nt ccur in minutes (min). The critical stress is cmmnly nrmalized by dividing it by the ultimate tensile stress f the steel being evaluated. This is the published CS/UTS rati. In additin t the critical stress, it is usual practice fr the maximum heataffected zne (HAZ) micrhardness t be determined fr each steel; this number may be useful fr predicting HAC susceptibility. It is generally anticipated that the steel becmes less resistant t hydrgenassisted cracking as the micrhardness increases. Paper presented at the 6st AWS Annual Meeting held in Ls Angeles, Califrnia, during April 48, 98. A. J. BRYHAN is a Senir Research Assciate, Climax Mlybdenum Cmpany t Michigan, Ann Arbr, Michigan. Bth the CS/UTS and maximum HAZ micrhardness are units that must be actually measured fr the steel f interest. This requires sme equipment, time and expense. An attractive methd fr predicting HAC susceptibility wuld be t have a crrelatin between weldability and cmpsitin. T this end, scalled carbn equivalent equatins have been derived. Thrugh the years, a number f carbn equivalent equatins have been tried; in fact, fr higher carbn levels, a certain amunt f predictin f weldability is pssible. Hwever, as shwn belw, when attempting t apply current carbn equivalent equatins t mdern lw carbn highstrength lw ally (HSLA) pipe steels, the ability t predict relative freedm frm cracking becmes less precise. This prblem became apparent when the authr attempted t crrelate implant test results with fur f the mre cmmnly used carbn equivalent equatins. The equatins used were the IIW equatin, (Ref. 2) which is the standard used mst frequently by Western cuntries, the It Bessy equatin (Ref. 3) that is used mst frequently by the Japanese, the Duren equatin (Ref. 4) develped at Mannesmann in Germany, and the Tanaka equatin (Ref. ), again frm Japan. The last tw equatins are nt cited in the literature as frequently as the first tw, but were included with the hpe that they might ffer refinements t difficulties encuntered when using the first tw equatins. The fur equatins are shwn in Table. As may be seen, all f the equatins are linear with nly additive rather than multiplicative terms. T attempt t reslve the difficulty f relating experimental results t WELDING RESEARCH SUPPLEME NT 69s

2 Table Carbn Equivalent Equatins IIW carbn equivalent equatin (Ref. 2): Mn Cr + M + V CE = C Ni + Cu ItBessy carbn equivalent equatin (Ref. 3): Mn Cr + Cu Si V PM = C M Ni + + E 6 Duren carbn equivalent equatin (Ref. 4): Si Mn + Cu Cr Ni CE = C M V 4 Tanaka carbn equivalent equatin (Ref. ): Si + Cu 4 M Mn Cr P N, B = C these equatins, a statistical analysis f all previus Climax implant test data was perfrmed. The gal was t learn hw the ttal cllectin f data wuld crrelate, hping t relate critical stress r maximum HAZ micrhardness t cmpsitin using ne f the abve equatins, r else t derive a new equatin. When difficulties were encuntered, additinal implant tests were perfrmed t try t duplicate the results used by thers in deriving these carbn equivalent equatins. The gal was t learn whether mdifying test parameters wuld prvide test results that wuld crrelate with ne r mre f the existing predictin equatins. Experimental Prcedures Multiple linear regressin analysis was perfrmed using as accumulated data base f Climax implant test results n HSLA steels. The cmpsitin f the steels, the critical stress, critical stress/ultimate tensile strength rati, and maximum HAZ micrhardness are shwn in Table 2. Typical welding parameters used fr the implant test are presented in Table 3. The statistical analysis first examined fr crrelatins between the dependent variables CS, CS/UTS and maximum HAZ micrhardness and the independent cmpsitinal variables C, Mn, P, S, Si, Cu, Ni, Cr, M, Nb, V, and Al. Then, several empirical equatins invlving the elements in linear, quadratic and crssprduct terms were frmulated and tested fr fit t the dependent variable data using multiple linear regressin techniques. Finally, the crrelatins between the labratry data and the fur published carbn equivalent frmulas were examined. As nted abve and discussed further belw, this statistical analysis shwed HAC susceptibility t be inde Table 3Typical Welding Parameters fr the Implant Test Perfrmed by the Climax Research Labratry Prcess: shielded metal arc welding (SMAW) Vltage: 2832 V Current: A Travel speed: 4.7 mm/s ( ipm) Average heat input: 986 kj/m (2 kj/ in.) Preheat: Nne Ambient temperature: 23 C (73 F) Electrde: Lincln Shield Arc X7, E 8 G, 4 mm (/32 in.) diameter Implant test schedule: Re/a five time, min 2 6 Actin Weld depsited. Weld surface cled in water t rm temperature. Specimen remved frm water. Specimen laded in test fixture, testing cmmences. Test ends fr specimens that did nt break. pendent f cmpsitin fr the lw carbn HSLA steels studied. This finding prmpted an investigatin f the rle f varying the implant test prcedures. The implant test may be perfrmed several different ways. ur prcedure has been t cut samples frm the steel f interest frm midplate thickness s that the specimen axis is transverse t the rlling direc Table 2Cmpsitin, Critical Stress (CS), Rati f Critical Stress t Ultimate Tensile Stress (CS/UTS), and Maximum HeatAffected Zne Micrhardness (HV) fr HSLA LinePipe Steels Evaluated at Climax c Mn P S Si Cmp sitin, wt% Cu Ni Cr M Nb Al V CS/UTS Test results CS HV s I SEPTEMBER 98

3 Table 4Experimental Prcedures fr Implant Tests Implant test step Climax methd IIW methd Japanese methd Implant specimen gemetry Remval f implant blank Supprting plate Lad applicatin Welding heat input Diameter Ntch cnfiguratin Ntch depth Ntch rt radius Specimen axis rientatin Psitin in thickness Temperature when lading begins Lad hlding time.6 mm Helical ntch, angle 6 deg.46 mm.8.4 mm Midthickness CMn mild steel Rm temperature Minimum 6 h kj/cm 6, preferably 8 mm Circular ntch, maximum angle 4 deg, if pssible 4 deg. mm. mm Rlling directin Midthickness, T/4 if greater than 2 mm Similar cmpsitin r CMn mild steel Between and C Minimum 6 h 7 k /cm 8 mm Circular ntch, angle 4 deg. mm. mm Rlling directin Midthickness Same steel C Minimum 48 h 7 kj/cm tin. The sample blank is then machined t frm a cylindrical rd.6 mm (.22 in.) in diameter and 7 mm (2.2 in.) lng. A helical ntch is carefully machined at ne end with a rt radius f.8.4 mm (.3. in.). The machined specimen is inserted int a flat ungrved 4. mm (.7 in.) thick mild steel plate abut 2 mm ( in.) square. A manually applied welding pass is then made ver the specimen using a mving guide t cntrl travel speed t within apprximately an 8% range. Typical heat input is abut kj/cm (2 kj/in.). The welded surface f the implant test assembly is inverted int rm temperature water exactly 2 min after welding and left in the water fr 4 min. An additinal 4 min are allwed fr installatin in the testing machine and cmmencement f lading. The sample is at rm temperature when it is laded t sme predetermined nminal stress. Depending upn whether r nt the specimen breaks within min, anther implant specimen is prepared and tested at a higher r lwer stress. The greatest stress that can be sustained withut failure in min is designated the critical stress. Table 4 cmpares ur prcedure t tw thers that are cmmnly used: that specified by the Internatinal Institute f Welding (IIW) and the methd cmmnly reprted in Japanese literature. The differences f greatest significance are ntch acuity, specimen temperature at the time f lading and welding heat input. T investigate the effects f varying these parameters, implant tests were perfrmed n six steels using different cmbinatins f parameters:. Specimen rientatin relative t the rlling directin, transverse r parallel. 2. Ntch radii f.8.4 mm (.3. in.) r. mm (.4 in.). 3. Welding heat input kj/cm (2 kj/in.) r 7 kj/cm (43 kj/in.). 4. Specimen temperature at the time f lad applicatin f either rm temperature r C (3 F). All samples were.6 mm (.22 in.) in diameter and were helically rather than circumferentially ntched. The helical ntch assures that the mst critical regin f the HAZ and the ntch will intersect; this is mandatry fr an accurate test. The cmpsitins f the six candidate linepipe steels used in this investigatin f test prcedures are shwn in Table. Five f the six steels were als used in the initial statistical analysis. All steels have the capability f meeting strength requirements fr API X7 grade pipe depending n prcessing and wall thickness. Steels D and F have smewhat mre ally than the ther fur steels and apprximately % higher ultimate tensile strength, and wuld prbably be cnsidered structural rather than pipe steels. Results Using the data fr the 2 steels in Table 2, n crrelatin was fund between the measured HAC susceptibility and ally cntent that wuld permit the predictin f hydrgenassisted cracking susceptibility frm cmpsitin. A fair crrelatin between maximum HAZ micrhardness and critical stress and CS/UTS rati was fund (see Figs. and 2). Hwever, this relatinship is nt especially suitable fr weldability predictin. The matrix f crrelatin cefficients fr the measures f HAC susceptibility (CS, CS/UTS, and HV) and cmpsitin is shwn in Table 6. The crrelatin cefficients are indicative f the scatter f ne variable abut anther. Squaring the crrelatin cefficient (R 2 ) gives a quantity called the cefficient f determinatin. If ne variable is related t anther with an R value f. (R =.), then a plt f the tw variables, ne against the ther, wuld be a line with n scatter. Table Cmpsitin f the LinePipe Steels and Electrde Used fr Implant Tests t Determine the Effect f Implant Test Parameters, Wt% Steel identificatin C Mn Si P S Al Cr M Nb Ni Cu N V A B C D E F Welding electrde _ WELDING RESEARCH SUPPLEMENT I 7s

4 [ T r 9 8 7, ^ 3 HARDNESS, HV 3\ Fig. Critical stress vs. maximum HAZ micrhardness, R =.S7 \ HARDNESS, HV Fig. 2CS/UTS vs. maximum HAZ micrhardness, R =.82 Table 6Crrelatin Cefficients Implant Test Results vs. Cmpsitin c Mn P S Si Crrelatin Cefficient (R) Value Cu Ni Cr M Nb Al V HV CS/UTS 7 CS.336 HV.4 Implant Test Results vs. Carbn Equivalent Equatins CS/UTS CS HV IIW It Bessy Duren Tanaka The sign f the crrelatin cefficient reflects the trend f the data plt (R is negative if the variables are inversely related). As the amunt f data scatter increases, R 2 becmes less than.. If, fr example, R =.8 (R 2 =.64), then it may be said that 64 percent f the variance f the dependent variable can be explained by the assumed functinal relatinship between the tw variables. A value f R 2 clse t zer suggests that there is nt much linear crrelatin between the tw variables, while a value clse t. cnntes a strng linear relatinship. Fr example, the highest degree f crrelatin reprted in Table 6 is fr CS as a functin f HV; fr this relatinship R =.8, which means that CS decreases as HV increases and 66% (.8 squared) f the variance f CS can be explained by the hardness f the heataffected zne. As shwn in Table 6, nne f the cmpsitin variables had a statistically significant crrelatin with any f the measures f HAC susceptibility. (Graphical examples f the amunt f data scatter fr varius crrelatin cefficient values are shwn in Figs. 4.) In additin t the pr crrelatin f the dependent variables CS, CS/ UTS, and HV with individual cmpsitin variables, attempts t generate a new carbn equivalent equatin using multiple linear regressin f the data shwed similar pr crrelatins. Fr all the empirical equatins prpsed and tested by the authr, the multiple crrelatin cefficients were extremely lw. Fr this reasn, nne f the equatins is presented. Als shwn in Table 6 is the matrix f crrelatin cefficients btained fr CS, CS/UTS and maximum HAZ micrhardness f ur implant test data against the fur published carbn equivalent equatins. Nne f the fur Table 7Attempted Curve Fitting Equatins Used T Relate Published Carbn Equivalent Equatins t Experimental Data y A + B X CE CE/ (A X CE + B) A X EXP (B X CE) A X CE B A + B x LG (CE) A x EXP (B/CE) A + B/CE / (A + B X CE) dependent variable; CS, CS/UTS r maximum HAZ micrhardness CE = numerical value btained frm applicable published carbn equivalent equatin carbn equivalent equatins crrelated with the results f the implant tests. The inability f the carbn equivalent frmulas t predict measures f HAC susceptibility is illustrated graphically in Figs. 34, which are reprductins f cmputer plts f the CS, CS/UTS and maximum HAZ micrhardness against these fur equatins. The scatter in the data is evident. Als shwn n each f Figs. 34 is a curve that is the result f attempting t fit the dependent variables CS, CS/ UTS and maximum HAZ micrhardness t an equatin using ne f the carbn equivalent frmulas as an independent variable. In each case the curve presented is the best fit (greatest crrelatin cefficient) available using equatins f the frm shwn in Table 7. The R value shwn in Figs. 34 represents the data scatter abut the cmputergenerated line that best fits the data. Since the line shwn in Figs. 34 is nt neccessarily straight, the R value frm Table 6 (linear analysis) may be different than the value shwn in the figures. Nne f the equatins is a gd predictr f the actual experimental data. Many reprts are available in the literature that discuss relating the implant test results t cmpsitin in a manner similar t that attempted here. Several f these papers are listed in the 72s I SEPTEMBER 98

5 CARBN EQUIVALENT, CE C G Fig. 3Experimental maximum HAZ hardness vs. the IIW carbn equivalent equatin R = , CARBN EQUIVALENT, CE? Fig 4Experimental maximum HAZ hardness vs. the ItBessy carbn equivalent equatin, R =.47 I / CARBN EQUIVALENT, CE3 Fig. Experimental maximum HAZ hardness vs. the Duren carbn equivalent equatin, R = ^ / F / / ' / 22 I I CARBN EQUIVALENT, CE4 Fig. 6 Experimental maximum HAZ hardness vs. the Tanaka carbn equivalent equatin, R = ' 3 Z r \ ^s i ' i i r CARBN EQUIVALENT, CE Q r I _%L_ Fig. 7Experimental critical stress vs. IIW carbn equivalent in eauatin 2, Table 7, R =.77 ; \ \ \,. NT \ I I CARBN EQUIVALENT, CE2 Fig. 8Experimental critical stress vs. ItBessy carbn equivalent in equatin 8, Table 7, R =.423 bibligraphy (Refs. 28). These papers reprt success in relating cmpsitin t sme weldability parameter. The authr was nt able t accmplish this. As mentined previusly, additinal implant testing was perfrmed trying t duplicate the results btained by thers and t learn hw variatins in prcedures wuld affect test results. The results f this series f implant tests are shwn in Table 8 and Fig.. The riginal hypthesis was that, by changing the testing prcedures frm thse used by us t thse used elsewhere, the relative tanking f steels wuld be changed and a better crrelatin with published carbn equivalent frmulas wuld be fund. It is necessary fr the ranking f the steels t change and nt just the numerical value f critical stress in rder t btain a better crrelatin between implant test results and any f the published carbn equivalent equatins. As may be seen in Fig., the ranking f the steels by the implant test was virtually cnstant fr the varying cmbinatins f testing cnditins, with the numerical critical stress value being directly prprtinal t test severity. ur prcedure, (cnditin 3) is the mst severe cmbinatin f parameters and prduced the numerically lwest critical stress values. Because the ranking f the steels was nt significantly changed when ging frm ur usual prcedure t thse WELDING RESEARCH SUPPLEMENT I 73s

6 2 > LU Q. c < CARSN EQUIVALENT, CE3 Fig. 9Experimental critical stress vs. Duren carbn equivalent in equatin 8, Table 7, R =.44 \ \ \_ 'H ^ \ ^ ^ ^ CARBN EUIVALENT, CE4 Fig. ~Fxperimental critical stress vs. Tanaka carbn equivalent in enuatin 8, Table 7, R =.499 _ I, I I \ Na CD C ^, ~~~~ CARBN EQUIVALENT, CE Fig. 77Experimental CS/UTS vs. IIW carbn equivalent in equatin 2, Table 7, R = a.7.6 U.b.a.3.2. : ) \p.2 ^^^^ CARBN EQUIVALENT, CE2 Fig. 2Experimental CS/UTS vs. ItBessy carbn equivalent in equatin 8, Table 7, R = CARBN EQUIVALENT, CE3 Fig. 3Experimental CS/UTS vs. Duren carbn equivalent in equatin 8, Table 7, R = p uj.8 >.7 p.6. g.4 S.3.2 ' \ \ c \ ^ _ ^ ^. ' CARBN EQUIVALENT. CE4 Fig. 4Experimental CS/UTS vs. Tanaka carbn equivalent in equatin 8, Table 7, R =.3 used by thers, the results btained in the statistical analysis are independent f testing parameters. Thus, the lack f crrelatin between ur implant test results and the published carbn equivalent equatins is nt related t testing methd. Table 9 cmpares the implant test ranking, carbn equivalent value fr each equatin, and maximum carsegrained HAZ micrhardness fr the tw welding heat inputs. The steels are ranked accrding t hydrgenassisted cracking susceptibility as measured by the implant test. It is again bvius that nne f the published carbn equivalent equatins ffers the ability t predict the ranking f the steels in the implant test. Similarly, they cannt predict the ranking accrding t micrhardness. An interesting pint t nte, hwever, is that implant test ranking and hardness crrelated fairly well. This supprts the accepted belief that cracking susceptibility is directly prprtinal t hardness. Discussin The idea f being able t predict hw easily a steel will weld based upn cmpsitin is very attractive since it wuld greatly facilitate materials selectin. It wuld permit steels t be ranked s that thse with a certain value wuld be acceptable and thse with anther value wuld nt. This, in fact, is what is frequently requested in materials specificatins fr steels. 74sl SEPTEMBER 98

7 In the past, befre the advent f micrallying and cntrlled rlling, adjusting the carbn cntent r majr allying elements in a steel was the cmmn methd f btaining increased strength. Increasing the carbn cntent increased strength; unfrtunately, hwever, it als increased the susceptibility t hydrgenassisted cracking. This is where the carbn equivalent equatins became valuable, fr with relatively large ally additins the prperties f a weld culd be predicted based upn cmpsitin. The present steels used fr highstrength pipe rely upn a balanced cmbinatin f relatively small and cntrlled additins f selected elements and thermmechanical treatment (Ref. 9). N knwn carbn equivalent equatin can accurately reflect the subtle cmpsitinal differences between these steels. This becmes especially true when the cmpsitinal differences between steels are small. It may be that this is the primary reasn why n knwn carbn equivalent equatin can yet crrelate with either implant test results r micrhardness fr HSLA linepipe steels. The carbn equivalent equatins TEST CNDITIN ] 2 J 6 e. D <> v NTCH ACUITY (mm) ~T FT.8.. TEMPERATURE AT LADING ( HEAT INPUT (kj/mm)..7.. A B C D E STEEL IDENTIFICATIN Fig. The change in critical stress due t varying the testing cnditins were riginally derived frm test results fr steels f widely varying cmpsitin. The cmpsitin f mdern HSLA pipe steels is fcused int a narrw range, hwever, and the equatins cannt reslve the small differences in steels. The inability f the authr t find a new carbn equivalent equatin relating relative cracking susceptibility r micrhardness t cmpsitin amng the steels listed in Table 2 is, fr the present, attributed t the data base being bth t small and cntaining insufficient systematic variatin f the cmpsitin. Because f the discrepancy between experimental test results and thse predicted by the carbn equivalent equatins, it is recmmended that future use f these equatins be fr infrmatinal purpses nly and that the resistance t HAC be measured directly. It shuld be pinted ut that the IIW equatin, which is mst frequently cited in the Western wrld, is bviusly inapprpriate fr predicting hydrgenassisted cracking fr steels f the type studied here, as shwn in Table 8Critical Stress Values btained Using Several Test Cnditins Steel identificatin A B D E F rientatin Lngitudinal Lngitudinal Lgitudinal (74) 469 (68) (74) 29 (42) 276 (4) 276 (4) 22 (32) 68 (24) 6 (23) (92) 24 (76) 6 (87) 49 (7) 469 (68) 379 () 3 (4) 234 (34) 268 (39) Critical St ess by Test Cnditin, MPa (ksi) (69) 34 () 22 (32) 248 (36) 282 (4) 2 (22) 2 (22) () 386 (6) 79 (84) 63 (89) 4 (79) 3 (73) 86 (8) 393 (7) 4 (8) 27 (4) 24 (3) () 6 (93) 6 (87) 62 (9) 73 (82) (74) 32 (< ) 33 (44) (72) 8 79 (84) 66 (88) Test C nditin Temperat Heat Ntch acuity (mm) ure at lading ( C) input (kj/mm) Table 9Cmparisn f Implant Tests btained Using Several Test Cnditins A B C D E F Critical stress ranking by test cnditin shwr belw separately ~ IIW Test cnditin Carbn ec uivalent Steel identificatin It Bessy Duren Tanaka Micrha rdness, HV..7 kj/mn ~i kj/mm (2 (43 kj/in. kj/in.) Ntch acuity (mrr Temperature at lading ( C) Heat input (k /mm) ) ''Ranking, = highest critical stress, 6 = lwest critical stress; cnditins 4, 7 and 8 nt ranked as nly ne steel was tested. WELDING RESEARCH SUPPLEMENT I 7s

8 Figs. 3, 7 and. An bservatin based upn the investigatin f the effect f the varius methds f perfrming the implant test shuld be nted. The steels used fr the evaluatin all have minimum yield strength f apprximately 48 MPa (7 ksi) and ultimate tensile strengths f apprximately 62 MPa (9 ksi). Table 8 shws that sme f the measured critical stress values apprach the yield and/r ultimate tensile strength f the steels. This is particularly true fr test cnditin 6, which is the cmbinatin f parameters mst frequently cited in the literature. By cmparisn, the critical stress values fr the same steels fund using test cnditin 3 (the Climax prcedure) are always well belw the yield r ultimate strength f the steel. This becmes imprtant when implant testing steels having a very lw susceptibility t hydrgenassisted cracking, such as steels A and B. The criterin used in the implant test as presented here is that specimen fracture must ccur at the intersectin f the helical ntch and the HAZ. Hwever, because the abslute value f the ntched tensile stress is higher than that f the unntched tensile stress, specimen failure can ccur alng the length f the implant specimen instead f in the desired lcatin if test parameters are relatively mild, resulting in an invalid test and a wasted test specimen. This phenmenn was bserved numerus times in the curse f this investigatin. Thus, since the relative ranking f steels in the implant test seems t be independent f the testing parameters, it is recmmended that as severe a test as pssible be perfrmed. Cnclusins. Hydrgen assisted cracking susceptibility can be evaluated by using the implant test. Hwever, n statistically significant crrelatin culd be fund that wuld relate hydrgenassisted cracking susceptibility t steel cmpsitin using the implant test. 2. Perfrming the implant test using a variety f parameters did nt significantly alter the relative ranking f the steels. 3. Fur previusly published carbn equivalent equatins culd nt predict the ranking f steels as determined by either implant r micrhardness tests. 4. Due t the fact that mild test parameters can require applied stresses apprximately the same as the yield and/r ultimate tensile strength f a steel t prduce specimen failure, it is recmmended that the implant test be perfrmed using severe test parameters.. Based upn the results f this investigatin, it seems unlikely that the hydrgenassisted cracking susceptibility f a mdern micrallyed pipeline steel can be determined slely frm cmpsitin. Fr this reasn, it is recmmended that carbn equivalent equatins nt play a majr rle when selecting a pipeline steel. Acknwledgements The authr expresses his appreciatin t R. G. Scheitz fr his assistance in perfrming the experimental wrk. References. Granjn, H The implants methd fr studying the weldability f high strength steels Meta! Cnstructin and British Welding lurnal II: SubCmmissin IXB. Recmmendatins fr the use f implant test as a cmplementary infrmatin test n the cld cracking susceptibility during the welding f steels. IIW Dcument IX It Y. and Bessy, K Weldability frmula f highstrength steels related t heataffected zne cracking. IIW Dcument IX7668: The Sumitm Search, N., May. 4. Duren, C. F. Significance f the implant test fr assessment f the field weldability f largediameter pipes. Mannesmann Research Institute, Duisburg, FRG.. Tanaka, J. and Kitada, T. Implant test fr studying cld cracking. IIW Dcument IX Inagaki, M.; Satch K.; Matsui, S.; and hkuma, Y. Applicatin f implant test n cld cracking. IIW Dcument IX It, Y.; Ikeda, M.; and Nakanishi, M Study n estimatin f lwer critical stress fr cld cracking at welds by implant test methd. The Sumitm Search, N. 7, May: Matsui, S. and Inagaki, M. Recent trend f research n cld cracking with implant test in Japan. IIW Dcument IX Meyer, L., and deber, H Review f HSLA plate metallurgyallying, nrmalizing, cntrlled rlling. Welding f HSLA (Micrallyed) Structural Steels: Metals Park, hi. American Sciety fr Metals. Crrectin Refer t Technical Nte: Effect f Weld Pl Cnfiguratin n HeatAffected Zne Shape by S. S. Clickstein and E. Friedman, June 98 Welding Research Supplement, pages s t 2s. The equatin at the tp f the st clumn n page 2s shuld have been shwn as fllws where the delta symbls (8) are t be interpreted as partial derivative signs: 8/. T\ S /, ST\ ST Als, T(r,z,t) shwn in righthand clumn, page s shuld be written tgether n ne line. 76sl SEPTEMBER 98