10. Testing of Welded Joints

Transcription

1 1. Testing of Welded Joints

2 S S S S S S S S S S 1. Testing of Welded Joints 126 d = specimen dimeter d 1 = hed dimeter depending on clmping device L C = test length = L + d/2 r = 2 mm r r L s L L c L t L O L C L t in test re in test re totl length L t depends on test unit hed width width of prllel length pltes 12 with 2 25 with > 2 tues 6 with D 5 12 with 5 < D 168,3 prllel length 1 ) 2 ) L c L S + 6 rdius of throt r 25 1 ) for pressure welding nd em welding, L S =. 2 ) for some other metllic mterils (e.g.luminium, copper nd their lloys) L c L S +1 my e required r-er1-1.cdr Figure 1.1 R m R eh R el f d L = mesurement length (L = k S with k = 5,65) L t = totl length S = initil cross-section within test length d 1 Flt nd Round Tensile Test Specimen to EN 895, EN 876, nd EN The sic test for determintion of mteril ehviour is the tensile test. Generlly, it is crried out using round specimen. When determining the strength of welded joint, lso stndrdised flt specimens re used. Figure 1.1 shows oth stndrd specimen shpes for tht test. A specimen is ruptured y test mchine while the ctul force nd the elongtion of the specimen is mesured. With these mesurement vlues, tension σ nd strin ε re clculted. If σ is plotted over ε, the drwn digrm is typicl for this test, Figure 1.2. Normlly, if steel with cc lttice structure is tested, curve with cler yield point is otined (upper picture). Steels with fcc lttice structure show curve without yield point. The most importnt chrcteristic vlues which re determined y this test re: yield stress R el, tensile strength R m, nd elongtion A. R m R P,2 R P,1 f A Lud r-er1-2.cdr A g,2 %,1 % A g A A Stress-Strin Digrm With nd Without Distinct Yield Point To determine the deformility of weld, ending test to DIN EN 91 is used, Figure 1.3. In this test, the specimen is put onto two supporting rollers nd former is pressed through etween the rollers. The distnce of the supporting rollers is L f = d + 3 (former dimeter + three times specimen thickness). The ckside of the specimen (tension side) is oserved. If surfce crck develops, the test will e stopped nd the ngle to which the specimen could e ent is mesured. The Figure 1.2

3 1. Testing of Welded Joints 127 test result is the ending ngle nd the dimeter of the used former. A ending ngle of 18 is reched, if the specimen is pressed through the supporting rollers without development of crck. In Figure 1.3 specimen shpes of this test re shown. Depending on the direction the weld is ent, one distinguishes (from top to ottom) trnsverse, side, nd longitudinl ending specimen. The tension side of ll three specimen types is mchined to eliminte ny influences on the test through notch effects. Specimen thickness of trnsverse nd longitudinl specimens is the plte thickness. Side ending specimens re normlly only used with very thick pltes, here the specimen thickness is fixed t 1 mm. A determintion of the toughness of mteril or welded joint is crried out Figure 1.3 with the notched r impct test. A cuoid specimen with V-notch is plced on support nd then hit y pendulum rm of the impct testing mchine (with very tough mterils, the specimen will e ent nd drwn through the supports). The used energy is mesured. Figure 1.4 represents smple shpe, notch shpe (Iso-Vspecimen), nd schemtic presenttion of test results. Figure 1.4

4 1. Testing of Welded Joints 128 Designtion Weld centre Designtion Fusion line/onding zone VWS / VWT / VWT / VWT / VWT / Dicke Dicke RL VWS / (fusion weld) VHT / VHT / V = Chrpy-V notch W = notch in weld metl; reference line is centre line of weld H = notch in het ffected zone; reference line is fusion line or onding zone (notch should e in het ffected zone) S = notched re prllel to surfce T = notch through thickness = distnce of notch centre from reference line (if is on centre line of weld, = nd should e mrked) = distnce etween top side of welded joint nd nerest surfce of the specimen (if is on the weld surfce, then = nd should e mrked) r-er1-5.cdr RL RL VHT / VHT / Position of Chrpy-V Impct Test Specimen in Welded Joints to EN 875 RL RL RL Three specimens re tested t ech test temperture, nd the verge vlues s well s the rnge of sctter re entered on the impct energy-temperture digrm (A V -T curve). This grph is divided into n re of high impct energy vlues, trnsition rnge, nd n re of low vlues. A trnsition temperture is ssigned to the trnsition rnge, i.e. the rpid drop of toughness vlues. When the temperture flls elow this trnsition temperture, trnsition of tough to rittle frcture ehviour tkes plce. As this steep drop mostly extends cross certin re, precise ssignment of trnsition temperture cnnot e crried out. Following DIN 5 115, three definitions of the Figure 1.5 trnsition temperture re useful, i.e. to fix T Ü to: 1.) temperture where the level of impct vlues is hlf of the level of the high rnge, 2.) temperture, where the frcture re of the specimen shows still 5% of tough frcture ehviour 3.) temperture with n impct energy vlue of 27 J. Figure 1.5 illustrtes specimen position nd notch position relted to the weld ccording to DIN EN 875. By modifying the notch position, the impct energy of the individul res like HAZ, fusion line, weld metl, nd se metl cn e determined in reltively ccurte wy. Figure 1.6 presents the influence of vrious lloy elements on the A V -T - curve. Three siclly different influences cn e seen. Incresing mngnese contents increse the impct vlues in the re of the high level nd move the trnsition temperture to lower vlues. The vlues of the low levels remin unchnged, thus the steepness of the drop ecomes clerer with incresing Mn-content. Cron cts exctly in the opposite wy. An incresing cron content increses the trnsition temperture nd lowers the vlues of the high level, the steel ecomes more rittle. Nickel decreses slightly the vlues of the high level, ut increses the

5 1. Testing of Welded Joints 129 Chrpy impct energy A V J J 1 13% Ni 8,5% 27 5% 3,5% 2 J 1 27 r-er1-6.cdr Figure 1.6 vlues of the low level with incresing content. Strting with certin Nickel content (depends lso from other lloy elements), steep drop does not hppen, even t lowest temperture the steel shows tough frcture ehviour. In Figure 1.7, the A V -T curves of some commonly used steels re collected. These curves re mrked with points for impct energy vlues of A V = 27 J s well s with points where the level of impct energy hs fllen to hlf of the high level. It cn clerly e seen tht mild steels hve the lowest impct energy vlues together with the highest trnsition temperture. The development of finegrin structurl steels resulted in cler improvement of impct energy vlues nd in ddition, the ppliction of such steels could e extended to considerly lower temperture rnge. specimen position: core longitudinl 2% Ni specimen shpe: ISO V % Ni C 1 Temperture Influence of Mn, Ni, nd C on the A -T-Curve v With the exmple of the steels St E 355 nd St E 69 it is clerly visile tht n increse of strength goes mostly hnd in hnd with decrese of the impct energy level. Another improvement showed the ppliction of thermomechnicl tretment (controlled rolling during het tretment). The ppliction of this tretment resulted in n increse of strength nd 2% Mn 1% Mn,5% Mn % Mn,1% C,4% C,8% C Figure 1.7

6 1. Testing of Welded Joints 13 impct energy vlues together with prllel sving of lloy elements. To mke comprison, the A V -T - curve of the cryogenic nd high lloyed steel X8Ni9 ws plotted onto the digrm. The mteril is tested under very high test speed in the impct energy test, thus there re no relile findings out crck growth nd frcture mechnisms. Figure 1.8 shows two commonly used specimen shpes for frcture mechnics test to determine crck initition nd crck growth. The lower figure to the right shows possiility how to oserve crck propgtion in compct tensile specimen. During the test, current I flows through the specimen, nd the tension drop ove the notch is mesured. C C L h 1,25h ±,13 P P,55h ±,25 1,2h ±,25 CT - specimen specimen width specimen height h = 2 ±,25 totl crck length = (,5 ±,5)h test lod P 2,1h 2,1h S specimen width smple height h = 2 ±,5 F,U crck initition U O h ering distnce S = 4h U SENB 3PB -specimen totl crck length = (,5 ±,5)h F U E,E U V r-er1-8.cdr V As soon s crck propgtes through the mteril, the current conveying cross section decreses, resulting in n incresed voltge drop. Below to the left mesurement grph of such test is shown. If the force F is plotted cross the widening V, the drwn curve does not indicte precisely the crck initition. r-er-1-9.cdr Figure 1.9 d F h Hrdness Testing to Brinell nd Vickers d1 F d 2 Figure 1.8 Frcture Mechnics Test Smple Shpe nd Evlution Anlogous to the stressstrin digrm, decrese of force is cused y reduction of the stressed cross-section. If the voltge drop is plotted over the force, then the strt of crck initition cn e determined with suitle ccurcy, nd the crck propgtion cn e oserved.

7 1. Testing of Welded Joints 131 Another typicl chrcteristic of mteril ehviour is the hrdness of the workpiece. Figure 1.9 shows hrdness test methods to Brinell (stndrdised to DIN 5 351) nd Vickers (DIN 5 133). When testing to Brinell, steel ll is pressed with known lod to the surfce of the tested workpiece. The dimeter of the resulting impression is mesured nd is mgnitude of hrdness. The hrdness vlue is clculted from test lod, ll dimeter, nd dimeter of rim of the impression (you find the formuls in the stndrds). The hrdness informtion contins in ddition to the hrdness mgnitude the ll dimeter in mm, pplied lod in kp nd time of influence of the test lod in s. This informtion is not required for ll dimeter of 1 mm, test lod of 3 kp (2942 N), nd time of influence of 1 to 15 s. This hrdness test method my e used only on soft mterils up to 45 BHN (Brinell Hrdness Numer).,2 mm ,2 mm Hrdness testing to Vickers is nlogous. This method is stndrdised to DIN Insted of ll, dimond pyrmid is pressed into the workpiece. The lengths of the two digonls of the impression re mesured nd the hrdness vlue is clculted from their verge nd the test lod. The impressions of the test ody re lwys geometriclly similr, so tht the hrdness vlue is normlly independent from the size of the test lod. In prctice, there is hrdness increse under lower test lod ecuse of n increse of the elstic prt of the deformtion.,2 mm 1 hrdness scle 6 Arevition 7 specimen surfce 8,9 1 reference level for mesurement,2 mm 13 3 hrdness scle Hrdness Test to Rockwell 6 7 specimen surfce 1 - cone ngle = 12 ll dimeter = 1,5875 mm ( 1 / 16 inch) 2-3 F 4 F 1 5 F 6 t 7 t 1 8 t 9 e 1 r-er1-1.cdr HRC HRA Figure 1.1 rdius of curvture of cone tip =,2 mm test prelod test lod totl test lod = F + F 1 Rockwell hrdness = 1 - e Terms HRB HRF 8,9 1 reference level for mesurement penetrtion depth in mm under test prelod F. This defines the reference level for mesurement of t. totl penetrtionn depth in mm under test lod F 1 resulting penetrtion depth in mm, mesured fter relese of F 1 to F resulting penetrtion depth, expressed in units of,2 mm: e = t /,2 Rockwell hrdness = 13 - e Hrdness testing to Vickers is lmost universlly pplicle. It covers the entire rnge of mterils (from 3 VHN for led up to 15 VHN for hrd metl). In ddition, hrdness test cn e crried out in the micro-rnge or with thin lyers. Figure 1.1 illustrtes hrdness test to Rockwell. In DIN 513 re vrious methods stndrdised which re sed on the sme principle.

8 1. Testing of Welded Joints 132 With this method, the penetrtion depth of penetrtor is mesured. At first, the penetrtor is put on the workpiece y ppliction of pre-test lod. The purpose is to get firm contct etween workpiece nd penetrtor nd to compenste for possile ply of the device. Then the test lod is pplied in shock-free wy (t lest four times the pre-force) nd held for certin time. Afterwrds it is relesed to rech minor lod. The remining penetrtion depth is chrcteristic for the hrdness. If the disply instrument is suitly scled, the hrdness vlue cn e red-out directly. All hrdness test methods to Rockwell use ll (dimeter mm, equiv. to 1/16 Inch) or dimond sphero-conicl penetrtor (cone ngle 12 ) s the penetrting ody. There re differences in size of pre- nd test lod, so different test methods re scled for different hrdness rnges. The most commonly used scle methods re Rockwell B nd C. The most considerle dvntge of these test methods compred with Vickers nd Brinell re the low time durtion nd possile fully-utomtic mesurement vlue recognition. The disdvntge is the reduced ccurcy in contrst to the other methods. Mesured hrdness numers re only comprle under identicl conditions nd with the sme test method. A comprison of hrdness vlues which were determined with different methods cn only e crried out for similr mterils. A conversion of hrdness vlues of different methods cn e crried out for steel nd cst steel ccording to tle in DIN 515. A reltion of hrdness nd tensile strength is lso given in tht tle. piston All the hrdness test methods descried ove require coupon which must e tken from the workpiece nd whose hrdness is then determined in test mchine. If workpiece on-site is to e tested, dynmicl hrdness test method will e pplied. The dvntge of these methods is tht mesurements cn e tken on completed constructions with hndheld r-er1-11.cdr reference r specimen Poldi - Hmmer Figure 1.11

9 1. Testing of Welded Joints 133 units in ny position. Figure 1.11 illustrtes hrdness test using Poldi-Hmmer. With this (out of dte) method, the mesurement is crried out y comprison of the workpiece hrdness with clirtion piece. For this purpose clirtion r of exctly determined hrdness is inserted into the unit, which is held y spring force ply-free etween piston nd penetrtor (steel ll, 1 mm dimeter). The unit is put on the workpiece to e tested. By hmmerlow to the piston, the penetrtor penetrtes the workpiece nd the clirtion pin simultneously. The size of oth impressions is mesured nd with the known hrdness of the clirtion r the hrdness of the workpiece cn e determined. However, there re mny sources of errors with this method which my influence the test result, e.g. n inclined resting of the unit on the surfce or hmmerlow which is not in line with the device xis. The mjor source of errors is the mesurement of the ll impression on the workpiece. On one hnd, the edge of the impression is often unshrp ecuse of the gret ll dimeter, on the other hnd the mesurement of the impression using mgnifying glsses is sujected to serious errors. Figure 1.12 shows modern mesurement method which works with ultrsound nd comines high flexiility with esy hndling nd high ccurcy. Here test tip is pressed mnully ginst workpiece. If defined test lod is pssed, spring mechnism inside the test Test force 5. kp r-er1-12.cdr 5 kp Federweg - little work on surfce preprtion of specimens (test force 5 kp) - Dt Logger for storge of severl thousnds of mesurement points - interfces for connection of computers or printers - for hrdness testing on site in confined loctions tip is triggered nd the mesurement strts. The mesurement principle is sed on mesurement of dmping chrcteristics in the steel. The mesurement tip is excited to emit ultrsonic oscilltions y piezoelectric crystl. The test tip (dimond pyrmid) penetrtes the workpiece under the test pressure cused y the spring force. With incresing penetrtion depth the dmping of the ultrsonic oscilltion chnges nd consequently the frequency. This chnge is mesured y the device. The dmping of the ultrsonic oscilltion depends directly on penetrtion depth thus eing mesure for mteril hrdness. The disply cn e clirted for ll commonly used mesurement methods, mes- Figure 1.12

10 1. Testing of Welded Joints 134 urement is crried out quickly nd esily. Mesurements cn lso e crried out in confined spces. This mesurement method is not yet stndrdised. σ > σ m σ m = σ pulstion rnge (compression) σ < σ m compression - + tension σ m = lternting rnge σ < σ m Wöhler line σ = σ m σ > σ m pulstion rnge (tension) time Description Dye penetrnt method crck is free, surfce is clen crck nd surfce with penetrnt liquid clened surfce, dye penetrnt liquid in crck surfce with developer shows the crck y coloring Appliction ll mterils with surfce crcks Mgnetic prticle testing Stress σ σ D II filure line III I A workpiece is plced etween the poles of mgnet or solenoid. Defective prts distur the power flux. Iron prticles re collected Ftigue strength (endurnce) numer lg N I re of overlod with mteril dmge II re of overlod without mteril dmge III re of lod elow ftigue strength limit Surfce crcks nd crcks up to 4 mm elow surfce. However: Only mgnetizle mterils nd only for crcks perpendiculr to power lines r-er1-13.cdr r-er1-14.cdr Ftigue Strength Testing Figure 1.13 Figure 1.14 To test workpiece under oscillting stress, the ftigue test is stndrdised in DIN 51. Mostly ftigue strength is determined y the Wöhler procedure. Here some specimens (normlly 6 to 1) re exposed to n oscillting stress nd the numer of endured oscilltions until rupture is determined (endurnce numer, numer of cycles to filure). Depending on where the specimen is to e stressed in the rnge of pulsting tensile stresses, lternting stresses, or pulsting compressive stresses, the men stress (or su stress) of specimen group is kept constnt nd the stress mplitude (or upper stress) is vried from specimen to specimen, Figure In this wy, the stress mplitude cn e determined with given medium stress (prestress) which cn persist for infinite time without dmge (in the test: 1 7 times). Test results re presented in ftigue strength digrms (see lso DIN 5 1). As n exmple the extended Wöhler digrm is shown in Figure The upper line, the Wöhler line, indictes fter how mny cycles the specimen ruptures under tension mplitude σ. The

11 1. Testing of Welded Joints 135 Description X-ry or isotope rdition penetrte workpiece. The thicker the workpiece, the weker the rdition reching the underside. Appliction Minly for defects with orienttion in rdition direction. Wire dimeter Tolerted devition Wire numer mm mm 3,2 1 2,5 ±, ,6 4 1, ±,2 6,8 7,63 8,5 9,4 1,32 11 ±,1,25 12,2 13,16 14, ±,5,1 16 Arevition Wire numer to Tle 1 Wire length mm Wire mteril Mteril groups to e tested rdition source workpiece film (displyed in distnce from workpiece) defect in rdition direction; difficult to identify (flnk lck of fusion) defect in rdition direction; esy to identify FE 1/7 1 to 7 5 FE 6/12 6 to 12 5 or 25 FE 1/16 1 to 16 5 or 25 CU 1/7 1 to 7 5 CU 6/12 6 to 12 5 CU 1/16 1 to 16 5 or 25 AL 1/7 1 to 7 5 AL 6/12 6 to 12 5 AL 1/16 1 to 16 5 or 25 mild steel copper luminium iron mterils copper, zink, tin nd its lloys luminium nd its lloys r-er1-15.cdr r-er1-16.cdr Non-Destructive Test Methods Rdiogrphic Testing Determintion of Picture Qulity Numer to DIN 5415 Figure 1.15 Description US-hed genertes high-frequency sound wves, which re trnsferred vi oil coupling to the workpiece. Sound wves re reflected on interfces (echo). Appliction Minly for defects with n orienttion trnsverse to sound input direction. Figure 1.16 dmge line indictes nlogously, when dmge to the mteril strts in form of crcks. Below this line, mteril dmge does not occur. À Á Â Ä r-er1-17.cdr Å Æ ³ À sound hed Á oil coupling  workpiece à defect Ä ultrsonic test device Å rdition pulse Æ defect echo ³ ckwll echo Non-Destructive Test Methods Ultrsonic Testing II à Test methods descried ove require specimens tken out of the workpiece nd prtly very ccurte smple preprtion. A testing of completed welded constructions is impossile, ecuse this would require destruction of the workpiece. This is the reson why vrious non-destructive test methods were developed, which re not used to determine technologicl properties ut test the workpiece for defects. Figure 1.14 shows Figure 1.17

12 1. Testing of Welded Joints 136 two methods to test workpiece for surfce defects. Figure 1.15 illustrtes the principle of rdiogrphic testing which llows to identify lso defects in the middle of weld. The size of the minimum detectle defects depends gretly on the intensity of rdition, which must e dpted to the thickness of the workpiece to e rdited. As the film with documented defects does not permit n estimtion of the plte thickness, scle r must e shown for estimtion of the defect size. Figure 1.18 Figure 1.18 For tht purpose, plstic templte is put on the workpiece efore rdition which contins metl wires with different thickness nd incorported metllic mrks, Figure The size of the thinnest recognisle wire indictes the size of the smllest visile defect. Rdition testing provides informtion out the defect position in the plte plne, ut not out the position within the thickness depth. A cler dvntge is the good documenttion ility of defects. An informtion out the depth of the defect is provided y testing the workpiece with ultrsound. The principle is shown in Figures 1.17 nd 1.18 (principle of sonr). The disply of originl pulse, ckwll nd defect echo is crried out with n oscilloscope. r-er1-19.cdr Figure 1.19 Ultrsonic Testing of Fillet Welds

13 1. Testing of Welded Joints 137 This method provides not only perpendiculr sound test, ut lso inccessile regions cn e tested with the use of so clled ngle testing heds, Figure Pores etween 1 nd 2 mm depth provide n unroken echo sequence cross the entire disply strting from 1mm. The ckwll echo sequence of 3 mm is not yet visile. Echo sequence of 2 mm depth. The ckwll is completely screened. Wll thickness is elow 4 mm. The roughness provides smller nd wider echos. 4 The olique nd rough defect from 2 to 3 mm provides wide echo of 2 to 3 mm. Strting with SKW 4, n unroken echo sequence follows. The inclintion of the reflector is recornised y chnge of the 1st echo when shifting the test hed. Echo sequence of 1 mm depth. The reflector in 3 mm depth is completely screened. The perpendiculr crck penetrting the mteril does not provide disply ecuse the reflecting surfce (tip of crck) is too smll. The olique ckwll reflects the soundwves ginst the crck. this is the reson why n impossile depth of 65 mm is displyed. r-er1-2.cdr r-er1-21.cdr Defect Identifiction with Ultrsound Defect Identifiction With Ultrsound Figure.1.2 Figure 1.21 Figures 1.2 nd 1.21 show schemticlly the mcro section disply of vrious defects se mteril ferrite + perlite corse grin zone 5 µ inite on n oscilloscope. A correct interprettion of ll the signls requires gret ex- 2,5 mm perience, ecuse the fine grin zone ferrite + perlite weld metl cst structure fusion line Steel: S355N (T StE 355) inite shpe of the displyed signls is often not so cler. r-er1-22.cdr Figure 1.22 Metllogrphic Exmintion of Weld Figure 1.22 illustrtes the potentil of metllogrphic exmintion. Grinding nd

14 1. Testing of Welded Joints 138 etching with n cid mkes the microstructure visile. The reson is tht depending on structure nd orienttion, the individul grins rect very differently to the cid ttck thus 1 % Ni % Cr Ni Cr Fe 1 % Fe reflecting the light in different wy. The mcrosection, i.e. without mgnifiction, gives complete survey out the weld nd fusion line, size of the HAZ, nd sequence of solidifiction. Under dequte mgnifiction, these res cn still not e distinguished precisely, however, n ssessment of the developed 4 5 microstructure is possile. 2 r-er1-23.cdr Figure m 1 1 Distnce from fusion line Micro-Anlysis of the Trnsition Zone Bse Mteril - Strip Cldding An ssessment of the distriution of lloy elements cross the welded joint cn e crried out y the electron em micro-nlysis. An exmple of such n nlysis is shown in Figure If solid ody is exposed to focused electron em of high energy, its toms re excited to rdite X-rys. There is simple reltion etween the wve length of this rdition nd the tomic numer of the chemicl elements. As the intensity of the rdition depends on the concentrtion of the elements, the chemicl composition of the solid ody cn e concluded from survey of the emitted X-ry spectrum qulittively nd quntittively. A detection limit is out.1 mss % with this method. Microstructure res of minimum dimeter of out 5 µm cn e nlysed. If the electron em is moved cross the specimen (or the specimen under the em), the element distriution long line cross the weld r-er-1-24.cdr Figure weld 1. weld xis of ending former Struß - Test 1 weld Agents: - electrolytic copper in the form of chips (min. 5 g/l test solution) - 1 ml H2SO 4 diluted with 1 l wter nd then. 11 g CuSO 5 H O re dded 2 Test: The specimens remin for 15 h in the oiling test solution. Then the specimens re ent cross former up to n ngle of 9 nd finlly exmined for grin filure under 6 to 1 times mgnifiction xis of ending former

15 1. Testing of Welded Joints 139 solid ody cn e determined. Figure 1.23 presents the distriution of Ni, Cr, nd Fe in the trnsition zone of n ustenitic plting in ferritic se metl. The upper prt shows the relted microsection which elongs to the nlysed prt. This micronlysis ws crried out long stright line etween two impressions of Vickers hrdness test. The impressions re lso used s mrk to identify precisely the re to e nlysed. The so clled Struß test is 12 stndrdised in DIN 5 we 914. it serves to determine 8 se plte tck welds mesurement points the resistnce of weld ginst intergrnulr corro- weld2 weld sion. Figure 1.24 shows 12 the specimen shpe which 8 12 is normlly used for tht test. In ddition, some de- r-er-1-25.cdr Test of Crck Susceptiility of Welding Filler Mterils to DIN 5129 tils of the test method re explined. Figure 1.25 Figure 1.25 presents specimen shpe for testing the crck susceptiility of welding consumles. For this test, weld numer 1 is welded first. The 2. weld is welded not lter thn 2 s in reversed direction fter completion of the first weld. Throt thickness of weld 2 must e 2% elow of weld 1. After cooling down, the eds tensioning olt hexgon nut min. M12 DIN 934 tensioning plte guidnce pltes re exmined for crcks. If crcks re found in weld 1, the test is void. If weld 1 is specimen free from crcks, weld 2 is se ody exmined for crck with mgnifying glsses. Then weld 1 is mchined off nd weld 2 is crcked y end- r-er-1-26.cdr Tensioning Specimen for Crck Susceptiility Test ing the weld from the root. Test results record ny Figure 1.26

16 1. Testing of Welded Joints 14 surfce nd root crcks together with informtion out position, orienttion, numer, nd length. The welding consumle is regrded s 'non-crck-susceptile' if the welds of this test re free from crcks. Figure 1.26 presents two proposls for self-stressing specimens for plte tests regrding their hot crck tendency. Such tests re not yet stndrdised to DIN. thermo couple groove shpe cross-section electrode Wd./2 Wd. Wd./2 6 H 6 weld metl Hc support plte implnt welding direction 2 2 lod specimen shpe temperture in C T mx lod in N strt end crter crck coefficient 15 c C = x 1 (in %) sections nchor weld test weld nchor weld t 8/5 time in s rupture time r-er1-27.cdr r-er1-28.cdr Tekken Test Implnt Test Figure 1.27 Figure 1.28 There re vrious tests to exmine cold crck tendency of welded joints. The most importnt ones re the self-stressing Tekken test nd the Implnt test where the stress comes from n externl source. In the Tekken test which is stndrdised in Jpn, two pltes re coupled with nchor joints t the ends s step in joint preprtion see Figure Then test ed is welded long the centre line. After storing the specimen for 48 hours, it is exmined for surfce crcks. For more precise exmintion, vrious trnsverse sections re plnned. The vlue to e determined is the minimum working temperture t which crcks no longer occur. The specimen shpe simultes the conditions during welding of root pss.

17 1. Testing of Welded Joints 141 The most commonly used cold crck test is the Implnt test, Figure A cylindricl ody (Implnt) is inserted into the ore hole of support plte nd fixed y surfce ed. After the ed hs cooled down to 15 C the implnt is exposed to constnt lod. The time is mesured until rupture or crck occurs (depending on test criterion 'rupture' or 'crck'). Vrying the lod provides the possiility to determine the stress which cn e orn for 16 hours without ppernce of crck or rupture. If stress is specified to e of the size of the yield point s requirement, prehet temperture cn e determined y vrying the working temperture to the point t which crcks no longer pper. As explined in chpter 'cold crcks' the hydrogen content plys n importnt role for cold crck development. Figure 1.29 shows results of trils where the cold crck ehviour ws exmined using the Tekken nd Implnt test. Vriles of these tests were hydrogen content of the weld metl nd prehet temperture. The vrition of the hydrogen content of the weld metl ws crried out y different exposure to humidity (or reking) of the used stick electrodes. Bsed on the hydrogen content, the prehet temperture ws incresed test y test. Consequently, the curves of Figure 1.29 represent the limit curves for the relted test. Prehet temperture C r-er-1-29.cdr Figure 1.29 Implnt-Test R cr = R p,2 = 358 N/mm² frctured strting crcks crck-free ml/ g Specimens ove these curves remin free from crcks, elow these curves crcks re present. Evident for oth grphs is tht with incresed prehet temperture considerly higher hydrogen contents re tolerted without ny crck development ecuse of the much etter hydrogen effusion. If oth grphs re compred it ecomes ovious tht the tests produce slightly different findings, i.e. with identicl hydrogen content, the determined prehet tempertures required for the voidnce of crcking, differ y out 2 C. het input: 12 kj/cm sic coted stick electrode plte nd support plte thickness: 38 mm Prehet temperture C Diffusile hydrogen content Test Result Comprison of Implnt nd Tekken Test Tekken-Test strting crcks crck-free ml/ g

18 1. Testing of Welded Joints 142 Figure 1.3 illustrtes method to mesure the diffusile hydrogen content in welds which is stndrdised in DIN Figure ) shows the urette filled with mercury efore specimen is inserted. The coupons re inserted into the opened urette nd drwn with mgnet through the mercury to the cpillry side (density of steel is lower thn tht of mercury, coupons surfce). Then the urette is closed nd evcuted. The hydrogen, which effuses of the coupons ut does not diffuse through the mercury, collects in the cpillry. The smples remin in the evcuted urette 72 hours for degssing. To determine the hydrogen volume the urette is ventilted nd the coupons re removed from the cpillry side. The volume of the effused hydrogen cn e red out from the cpillry; the height difference of the two mercury menisci, the ir pressure, nd the temperture provide the dt to clculte the norm volume under stndrd conditions. This volume nd the coupons weight re used to clculte, s mesured vlue, the hydrogen volume in ml/1 g weld metl. This is the most commonly used method to determine the hydrogen content in welded joints. to pump cpillry side mercury r-er-1-3.cdr Figure 1.3 ) strting condition hydrogen under reduced pressure coupons evcuted ) during degssing Burettes for Determintion of Diffusile Hydrogen Content V T ir pressure B meniskus1 M meniskus2 c) ventilted fter degssing