A Field Weldabi l i ty Test for Pipeline Steels-Part II

The slot weld test is shown to be a feasible shop test to determine the susceptibility of pipeline steels to

hydrogen-induced cracking

BY R. VASUDEVAN, R. D. STOUT AND A. W. PENSE

Introduction

Recently,1 a shop-type weldabil i ty test was developed to be more conve­nient for assessing the field weldabil i ty of pipeline steels than tests requiring elaborate laboratory facilities. The test was used to show the rate at which hydrogen-induced cracking takes place over intervals of time fol lowing welding and the benefit of moderate preheating toward preventing it. Al­though a number of carbon equivalent formulae have been proposed to date,-"4 they can be applied only to those compositions of steels for which they were developed and give erron­eous indications5"7 when they are applied to the newly developed low carbon (0.03-0.08%) microalloyed steels designed for high strength, excellent toughness and good weld­ability. A need exists for a simple test method that gives a more reliable indi­cation of the required welding condi­tions for avoiding hydrogen cracking than does the carbon equivalent for­mula.8"1?

The present investigation included studies of:

1. The combined effects of preheat (up to 120°C, i.e., 248°F) and time lapse after welding on the extent of cracking on a wide range of steels including those described as acicular ferrite, polygonal ferrite and reduced pearlite steels.

2. Modif icat ion of the specimen designs to develop a convenient meth­od of obtaining variable constraint.

3. Correlation between the labora­tory slot weld test results and full-size shop girth welded pipes at several values of time lapse and preheat tem­peratures.

4. Standardization of the fabricating

method to prepare specimens for field use.

Materials

The compositions of steels studied in the present investigation are listed in Table 1 and their mechanical prop­erties in Table 2. The microstructures of these steels varied from polygonal ferrite plus islands of pearlite or bain­ite, more or less banded, to acicular ferritic structures. Representative mi­crostructures of selected steels are shown in Fig. 1.

Effects of Time Lapse After Welding and Preheat

Experimental Procedure

The specimen design is reproduced in Fig. 2. All welds were deposited with 4 mm (%2 in.) diameter HYP E7010 electrodes at a current of 150 amperes (A) and 30 cm/minute (min) travel speed. The test plates were heated to the desired temperature, welded, and then held for specific periods of t ime, viz., 1 min, 5 min, 10 min, 20 min or 24 hours (h) before tempering (heat tint) to arrest cracking and to oxidize any crack previously formed. Preheating ranged from 20°C (68°F or R.T.) to

Paper to be presented at the AWS 61st Annual Meeting in Los Angeles, California, during April 14-18, 1980.

R. VASUDEVAN is with the Linde Division, Union Carbide Corporation, Ashtabula, Ohio; R. D. STOUT is Dean of the Graduate School, and A. W. PENSE is Professor of Metallurgy and Materials Engineering and Chairman of the Department of Metallurgy and Materials Science, Lehigh University, Bethlehem, Pennsylvania.

120°C (248° F). Welds were also made on selected

steels wi th 4 mm (%s in.) diameter E7018 electrodes wi th the same heat input to show the effect of low hydrogen concentration in the weld on the susceptibility of the steels to cracking. The E7018 electrodes were baked at 370°C (698° F) for 1 h and stored at 100°C (212°F) for at least 8 h before welding. Metallographic sec­tions were taken from the center of the slot weld test specimens to deter­mine the locus of crack init iation and growth.

Results and Discussion

Table 3 lists the extent of cracking, locus of crack and hardness of the coarse grained HAZ for the heats of steel in Table 1 for a welding condit ion of 20°C (68°F) preheat and 24 h time lapse. The results of the combined effect of preheat and t ime lapse on the extent of cracking for a number of susceptible heats of steel are pre­sented in Table 4.

It is evident from Table 3 that crack­ing levels from 0 to 80% were exhibited by the group of steels. The low crack­ing level in C10113 and absence of cracking in heat NKK may be attri­buted to their very low carbon con­tents. None of the heats exhibited cracking when welded with E7018 (low hydrogen) electrodes. The behav­ior of one particular steel, viz., heat A68-2, deserves noting. Three speci­mens of this heat gave 60% cracking whereas three others gave no cracking. Subsequent metallographic examina­tion revealed the presence of lamina­tion in specimens which gave 0% cracking whereas specimens which experienced 60% cracking did not have

76-s l M A R C H 1980

Table 1—Composition of Pipeline Steel Materials

Pipe Dimensions

Heat

63843 C10113 B319 98173 88284 B259 A68-2 492S1871 1376

Diameter, mm

900 1200 900 900 900 900 900

1050 Plate

Wal l , mm

14.3 18.3 15.7 14.3 19.0 15.7 11.4 14.6 19.0

C

0.25 0.05 0.24 0.21 0.21 0.08 0.22 0.26 0.12

Mn

1.30 2.04 1.25 1.30 1.19 1.15 1.38 1.36 1.00

P

0.010 0.010 0.012 0.018 0.013 0.020 0.025 0.011 0.008

S

0.025 0.006 0.024 0.019 0.021 0.004 0.005 0.025 0.007

Si

0.01 0.29 0.18 0.02 0.01 0.23 0.09 0.04 0.02

IF5913 IF5914 IF6221 2F1665 NKK

835

B229 B268

490S2441

Plate Plate Plate Plate Plate

Plate

600 600

1050

Cr

0.58

Ni

15.9

5.0 6.0

0.180 0.100

1.21 1.41

0.012 0.010

0.009 0.002

0.22 0.26

14.6 0.19 1.30 0.007 0.021 0.02

Mo

0.25 0.58

19.0 19.0 20.3 20.3 25.4

0.12 0.069 0.084 0.066 0.040

1.37 1.56 1.44 1.46 1.24

0.007 0.007 0.008 0.005 0.013

0.004 0.003 0.006 0.003 0.003

0.21 0.23 0.22 0.21 0.32

0.07 0.06 0.25 0.53 0.30

0.04 0.03 0.05 0.05 0.20

0.30 0.28 0.27 0.35

-

0.099 1.39 0.004 0.005 0.33 0.024 0.16 0.15

0.045

Cb

0.03

Others

Al = 0.04

----0.002 0.06 0.01

--— -0.050

0.095

0.02 0.065

0.023 0.031 0.031 0.050

< 0.005 0.031 0.019

0.048 0.050 0.052 0.053 0.020

0.025

0.019 0.035

----

Al = 0.011

-Cu = 0.34, M, = 0.011 Ce = 0.03, La = 0.014 Al = 0.012 Al = 0.013 Al = 0.014 Al = 0.018 Cu = 0.34, AI = 0.027 Cu = 0.017 Sn = 0.002 Ce = 0.007 Ce = 0.014 AI = 0.056, Ce = 0.017

0.026

any lamina t ion—Fig . 3.

From Tab le 3 a n d Fig. 4 it is also seen that the locus o f crack tends to w a n d e r b e t w e e n t h e H A Z , f us ion l i ne and w e l d meta l par t ly because o f t he stress pa t te rn at t h e roo t o f t h e n o t c h and par t ly because the w e l d meta l i tself is no t very crack resistant. This p o i n t is c o n f i r m e d by the presence o f m i c r o -cracks in t h e w e l d meta l as s h o w n in Fig. 5. The responses of t he steels to the w e l d t h e r m a l cyc le d i f fe r p r i n c i ­pal ly because the coarse g ra ined HAZ 's of t h e h igher ca rbon steels f o r m largely mar tens i t i c s t ruc tures whereas the l owe r c a r b o n heats d e v e l o p W i d ­mans ta t ten fer r i te and ba in i t i c s t ruc­tures as s h o w n in Fig, 6.

Results o f t he c o m b i n e d e f fec t o f preheat and t i m e lapse o n the ex ten t o f c rack ing (Tab le 4) s h o w that m o d e r ­ate preheat t empe ra tu res , o f t he o rder o f 65 to 100°C (149 to 212°F) , are e f fec t i ve in de l ay i ng the onset o f c rack ing l o n g e n o u g h to make it prac­t i cab le to depos i t the ho t pass be fo re the root pass exper iences c rack ing , even in t he m o r e ha rdenab le steels such as heats 63843 and 492S1871. A t 120°C (248°F) p reheat , c r a c k i n g was v i r tua l l y e l i m i n a t e d .

The data fo r each heat may be pre­sented in a g raph in w h i c h the a l l o w ­able t i m e lapse is s h o w n fo r a spec i f ied percen tage o f c rack ing at va r ious pre­heats. Figure 7 i l lustrates such a rela­t i o n s h i p fo r a c rack ing level of 10%. A ver t ica l e rec ted at a p rac t ica l t i m e lapse b e t w e e n roo t and ho t passes intersects t he curves at the requ i red preheat fo r each heat o f steel . This

t ype of analysis fac i l i ta tes se t t ing a schedu le o f p reheat a n d t i m e in te rva l b e t w e e n root and hot pass w e l d s tha t w i l l assure c rack - f ree w e l d s in f i e ld g i r th we lds .

V a r i a b l e C o n s t r a i n t

It is des i rab le to have the means o f va ry ing t he s p e c i m e n rest ra in t so t ha t test results can be ad jus ted to m a t c h f i e ld exper ience . Apar t f r o m m o v i n g the slot t o o n e side of the spec imen , 1

t w o o the r m e t h o d s of v a / y i n g restra int as n o t e d b e l o w w e r e e x a m i n e d :

1 . Reduc ing t h e w i d t h o f t h e spec i ­m e n .

2. C u t t i n g s ide slots i n t o t he regular slot w e l d test to var ious d e p t h s w e r e

e x a m i n e d . Heat IF5913 was chosen fo r tes t ing . Table 5 shows the var ious p la te

designs tes ted t o g e t h e r w i t h t h e ex ten t of c rack ing in the b r e a k - o p e n test as w e l l as t he locus o f c rack in a m e t a l l o ­g raph ic sec t ion cut ou t f r o m the c e n ­ter o f t h e s lot s p e c i m e n . It is seen tha t r educ ing t h e s p e c i m e n w i d t h f r o m 150 m m (5.9 in.) t o 100 m m (3.9 in.) l owers the c rack ing level f r o m 50% to a very l o w va lue w i t h o u t any change in hea t -a f fec ted z o n e or w e l d meta l hardness. C u t t i n g side slots i n to the p la te reduced the ex ten t o f c rack i ng p r o p o r ­t i ona l l y to the d e p t h of t he side slots. Thus, sat is factory m e t h o d s of ad jus t ­ing t he spec imen des ign d o exist to ma tch t h e spec imen restra int w i t h tha t

Table 2—Mechanical Properties of Some of the Pipeline Steels Studied (in Transverse Direction)

Heat

63843 a 0113 B319 98173 88284 B259 492S187I 1376 IF5913 IF5914 IF6221 2F1665 NKK 835 B229 B268

Yield stress, MPa

470 574 503 460 457 448 547 419 490 417 386 404 513 486 416 577

Tensile strength, MPa

675 772 601 630 638 507 688 574 645 564 602 626 591 595 583 635

Elongation in 50 mm, %

33 39 31 36 37 42 25 35

----54 44 33

—

W E L D I N G R E S E A R C H S U P P L E M E N T I 77-s

"^ 1m •.- J s p a > > w • i- .

'•} ;<yyff

H • •

1 A ~-t

&GT/J t492S1871

Xj

*. c-

1 : ^

V

i;ic>

-f ieat

X^s*."*"" . «\£ *" F/g. 1-Representative base metal microstructures: A-heat C10113; B-heat 492S1871; C-6259; D-heat NKK. Nital etch, X500

Table 3—Hydrogen Assisted Cracking Test Results with Slot Specimen, Locus of Crack Growth and Hardness of HAZ of the Steels Studied (Preheat = 20°C; Elapsed Time = 24 h)

Heat no.

63843 a 0113 B319 98173 88284 B259 A68-2 492S1871 1376 IF5913 IF5914 IF6221 2F1665 NKK 835 B229 B268 490S2441

"> HAZ-heal 'bl FL—fusion

Percent cracking

HYP E7010

50 25 40 25 20 Nil 60 80

0-70 50 Nil

0-10 0-3 Nil

0-10 30-35 15-20

5

affected zone. me.

"' WM—weld metal.

e n c o u n t e r e d in f i e ld jo in ts .

E7018

Nil Nil --— --Nil ---------—

w e l d e d

Coarse grained HAZ hardness, 1 kg load DPH

350 340 344 -

320 -

312 360 -

363 288 328 312 273 245 316 295 —

g i r t h

Locus of crack in the order of crack growth

HAZ ' a l -mos t l y FL"" Mostly in HAZ W M U , - F L - H A Z - F L

-H A Z - F L - W M No cracking WM—and mostly in HAZ H A Z - F L - W M

• -

H A Z - W M No cracking H A Z - W M All in HAZ No cracking Mostly in W M or no cracking WM—mostly in HAZ—finally in FL W M - m o s t l y in HAZ

—

Steer ing C o m m i t t e e m e m b e r s , espe­

cial iy Mr . W h i t e , it was ar ranged to

Correlation of Slot Weldabil i ty Test with Full-Size Shop-Welded Pipe

If the slot weldabil i ty test is to be useful in predicting the girth field welding behavior of pipeline steels, it is necessary to have available a direct correlation of the behavior of a given steel in the laboratory tests with its behavior in actual field welding. Through the cooperation of the API

have such a direct correlation con­ducted.

Experimental Procedure

The heat of steel used for this inves­tigation was 492S1871. The conditions and procedures fol lowed in shop welding of the pipes were as follows. Full-size pipes, w i th joint preparation and design as shown in Fig. 8, were assembled and welded by three weld­ers. Two welders, starting at the top, welded in opposite directions to the 3

Weld Over 2.4mm Slot

turn M t ' t U 1

h25 -+ 90mm '. 25H

Fig. 2—Slot weld test specimen design

Fig. 3-Cross sections of heat A 68-2 show­ing the absence of hydrogen cracking in a laminated region of the pipe steel. Nital etch, X5 (reduced 28% on reproduction)

and 9 o'clock positions on either side: the third welder started from the 3 o'clock position and welded the whole bottom half circumference. Next, after a 5 min lapse t ime after the root pass, the hot pass was laid on one of the top quarter sections. The other top quarter section was welded after a time lapse of 20 min after the root pass.

The pipe was then allowed to cool to ambient temperature and was then cut into half for shipment. Another pipe was welded wi th the same sequence except that the pipe was preheated before welding to a temper­ature of 66°C (151 °F). This procedure yielded six conditions, as fol lows, for further examination:

1. No preheat—5 min between root and hot pass.

2. No preheat—20 min between root and hot pass.

3. No preheat—no hot pass after root pass.

4. 66°C (151°F) preheat-5 min be-

78-sl M A R C H 1980

Table 4—Combined Effect of Preheat and Time

°c 20

65

80

95

120

Time lapse

24 h 20 min 10 min 5 min 1 min

24 h 20 min 10 min 5 min 1 min

24 h 20 min 10 min 5 min 1 min

24 h 20 min 10 min 5 min

24 h

492S1871

80% 50 50 40 10

45 4-6 4-6 3-5 1-2

45 1 2 1

-3-40

3 2 1

I

Lapse after

63843 '

50% 50 40 40 10

40 1-30 15 6 2

35 1-25

3 2

Nil

30 10 --1

Welding on the Extent of Hydrogen-Induced Cracking

B319

40% 35 30 15 s

13 1 1

--1

----1 ---Nil

Heat numbers

98173

25% 15

5-10 5-10

3

5 5 3 3 -5

Nil Nil

1 Nil

--

Nil

88284

20% 20 20 10

2

10 2 3 3

Nil

5 5 3

Nil

5 2

Nil

-Nil

C10113

25 5

-3

-20 Nil

Nil

IF5913

50 40-50

-5-10

-0-40 Nil

Nil

1376

0-70 1-2

-Nil

Nil

"For heat 63843: A l 80°C, 1 h lapse produced 30% cracking and 15 min produced 2%; at 65°C, 1 h lapse produced 35% cracking and 15 min produced 20%.

<,.,

• • • • : • < •

\;f* >

;ei [4

- - ' < • , . . . , . . -

Fig. 4-Locus of hydrogen crack initiation and growth in several steels: A-heat B229; B-heat B319; C—00113. Nital etch; X50 (reduced 28% on reproduction)

tween root and hot pass. 5. 66°C (151 °F) preheat-20 min

between root and hot pass. 6. 66°C (151 °F) preheat-no hot

pass after root pass. The shop-welded pipes were cut

into sections for metallographic exam­ination. For each test condit ion 12 sections were selected randomly to determine whether cracking oc­curred.

Results and Discussion

Data for the six conditions are pre­sented in Table 6. Figure 9 shows pho­tomicrographs of the extent and sever­ity of cracking observed in the girth welds deposited under four conditions in which cracking occurred. It is seen

from Fig. 9A that, for no preheat-no hot pass conditions, total failure of the root pass occurred. Such complete failures were not found for the other conditions. The frequency of cracking is maximum for the no preheat-no hot pass condit ion and is reduced either by shortening the time lapse between the root pass and hot pass or by pre­heating.

Figure 10 shows the correlation of test results between the shop girth-welded pipe and the laboratory slot weldability test. Since the extent of cracking in the f ield-welded pipe is of the same order-to-magnitude as that of the laboratory slot test, it appears that the slot weld test is able to assess the field weldabil i ty of pipeline steels usefully if somewhat conservatively.

Practical Methods of Shop Fabrication of the Specimen Test

Since the preliminary results of the slot weldabil ity test were published,' a number of laboratories have carried out weldability studies using the new­ly developed test to assess the feasibil­ity of the test as a reliable indicator of the susceptibility of pipeline steels to hydrogen-induced cracking. Although some laboratories11"13 have reported that the slot weldabil i ty test provides a simple and reproducible test to estab­lish welding parameters such as pre­heat and time interval between root and hot pass welds, others11"17 have reported lack of reproducibil ity in test, or excessive and sometimes total weld metal cracking. Some of the diff icul-

W E L D I N G RESEARCH SUPPLEMENT I 79-s

0

/

0)^m • •

><a Fig. 6—Representative microstructure ot the heat-affected zone coarse grained regions in root passes: A-heat 6229 (0.18% C); B-heat IF5913 (0.12% C); G-heat 835 (0.10% Q; D-heat NKK (0.04% C). Nital etch; X500 (reduced 28% on reproduction)

/ Heat 63843

/

w Fig. 5—Occurrence of microcracking in the root-pass weld metal deposited with E7010 electrode: A-heat IF5914; B-heat IF5913. Nital etch; X500 (reduced 28% on reproduc­tion)

ties that have been cited in the lack of field applicability of the test are as follows:

1. The slot in the specimen pro­duced by mil l ing for laboratory testing would be a difficult practice to con­duct in the fields

2. Although the specimens may be prepared by saw cutt ing from one end and welding that end wi th E7018 elec­trode leaving a 90 mm (3.54 in.) through-thickness open slot, a saw blade capable of producing a slot of the proper width (2.4 mm, i.e., 0.09 in.) was not available in the market.

Possible reasons for the lack of reproducibility and excessive weld metal cracking encountered in some of the studies cited above are as fol­lows:

1. During fabrication of the slot, it is possible that the slot width was

5 10 20 100 1000 Time (Mins)

Fig. 7—Effect of preheat on the time interval after welding for 10% cracking

reduced by contraction of the restraint weld beads so that the final slot width might have been less than the speci­fied 2.4 mm (0.09 in.). The sensitivity of the slot weld test to the width of the slot was observed during the early period of development of the slot wel­dability test18 wherein a slot width of 3.2 mm (Va in.) as well as zero gap (two 200 mm by 75 mm plates, i.e., 7.9 x 3 in., were abutted tightly together and welded over) produced extensive weld metal cracking as shown in Fig. 11. In either case the weld root exhibited a very sharp re-entrant angle (high stress

concentration). A slot width of 2.4 mm (0.09 in.) produced opt imum results.

2. Manual welding of the test weld with a longer-than-normal arc length produces an erratically shallow and wide bead which induces higher stresses on the weld and an unfavor­able weld configuration at the root of the notch. Note that all the tests con­ducted at Lehigh were performed using an automatic welding unit wherein the electrode has a tendency to dig in as it passes over the slot producing deep penetration and a nar­row bead.

80-s I M A R C H 1980

Table 5—Modifications of the Slot Weld Test and Its Effect on the Extent of Cracking"

Hardness, Hv Cracking in Crack extent and locus

1.

1. 3.

4.

break-open test, %

50

Traces 30

Approx. 10

in metallographic sec t ion" '

45-30% HAZ, 15% weld metal (see Sketch A)

Nil (see Sketch B) 40-15% HAZ, 25% weld metal

(see Sketch C) 15-10% HAZ, 5% weld metal

(see Sketch D)

In coarse grained HAZ

About 363

About 360

—

In weld metal

About 260

About 260

—

'^'Specimen tested: heat IF 5913; lapse time—24 h. ""Sketches corresponding to designations given in parentheses are as follows:

t* 9 0 mirH

y 75 mfrSH

<2>

D 1

1 1?

1 |

V

•

Fig. 9—Effect of welding conditions on cracking severity in shop-welded girth welds on heat 492S1871: A-no preheat, no hot pass; B—no preheat; hot pass 5 min later; C—no preheat, hot pass 20 min later; D-preheat 66°C (151°F). Picral etch

A supplementary program was un­dertaken to explore possible ways of alleviating the problems mentioned above.

Test Procedure

Fabricated test specimens made from 200 mm by 75 mm (77/sX 3 in.)

- I P *

Pipe 1 — No Preheat Pipe 2— 66°C Preheat

Fig. 8—Weld joint design and procedure for shop girth-welded pipes on heat 492S1871

strips saw cut from pipe (with the 200 mm (77s in.) dimension in the direc­tion of curvature of the pipe segment) were prepared from four heats in­cluded in the previous Lehigh tests run on machined slots. The heats were 492S1671, 88284, B319 and 490S2441, and the heats varied in cracking response from 2-3% for 490S2441 to 80% for 492S1871 after 24 h time lapse (Table 4). The results are reproduced in Table 7.

Specimens were fabricated accord­ing to the procedure shown in Fig. 12. They were first tack welded in place with wire spacers to hold the plates apart at the appropriate 2.4 mm (0.09 in.) gap. From this point three proce­dures were examined.

1. The wire spacers of 2.4 mm (0.09 in.) diameter were removed and the restraint welds were made on both sides (top and bottom) of the plate leaving an open slot length of 90 mm (3'/2 in.) at the center. The electrodes used for the restraint welds were E7018 which were previously baked at 370°C (698°F) f o r l h fol lowed by holding for at least 8 h at 100°C. A welding current of 190 A and a travel speed of 150 mm/min were used. This procedure resulted in substantial contraction dur­ing restraint welding, leaving a slot width of less than 1.6 mm (0.06 in.).

2. The wire spacers of 2.4 mm (0.09 in.) diameter were left in position dur­ing restraint welding. After restraint welds were completed, the center spacer was removed. This procedure resulted in a gap of 1.6 mm (0.06 in.) in the slot.

3. Wire spacers of 3.2 mm (Va in.) diameter, instead of 2.4 mm (0.09 in.), were used during tack welding. No center spacer was used. The spacers were not removed during restraint welding but were welded over on each

W E L D I N G RESEARCH SUPPLEMENT I 81-s

Table 6—Results of Metallographic Examination of Shop-Welded Pipes (Heat No. 492S1871)

Welding condi t ion

1. No preheat: no hot pass 2. No preheat; hot pass deposited 20 min after

the root pass 3. No preheat; hot pass deposited 5 min after

the root pass. 4. Preheat 66°C; no hot pass 5. Preheat 66°C; hot pass deposited 20 min

after root pass 6. Preheat 66°C; hot pass deposited 10 min

after root pass

Frequency of crack per 12 sections

examined

4

1

3 Ni l

(50%) (33%)

( 8%)

(25%)

s ide i n c o r p o r a t i n g t h e m in t h e re­straint w e l d . Th is left a gap o f 2.4 m m (0.09 in.) in t he slot. Restraint w e l d i n g was d o n e as in the above 1st p roce ­du re .

In o rder to see if t he s p e c i m e n d i m e n s i o n , i tself , has any e f fec t o n t h e extent of c rack ing w h e n the w i d t h o f t he slot was va r ied , a d d i t i o n a l tests w e r e p e r f o r m e d on heat 492S1871 by fab r i ca t i ng t h e test spec imens f r o m 200 m m (7% in.) by 62.5 m m (2.46 in.) str ips so as t o o b t a i n a f ina l p la te size o f 200 by 125 m m (7% x 5 in.) . Fabrica­t i o n was p e r f o r m e d a c c o r d i n g t o p r o ­cedu re 3 above using 2.4 m m (0.09 in.) and 3.2 m m (Va in.) spacers t o o b t a i n f ina l slot w i d t h s of 1.6 m m (0.06 in.) and 2.4 m m (0.09 in.) , respect ive ly . Tests w e r e also run o n heat 492S1871 us ing t h e 200 by 125 m m (-7% x 5 in.)

regular s lot w e l d test w i t h a m a c h i n e d slot of 2.4 m m (0.09 in.) w i d t h to p r o v i d e a basis for c o m p a r i s o n w i t h t he fab r i ca ted slot . Heat 492S1871 was o f pa r t i cu la r in terest , because th is was the o n l y heat o n w h i c h fu l l -s ize g i r th w e l d i n g was c o n d u c t e d a n d t h e ex ten t of c rack ing the reo f was p rev ious ly c o m p a r e d t o tha t o f t h e s tandard m a c h i n e d slot w e l d a b i l i t y test results.

A f te r p repa ra t i on o f t h e spec imens , test w e l d s w e r e m a d e us ing 4 m m (0.16 in.) d i a m e t e r E7010-HYP e lec t rodes and s tandard w e l d i n g c o n d i t i o n s and p rocedu re . T i m e lapses o f 10 m i n and 24 h w e r e s t u d i e d . Spec imens in d u p l i ­cate w e r e run fo r al l c o n d i t i o n s .

Results and Discussion

The resul ts o f t he tests are p resen ted

10 I 0 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0

Percent Cracking in Slot Weld Test

Fig. 10— Correlation between the actual girth-welded pipe in the shop and the laboratory Slot Weld Test (heat 492S1971)

in Tables 7 a n d 8. F rom these tests it is apparent tha t t h e results are q u i t e sen­si t ive t o t h e w i d t h o f t he test s lot . The sensi t iv i ty o f t he test t o s lot w i d t h was no t r educed w i t h a r e d u c t i o n in t he size of t he p la te and a c o n c o m i t a n t r e d u c t i o n in restra int level (Tab le 8).

It is seen f r o m Tab le 7 tha t in heat 492S1871, w h i c h p r o d u c e d extens ive c rack ing in the m a c h i n e d slot w e l d ­ab i l i t y test, t he fab r i ca ted slot w i t h a slot w i d t h o f 2.4 m m (0.09 in.) gave less severe c rack ing than the m a c h i n e d slot. This is t o be expec ted and is cons is ten t w i t h p rev ious s tud ies else­where , 1 " because t h e fab r i ca ted w e l d s are par t ia l p e n e t r a t i o n w e l d s w h i c h w o u l d p r o v i d e l o w e r restra int t han the so l id ends o f t he m a c h i n e d slot . H o w ­ever, it can also be seen f r o m Tab le 7 that in o the r heats e x h i b i t i n g o n l y m o d e r a t e a m o u n t s o f c rack ing , t he results on t he m a c h i n e d and fab r i ­ca ted spec imens w i t h slot w i d t h s o f 2.4 m m (0.09 in.) w e r e m u c h a l ike .

In any case, w h e r e t h e slot w i d t h in

Fig. 11-Effect of slot width on locus of cracking: A—no gap; B—2.4 mm gap; C— 3.2 mm gap. Nital etch

8 2 - s l M A R C H 1 9 8 0

Table 7-Effect of Slot Width

Heat

492S1871 B319 88284 490S2441

Mach

gap =

10 min

50% 30% 20% 2-3%

and

ned 2.4

Lapse Time on the Extent of Cracking

slot mm

24 h

80% 40% 20%

4-5%

Fabricated

gap

10 min

70% 30% 78% 18%

< 1.6 slot mm

24 h

83% 50% 95% 33%

Fabr

gap

10 min

70%

--—

cated = 1.6

slot mm

24 h

70%

--—

Fabricated gap = 2.4

10 min

< 25%

slot mm

24 h

40% Insufficient material

15% 1%

25% 5-8%

the fabricated slot was much less than 2.4 mm (0.09 in.), more severe cracking was encountered consistently, wi th most of the cracking occurring in the weld metal. This result is consistent wi th that obtained in Tekken Y-groove test'-" wherein severe weld metal cracking is reported when a slot width of 1 mm (0.04 in.) was used whi le the standard 2 mm (0.08 in.) slot width produced essentially HAZ cracking.

From the foregoing discussion it is apparent that fabricating methods are available which avoid the need for the machined slot in field testing. It has also been shown that the results of fabricated tests compare well wi th

those of the machined slot test for a range of steels with different cracking potentials when the slot w id th in the fabricated test is maintained at 2.4 mm (0.09 in.). One outcome of the study that seems quite important is that, no matter what the method of fabricating the test specimen, it must be carefully controlled so that a reproducible slot width of 2.4 mm (0.09 in.) results. Failure to control this dimension can lead to significant inaccuracies in the test.

Summary

The results of this investigation may

F«-90-H o u —a Tack Weld -

F i r s t Fabr i ca t ion Step

Tack weld with spacers in p l ace .

Tack weld with 2.4 mm space r s . Remove spacers before r e s t r a i n t weld. F ina l s l o t width < 1 . 66mr before t e s t weld was made.

Tack weld with 2.4 mm s p a c e r s . R e s t r a i n t weld with the t h r ee 2.4 mm spacers in p o s i t i o n . Center spacer removed before t e s t weld. F ina l s l o t width 1.6mm before t e s t weld was made .

I

be summarized as fol lows. 1. The slot weld test appears to be a

feasible shop test to determine the susceptibility of pipeline steels to hydrogen-induced cracking.

2. The test was shown to discrimi- . nate among various compositions of pipeline steels.

3. The benefit ot moderate preheat­ing in preventing hydrogen-induced cracking was demonstrated by the slot specimen.

4. The slot weld test permits estab­lishment of a schedule of preheat and time interval between root and hot pass welds to ensure welds free of cracking.

5. The slot weldabil ity test results were shown to correlate well wi th those of shop girth-welded pipes for a variety of welding condit ions (preheat and t ime lapse).

6. Methods of fabricating the slot weld test were shown to be available which could avoid the problems of applying the machined slot for field fabrication purposes. It was further shown that the results of fabricated test specimens compared well wi th those of the machined slot test speci­men for a range of steels wi th different cracking potentials when the slot width in the fabricated test was main­tained at 2.4 mm (0.09 in.) before depositing the test weld. Failure to control this dimension was shown to lead to inaccuracies in the test.

Acknowledgment

This investigation was made possi­ble by the support of the American Petroleum Institute and by American Iron and Steel Institute under the guid­ance of the WRC Weldabil i ty Commit­tee. The authors are grateful for their guidance and support.

Tack weld with 3.2 mm space r s . R e s t r a i n t weld over the space r s . No center spacer used. Final s l o t width 2.4 mm before t e s t weld was made.

Fig. 12—Slot weld specimen fabrication sequence

Table 8-Effect of Plate Size on Extent of Cracking for Heat 492S1871 (Plate Size = 200 mm x 125 mm)

Test condition

Machine slot (2.4 mm gap) Fabricated slot (1.6 mm gap) Fabricated slot (2.4 mm gap)

Cracking (24 h), %

15-20% 80% 20%

W E L D I N G RESEARCH SUPPLEMENT I 83-s

References

1. Stout, R. D., Vasudevan, R., and Pense, A. W. "A Field Weldabi l i ty Test for Pipeline Steels," Welding journal, 55(4), April 1976, Research SuppL, pp. 89-s to 94-s.

2. Winter ton, K., "Weldabi l i ty Prediction from Steel Composit ion to Avoid Heat-Affected Zone Cracking," Welding Journal, 39(6), |une 1961, Research SuppL, p. 253-s.

3. Ito, Y., and Bessyo, K., "Weldabi l i ty Formula for High Strength Steels," IIW Doc. No. IX-576-68.

4. Stout, R. D., and Doty, W. D., Weld­ability of Steels, 2nd Edit ion, Weld ing Research Council , New York, 1971.

5. Tanaka, T., et al., "Evaluation of Girth Welding for Arctic Grade Pipes," The Sumi­tomo Search No. 18, Nov. 1977, pp. 89-101.

6. Suzuki, H., "Cold Cracking and Its Prevention in Steel Weld ing," IIW Doc. No. IX-1074-78.

7. Fikkers, A. T., " Inf luence of External Restraint on Cold Cracking," Metal Con­struction and B.W.J., June 1974, p. 188.

8. Cordine, ]., "Weldabi l i ty of a Ni-Cu-Cb Line Pipe Steel," Welding journal, 56(6), June 1977, Research SuppL, pp. 179-s to 185-s.

9. Rothwell , A. B., "Weldabi l i ty of HSLA Structural Steels," Metal Progress, Vol. 111, No. 6, ]une 1977, pp. 43-50.

10. Gordine, )., "Weldabi l i ty of Some Arctic Grade Line Pipe Steels" Welding Journal, 56(7), July 1977, Research SuppL, pp. 201-s to 210-s.

11. Beckett, A. S., "Evaluation of API Field Weldabi l i ty Test," Columbia Gas Transmission Corporation Report, Nov. 29, 1977.

12. Stightz, R„ et al., "Lehigh Slot Weld Testing of X-60 Line Pipe Steels," Republic Steel Research Center Report, March 23, 1978.

13. Ueno, K., Shiga, A., and Tsuboi, |., "Field Weldabi l i ty Test for Pipeline Steels," Kawasaki Steel Corporation Report, Chiba, Japan, May 1977.

14. "Evaluation of API RP 5L7 Recom­mended Practice for Conduct ing Weldabi l i ­ty Tests on Linepipe," Report by Natural

G. C , "Evaluation of the Pipeline Steel Weldabi l i ty Research and Technology,

Gas Pipeline Co. of America, Dec. 22, 1977.

15. Schmid, New lehigh Test," Armco Feb. 3, 1978.

16. Smith, C , "The Evaluation of API Recommended Practice 5L7 for Conduct ing Weldabi l i ty Tests for Pipe Steels," Tennes­see Gas Pipeline Report, Nov. 14, 1978.

17. "Evaluation of API Recommended Practice 5L7 for Conducting Weldabi l i ty Tests on Pipe Steels," The Steel Company of Canada, Ltd., May 30, 1978.

18. Vasudevan, R., "Field Weldabi l i ty and Hydrogen Assisted Cracking in HSLA Pipe­line Steels Including The Arctic Grade," Ph.D. Dissertation, Lehigh University, 1979.

19 Test, 1978.

20. Campbell, W.P. , "Experiences wi th HAZ Cold Cracking Tests on a C-Mn Struc­tural Steel," Welding lournal, 55(4), May 1976, Research SuppL, pp. 135-s to 143-s.

"Evaluation of the Lehigh Slot-Weld U.S. Steel Corp. Bulletin, Dec. 11,

WRC Bulletin 255 December 1979

Experimental Investigation of Commercially Fabricated Ellipsoidal Heads Subjected to Internal Pressure

2:1

This WRC bulletin summarizes a series of progress reports on collapse tests of three commercially fabricated 2:1 ellipsoidal heads, conducted at the Foster Wheeler Development Corporation. Careful dimensional and material properties data were taken and three heads were pressurized to collapse. A wide range of stress and displacement data was obtained in both the elastic and inelastic regions. It appears that current computer computational techniques will accurately predict the elastic stress distributions for formed heads.

This summary report was prepared by a special task group of the subcommittee on Shells of the Pressure Vessel Research Committee of the Welding Research Council.

The price of WRC Bulletin 255 is $12.00 per copy plus $3.00 for postage and handling. Orders should be sent with payment to the Welding Research Council, 345 East 47th St., Room 801, New York, NY 10017.

WRC Bulletin 249 June 1979

Review of Analytical and Experimental Techniques for Improving Structural Dynamic Models by Paul Ibanez

The purpose of this paper is to review models for using experimental data to improve structural dynamic models for pressure vessels, piping systems, and their support and restraint systems. Laboratory models and scaling laws are discussed, followed by a summary of experimental results and potential bench mark cases on actual pressure vessel systems. Computer programs are also summarized, and an attempt is made to present a state-of-the-art summary of techniques for identification of structural dynamics models from experimental data.

Publication of this paper was sponsored by the subcommittee on Dynamic Analysis of Pressure Components of the Pressure Vessel Research Committee of the Welding Research Council.

The price of WRC Bulletin 249 is $11.50 per copy. Orders should be sent with payment to the Welding Research Council, 345 East 47th St., Room 801. New York, NY 10017.

84-s I M A R C H 1980