Weldability and stress corrosion resistance of WDL series steel with lowsusceptibility to weld cracking

Xiao Chen

National Enterprise Technology Centre of Wuhan Iron and Steel (Group) Co., 28 Yejin Road, Qingshan District Wuhan, Hubei 430080People’s Republic of China

Received 1 September 1998; accepted 24 September 1998

Abstract

In this article the weldability, stress corrosion resistance and application of low susceptibility to crack 07MnCrMoV series steel (WDL)were researched; the results show that WDL steel has excellent weldability and superior stress corrosion resistance.q 1999 Published byElsevier Science Ltd. All rights reserved.

Keywords:Low susceptibility to weld crack; Stress corrosion; Weldability; Large spherical vessels

1. Introduction

WDL series steel is a new generation of High StrengthLow Alloy steel in the world, it has high strength, goodductility and excellent weldability. The plates of thicknesst # 50 mm do not lead to cold weld cracking withoutpreheating, or with just slight preheating before welding.Plates of thicknesst # 38 mm do not need stress reliefannealing (SR) after welding. WDL steel is an ideal materialfor the manufacture of large scale pressure vessels (espe-cially room-temperature and low-temperature spherical gasholders), hydraulic power station pressure pipes, spiralcases, offshore petroleum platforms, large span bridgesand heavy engineering machinery used under severe condi-tions.

2. Composition and mechanical properties of WDL steels[1]

These are summarised in Table 1 and Table 2.

3. Weldability research

3.1. Cold crack susceptibility test

Maximum hardness distribution of welded heat affectzone (HAZ) are shown in Fig. 1. Y-Slit restraint crackingtest results are shown in Table 3. The results of maximumhardness distribution and Y-slit restraint cracking test

indicate that WDL series steel has excellent weldabilitywith very low cold weld susceptibility.

3.2. Welding process estimation test

The test plates were not preheated before welding, theinterpass temperature was 1508C–2008C. The SR tempera-ture was 5708C ^ 158C after welding giving the results of2 408C V-Charpy toughness of weld metal and HAZ asshown in Table 4.

3.3. Series temperature impact test of HAZ

The experiment results of WDL series steel are shown inTable 5.

3.4. NDT of welded joint

Nil-ductility transition temperature of different weldjoints and HAZ conditions are revealed in Table 6.

Through experiments of welding processes, V-charpyimpact and NDT Temperature of welding and HAZ, wecan draw a conclusion that WDL series steel has superiorweldability.

4. Experiment of stress corrosion resistance

Spherical holders and pressure vessels may be filled withH2S solution, which tend to cause stress corrosion cracking(SCC). High strength steels (sb # 570 MPa) are very sensi-ble to wet H2S stress corrosion. When the wet H2S density is

International Journal of Pressure Vessels and Piping 76 (1999) 19–22

0308-0161/99/$ - see front matterq 1999 Published by Elsevier Science Ltd. All rights reserved.PII: S0308-0161(98)00111-2

# 0.005%, the steels do not need to be SR annealed butwhen the density is 0.005%–0.010%, the steels must be SRannealed, when it is. 0.01%, such steels should not beused. To determine whether WDL series steels can be usedas pressure vessels which can be filled with H2S solution, wedid systematic H2S stress corrosion resistance tests accord-ing to the related national and domestic standards includingConstant Stress Tension Test; Simple Supporting BeamTest; Constant Displacement WOL Test. The results areshown in Table 7.

The results indicate that the anti-H2S stress corrosionresistance of base metal, welded joint and corresponding

forge pieces of WDL series steel are all up to standard orsuperior to those of WEL-TEN62CFS.

5. Application

5.1. Large spherical holders

Sixty two room-temperature and low-temperature sphe-rical gas holders were made, one of these, a 5000 m3 low-temperature ethylene holder that was put into use in Daqingcity (China) by the Labor Ministry in Nov. 1993, is the first

X. Chen / International Journal of Pressure Vessels and Piping 76 (1999) 19–2220

Table 1Chemical Composition (%)

Grade C Si Mn P S Ni Cr Mo V B Pcma

WDL610D # 0.09 0.15–0.40 1.20–1.60 # 0.030 # 0.020 # 0.30 0.10–0.30 0.10–0.30 0.02–0.06 # 0.0030 # 0.20WDL610E # 0.09 0.15–0.40 1.20–1.60 # 0.025 # 0.015 0.20–0.50 0.10–0.30 0.10–0.30 0.02–0.06# 0.0030 # 0.21WDL570D # 0.11 0.15–0.40 1.00–1.60 # 0.030 # 0.020 # 0.30 # 0.30 # 0.30 0.02–0.06 # 0.0030 —WDL570E # 0.11 0.15–0.40 1.00–1.60 # 0.030 # 0.020 # 0.30 # 0.30 # 0.30 0.02–0.06 # 0.0030 —

a Pcm� C 1 Si/30 1 Mn/20 1 Cu/201 Cr/201 Ni/60 1 Mo/15 1 V/10 1 5B(%).

Table 2Mechanical properties

Grade Plate condition Direction location Thickness (mm) YP (MPa) TS (MPa)d5 (%) Impact test (8C) Akv(J) Bend testb � 2a,1808

WDL610D Q.T T.t/4 16–50 $ 490 610–740 $ 17 2 20 $ 47 d � 3aWDL610E Q.T T.t/4 16–50 $ 490 610–740 $ 17 2 40 $ 47 d � 3aWDL570D Q.T T.t/4 16–50 $ 440 570–720 $ 17 2 20 $ 47 d � 3aWDL570E Q.T T.t/4 16–50 $ 440 570–720 $ 17 2 40 $ 47 d � 3a

Table 3Y-slit restraint cracking test results

Grade Thickness (mm) Pcmb RT Preheat 508C Deposited [H]ml/100gSection % Root % Section % Root %

WDL610D 24 0.20 0 0 — — # 1.5036 0.20 0 0 0 0 1.4336 0.20 1.56 0 0 0 1.7936 0.18 0 0 0 0 1.46WDL610E 44 0.199 0 8.75 0 1.04

a Pcm� C 1 Si/30 1 (Mn 1 Cu 1 Cr)/201 Ni/60 1 Mo/15 1 V/10 1 5B

Table 42 408C impact test results of different welding position

Weld position Plate condition Heat input KJ/cm 2 408C VE (J)Weld HAZ

Downhand Welded 17–20 101 126 110 177 154 169Downhand Welded1 SR 17–20 128 160 144 128 184 188Horizontal Welded1 SR 15–17 90 90 132 — — —Vertical Welded 29–34 68 85 120 180 170 162Vertical Welded1 SR 29–34 87 60 76 119 112 154Overhead Welded 30–33 88 60 64 56 56 64Overhead Welded1 SR 30–33 47 39 47 41 63 80

successful application in the world. It was inspected inSeptember 1996, everything is going smoothly.

5.2. Breech pipes and pressure steel tube of hydraulic powerstation

The largest four-way pipe without girder in China wasmade for Xinjiang Kashi hydropower station. It was put intouse in December 1992, up to now, it is running safely with-out any problems. Large breech pipes were made for theSuojinshan (Wufeng Hubei, China) and Xiang hydroplants

located on the border of Yunnan and Guizhou provinces;they are warmly welcomed by the users.

5.3. Heavy engineering machinery under severe conditions

One hundred and eight tons electrically operated Pumptruck and 10 m3 excavators are significant examples of tech-nological equipment with yearly production of ten milliontons. They were usually dependent on import; from 1986they were made with WDL steel. They were used inNeimeng Baiyunebo iron ore, Benxi Nanfen iron ore,Sougang water-factory iron ore, Fuxun coal ore, where in

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Table 5V-Notch Charpy impact test results at series temperature of welded joint HAZ (44 mm-thick steel plate)

Specimen condition Experimental temperature (8C) Impact test Akv J. Side expansion (mm) Crystal section rate (%)

Welded RT 208 199 182 2.13 2.10 2.08 0 0 00 236 156 236 2.21 1.73 2.19 0 12 02 20 172 202 199 1.84 2.00 2.01 9 5 02 40 177 154 169 1.82 1.65 1.71 23 48 322 50 189 172 96 1.93 1.78 1.12 34 39 502 60 72 115 104 0.91 1.43 1.36 62 55 592 80 141 42 168 1.39 0.53 1.46 42 63 38

Welding 1 570^158C × 2 h SRannealing

RT 208 212 226 1.91 2.10 2.01 0 0 0

0 215 220 200 2.12 2.15 1.98 0 4 02 20 208 182 164 1.99 1.88 1.79 6 18 262 40 184 188 122 1.83 1.87 1.67 29 31 472 50 200 180 56 1.95 1.81 0.71 24 39 462 60 48 158 168 0.57 1.60 1.74 68 49 432 80 41 64 52 0.54 0.86 0.63 79 71 77

Table 6NDT results of welded joint and HAZ

Thickness (mm) V-Notch position Groove type Specimen condition Specimen type Impact energy J NDT8C

38 Welded Metal HAZ Asymmetric double V Welded P-2 400–450 2 60Welded1 SR P-2 400–450 2 60Welded P-2 400–450 2 35Welded1 SR P-2 400–450 2 35

44 Welded metal Asymmelxic double V Welded P-2 400–450 2 55Welded1 SR P-2 400–450 2 45Welded1 2-SR P-2 400–450 2 45

Table 7Stress corrosion resistance results in H2S

Position Specimen Grade Thickness (mm) YP MPa s th/s s Sc MPa KI scc mm1/2

Base Metal WDL610D 24 550 — 1360 3.0WDL610D 36 590 0.69 965 2.5WDL610D 38 570 0.59 — —WDL610E 44 550 0.87 1850 —WEL-TEN62CF 36 580 0.36 — 2.4

Weld Metal WDL610D 36 — 0.61 — 2.9WDL610D 38 — — 1170 —WEL-TEN62CF 36 — 0.69 940 2.6

Forge 08MnNiCrMo VD — 540 0.54 — 2.8Standard $ 0.45 $ 830 $ 1.5

winter the temperature is always2 30– 2 488C, whichrequires the WDL steel because of its excellent low-temperature toughness.

A new WDL series steel was produced for more than 28thousand tons; because of the comprehensive properties thewelding process for using the steel was simplified and the

manufacture period was shortened as well, allowing thewelders’ working conditions to be improved. The qualityand reliability of the large steel structure was enhanced sothat the economic and social benefits were obvious.

6. Conclusion

1. WDL series steel was widely applied in large room-temperature and low-temperature spherical holders andother pressure vessels, hydraulic power station pressurepipes, heavy engineering machinery used under severeconditions. Great economic and social profit was madeand a great contribution was made to domestic emphasistechnological equipment.

2. The weldability and stress corrosion resistance aredescribed systematically. A great deal of engineering tech-nical data provides scientific guidance for its widespreadapplication in the engineering zone.

References

[1] Chen X. Iron & Steel 1998;31(12):30–44.

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Fig. 1. Welded HAZ maximum hardness distribution of WDL610E steel(44 mm-thick steel plate 20 mm-thick specimen).