176 Y-Y Ma et aL/Engineering Failure Analysis 47(2015)162-177 where a is a factor related to the specific geometry in question, Ao the nominal stress range, a the crack length Based on former research 31. the two approaches that have mostly been used for assessing stress intensity factors for crack in weldments are numerical method and finite element method( FEm). It was proved 37 that the propagation lives of joints had much to do with the existence and the size of the LOP. The propagation live of joints with shorter size showed larger propagation lives, which was due to the fact that the crack had to propagate a longer distance in the weld metal. It showed that the intercept 'C varies with respect to LOP sizes. This provides a reasonable explanation to the pre-mature fail ure of the Cwp 5 Conclusions and recommendations 5.1. Conclusion 1. The LOPs in the weld induced by improper groove design decreased remarkably the strength and fatigue resistance performance of the weld joint, which was the most important cause to the fracture of the CWP. 2. Excessive content of ferrite in the weld joint, which should be induced by improper welding procedure decreased the mpact toughness and fatigue resistance performance, acting as another important cause to the failure 3. The base materials used in the flanges and cylindrical bodies of the CwP were qualified, indicating the failures cannot ascribed to the base material 4. With an unavoidable cycle load caused by operation of the pump the crack was originated on the intersection of the LOPs in the weld joints, propagating along the weld joint of the flange and eventually the final fracture of the flanges happened when it reached a certain length. 5. After the fracture of the flange, an unbalanced occurred on the whole shell, resulting in the other severe fractures. Thus the crack occurred on the base material belongs to a secondary fracture 5.2. Recommendations 1. Proper and strict procedure must be applied during the welding in order to obtain a full penetration joint and prevent the Lop. k preparation and Double-V preparation with proper parameters are recommended 2. Proper way such as enough cooling time, postweld heat treatment at 1050C should be applied to obtain a balanced f austenite/ferrite ratio. 3. Non-destructive method must be applied thoroughly after welding to ensure there is no fatal defect or flaw inside the weld joint. [1] Yang ZG, Gong Y, Yuan JZ Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: electrochemical rrosion. Mater Corros 2012: 63(1): 7-17 2] Gong Y, Yang ZG, Yuan JZ. Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: mechanical [4] Gong Y, Yang ZG. Corrosion evaluation of one dry desulfurization equipment-circulating fluidized bed boiler. Mater Des 2011: 32(1): 671-81 51 Gong Y, Cao J, Ji LN, Yang C, Yao C, Yang ZG, et al Assessment of creep rupture properties for dissimilar steels welded joints between T92 and HR3C. gue Fract Eng Mater Struct 2011: 34(2): 8 [6] Gong Y, Yang ZG, Yang FY Heat strength evaluation and microstructures observation of the welded joints of one China-made T91 steel. J Mater Eng Perform2012:21(71313-9 [7 Chen FJ. Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part I: corrosion and wear. Eng Fail Anal 2014: 37: 29-41 8 Chen F]. Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part ll erosion and cavitation corrosion. Eng Fail Anal 2014: 37: 42-52 [9] Gong Y, Yang ZG, Meng XH. Failure analysis of one peculiar"Yin-Yang corrosion morphology on heat exchanger tubes in purified terephthalic acid (PTA) dryer. Eng Fail Anal 2013: 31: 20 [10 lacoviello F, Boniardi M, La Vecchia GM. Fatigue crack propagation in austeno-ferritic duplex stainless steel 22 Cr 5 Ni. Int J Fatigue 1999: 21: 957-63 [111 Sieurin H, Sandstrom R Fracture toughness of a welded duplex stainless steel. Eng Fract Mech 2006: 73: 377-90 [12 Sieurin H, Sandstrom R Sigma phase precipitation in duplex stainless steel 2205. Mater Sci Eng A 2007: 444(1-2): 271-6. -Ta. Effect of selective dissolution on fatigue crack initiation in 2205 duplex stainless steel. Corros Sci 2007: 49(4): 1847-61 [14] Balbi M, Avalos M, El Bartali A, Alvarez-Armas L Microcrack growth and fatigue behavior of a duplex stainless steel. Int J Fatigue 2009: 31(11 2)2006-13. [15 Sahu JK, Krupp U, Christ H). Fatigue crack initiation behavior in embrittled austenitic-ferritic stainless steel. Int J Fatigue 2012: 45: 8-14. [16] Chiu PK, Weng KL Wang SH, Yang JR, Huang YS, Fang Jason Low-cycle fatigue-induced martensitic transformation in SAF 2205 duplex stainless stee [171 Young MC, Tsay LW, Shin C-S, Chan SLl The effect of short time post-weld heat treatment on the fatigue crack growth of 2205 duplex stainless steel welds. Int] Fatigue 2007: 29(12): 2155-62 pipe. USA: ASTM International: 2009 19 GBT 21833-2008, Austenitic- Ferritic(duplex) grade stainless steel seamless tubes and 20 Barsoum Z Residual stress analysis and fatigue of multi-pass welded tubular structures. Anal2008:15:863-74. [211 Kim S, Jin K Sung W. Nam S. Effect of lack of penetration on the fatigue strength of high th steel butt weld KSME J 1994: 8(2): 191-7where a is a factor related to the specific geometry in question, Dr the nominal stress range, a the crack length. Based on former research [31], the two approaches that have mostly been used for assessing stress intensity factors for crack in weldments are numerical method and finite element method (FEM). It was proved [37] that the propagation lives of joints had much to do with the existence and the size of the LOP. The propagation live of joints with shorter size showed larger propagation lives, which was due to the fact that the crack had to propagate a longer distance in the weld metal. It showed that the intercept ‘C’ varies with respect to LOP sizes. This provides a reasonable explanation to the pre-mature failure of the CWP. 5. Conclusions and recommendations 5.1. Conclusions 1. The LOPs in the weld induced by improper groove design decreased remarkably the strength and fatigue resistance performance of the weld joint, which was the most important cause to the fracture of the CWP. 2. Excessive content of ferrite in the weld joint, which should be induced by improper welding procedure, decreased the impact toughness and fatigue resistance performance, acting as another important cause to the failure. 3. The base materials used in the flanges and cylindrical bodies of the CWP were qualified, indicating the failures cannot be ascribed to the base material. 4. With an unavoidable cycle load caused by operation of the pump, the crack was originated on the intersection of the LOPs in the weld joints, propagating along the weld joint of the flange and eventually, the final fracture of the flanges happened when it reached a certain length. 5. After the fracture of the flange, an unbalanced occurred on the whole shell, resulting in the other severe fractures. Thus the crack occurred on the base material belongs to a secondary fracture. 5.2. Recommendations 1. Proper and strict procedure must be applied during the welding in order to obtain a full penetration joint and prevent the LOP. K preparation and Double-V preparation with proper parameters are recommended. 2. Proper way such as enough cooling time, postweld heat treatment at 1050 C should be applied to obtain a balanced f austenite/ferrite ratio. 3. Non-destructive method must be applied thoroughly after welding to ensure there is no fatal defect or flaw inside the weld joint. References [1] Yang ZG, Gong Y, Yuan JZ. Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: electrochemical corrosion. Mater Corros 2012;63(1):7–17. [2] Gong Y, Yang ZG, Yuan JZ. Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part II: mechanical degradation. Mater Corros 2012;63(1):18–28. [3] Gong Y, Yang C, Yao C, Yang ZG. Acidic/caustic alternating corrosion on carbon steel pipes in heat exchanger of ethylene plant. Mater Corros 2011;62(10):967–78. [4] Gong Y, Yang ZG. Corrosion evaluation of one dry desulfurization equipment-circulating fluidized bed boiler. Mater Des 2011;32(1):671–81. [5] Gong Y, Cao J, Ji LN, Yang C, Yao C, Yang ZG, et al. Assessment of creep rupture properties for dissimilar steels welded joints between T92 and HR3C. Fatigue Fract Eng Mater Struct 2011;34(2):83–96. [6] Gong Y, Yang ZG, Yang FY. Heat strength evaluation and microstructures observation of the welded joints of one China-made T91 steel. J Mater Eng Perform 2012;21(7):1313–9. [7] Chen FJ, Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part I: corrosion and wear. Eng Fail Anal 2014;37:29–41. [8] Chen FJ, Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part II: erosion and cavitation corrosion. Eng Fail Anal 2014;37:42–52. [9] Gong Y, Yang ZG, Meng XH. Failure analysis of one peculiar ‘Yin-Yang’ corrosion morphology on heat exchanger tubes in purified terephthalic acid (PTA) dryer. Eng Fail Anal 2013;31:203–10. [10] Iacoviello F, Boniardi M, La Vecchia GM. Fatigue crack propagation in austeno–ferritic duplex stainless steel 22 Cr 5 Ni. Int J Fatigue 1999;21:957–63. [11] Sieurin H, Sandström R. Fracture toughness of a welded duplex stainless steel. Eng Fract Mech 2006;73:377–90. [12] Sieurin H, Sandström R. Sigma phase precipitation in duplex stainless steel 2205. Mater Sci Eng A 2007;444(1–2):271–6. [13] Lo I-Hsuang, Tsai Wen-Ta. Effect of selective dissolution on fatigue crack initiation in 2205 duplex stainless steel. Corros Sci 2007;49(4):1847–61. [14] Balbi M, Avalos M, El Bartali A, Alvarez-Armas I. Microcrack growth and fatigue behavior of a duplex stainless steel. Int J Fatigue 2009;31(11– 12):2006–13. [15] Sahu JK, Krupp U, Christ HJ. Fatigue crack initiation behavior in embrittled austenitic–ferritic stainless steel. Int J Fatigue 2012;45:8–14. [16] Chiu PK, Weng KL, Wang SH, Yang JR, Huang YS, Fang Jason. Low-cycle fatigue-induced martensitic transformation in SAF 2205 duplex stainless steel. Mater Sci Eng A 2005;398(1–2):349–59. [17] Young MC, Tsay LW, Shin C-S, Chan SLI. The effect of short time post-weld heat treatment on the fatigue crack growth of 2205 duplex stainless steel welds. Int J Fatigue 2007;29(12):2155–62. [18] ASTM A790/A790M-09. Standard specification for seamless and welded ferritic/austenitic stainless steel pipe. USA: ASTM International; 2009. [19] GB/T 21833-2008, Austenitic – Ferritic (duplex) grade stainless steel seamless tubes and pipes (in Chinese). [20] Barsoum Z. Residual stress analysis and fatigue of multi-pass welded tubular structures. Eng Fail Anal 2008;15:863–74. [21] Kim S, Jin K, Sung W, Nam S. Effect of lack of penetration on the fatigue strength of high strength steel butt weld. KSME J 1994;8(2):191–7. 176 Y.-Y. Ma et al. / Engineering Failure Analysis 47 (2015) 162–177