焊接热输入对X65管道粗晶热影响区应力腐蚀开裂行为的影响

Effect of Welding Heat Input on Stress Corrosion Cracking Behavior in Coarse Grain Heat Affected Zone of X65 Pipeline

X65管道粗晶热影响区(Coarse grain heat affected zone,CGHAZ)在海底服役过程中易出现硫化物应力腐蚀开裂(Sulfide stress corrosion cracking,SSCC)现象,现阶段研究大多集中在应力腐蚀的产生以及影响因素的理论层面,很少提到通过优化传统焊接参数来获得抗SSCC能力更强的X65管线钢。由此基于传统X65钢的焊接工艺,开发一种低热输入的优化X65焊接工艺,并通过微观组织分析、慢应变速率拉伸试验及断口分析等方式对比研究两种工艺对CGHAZ的SSCC敏感性的影响。试验结果表明,传统工艺制造的X65管线钢盖面、打底部位的CGHAZ应力腐蚀敏感性R分别为56.51、59.50,其微观组织主要为M-A组元和粒状贝氏体(Granular bainite,GB),两者的存在会促进裂纹的萌生或扩展,由此导致X65钢的SSCC敏感性较高;优化工艺制造的X65钢盖面、打底部位的CGHAZ应力腐蚀敏感性R分别为35.78、30.31,其主要组织为针状铁素体(Acicular ferrite,AF),且针状交织分布的AF对裂纹的扩展有着有效地阻止作用。由此,提出一种低热输入高SSCC抗性的X65焊接工艺,并从微观组织、裂纹扩展等方面阐述了优化工艺提高X65管线钢抗SSCC性能的原因。

X65 pipeline coarse grain heat affected zone(CGHAZ)is prone to sulfide stress corrosion cracking(SSCC)phenomenon during seabed service,and most of the current research focuses on the theoretical level of stress corrosion generation and influencing factors,and rarely mentions X65 pipeline steel with stronger SSCC resistance by optimizing traditional welding parameters.Based on the welding process of traditional X65 steel,an optimized X65 welding process with low heat input is developed,and the effects of the two processes on the SSCC sensitivity of CGHAZ are compared and studied by microstructure analysis,slow strain rate tensile test and fracture analysis.The test results show that the stress corrosion sensitivity R of the cover surface and bottom of the X65 pipeline steel manufactured by traditional process is 56.51 and 59.50,respectively,and its microstructure is mainly M-A component and granular bainite(GB),the presence of which will promote the initiation or expansion of cracks,resulting in high SSCC sensitivity of X65 steel.The stress corrosion sensitivity R of X65 steel cover surface and bottom CGHAZ in the optimized process is 35.78 and 30.31,respectively,and the main structure is needle-like ferrite,and the AF with needle-like interwoven distribution had an effective inhibitory effect on crack propagation.Therefore,a welding process of X65 with low heat input and high SSCC resistance is proposed,and the reasons why the optimized process can improve the SSCC resistance of X65 pipeline steel are explained from the aspects of microstructure and crack propagation.