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

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. © 2024 Chinese Mechanical Engineering Society. All rights reserved.