Microbiologically assisted stress corrosion cracking of X80 pipeline steel welded joint under cathodic protection

Stress corrosion cracking (SCC) poses a severe threat to the long-term integrity of high-strength steel pipelines, particularly under complex environments involving cathodic protection (CP) and microbial activity. This study investigates the synergistic effects of sulfate-reducing bacteria (SRB) and CP on the SCC behavior of welded joints in X80 pipeline steel. Slow strain rate tensile testing, electrochemical measurements, and hydrogen permeation analyses revealed that SRB markedly accelerate SCC by enhancing both hydrogen evolution and anodic dissolution. Fracture consistently occurred in the weld zone (WZ), attributed to its heterogeneous acicular ferrite–grain boundary ferrite microstructure, high-angle grain boundaries, and micrometer-scale Ti-rich inclusions acting as irreversible hydrogen traps. An exponential saturation relationship was established between the effective surface hydrogen concentration ( C s ) and SCC susceptibility. A safe CP potential range (−790 to −919 mV vs. SCE) was identified under sterile conditions; however, no viable protection window existed in SRB-active environments.