Sensitivity to hydrogen induced cracking, and corrosion performance of an X65MS pipeline steel in H2S containing environment

This study investigates the microstructure and hydrogen sulfide (H 2 S) corrosion resistance of X65MS acid-resistant pipeline steel, focusing on its susceptibility to hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSCC). The steel, characterized by an acicular ferrite (AF) microstructure, was developed using thermomechanical controlled processing (TMCP) to enhance its resistance to acidic, H 2 S-rich environments. The AF microstructure, composed of polygonal ferrite, bainitic ferrite, and dispersed M/A islands, exhibits superior resistance to HIC due to its high dislocation density and randomly oriented grain boundaries, which effectively trap hydrogen atoms and mitigate crack propagation. Mechanical tests confirmed that the steel meets API Spec 5L standards, with high impact toughness and low susceptibility to HIC and SSCC. Electrochemical analyses in simulated H 2 S environments revealed that the addition of sodium thiosulfate (S 2 O 3 2 − ) initially accelerates corrosion but forms a protective iron sulfide film at higher concentrations, reducing the corrosion rate. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses highlighted the steel’s fine-grained structure and uniform distribution of precipitates, which further enhance its corrosion resistance. The study concludes that the AF microstructure, combined with micro-alloying elements such as Nb, Ti, and Mo, significantly improves the steel’s resistance to H 2 S-induced corrosion, making it suitable for harsh oil and gas transportation environments. These findings provide valuable insights for the development of high-strength, corrosion-resistant pipeline steels.