Abstract: X70MS pipeline steel is mainly used to transport oil and natural gas containing H₂S and other acidic media. Due to its special service environment, pipeline steel is required to have very good HIC resistance. In order to reduce the HIC sensitivity of X70MS pipeline steel and improve its service safety, the HIC resistance performance of X70MS pipeline steel was studied using NACE TM 02842016 hydrogen-induced cracking standard experimental method. The results show that the microstructure of X70MS pipeline steel is ferrite, bainite and M/A island. In the HIC test, each index parameter of cracks meets the requirements of the domestic evaluation standard of X70 pipeline steel for West-East Gas Pipeline Project，and has good resistance to HIC. HIC cracks are caused by the segregation of Al₂O₃ inclusions and C elements in the slab into the steel plate to form a large M/A island carbon-rich structure, the coupling effect between Al₂O₃ inclusions and M/A island structure will aggravate the deterioration of HIC resistance of X70MS pipeline steel, and the number, distribution and size of M/A islands are important factors affecting the HIC resistance of X70MS pipeline steel.

Key words: X70MS steel, HIC, inclusions, segregation, M/A island