Study of the Resistance of Low-Alloy Pipe Steels to Hydrogen-Induced Cracking

The oil and gas industry needs seamless steel pipes resistant to hydrogen-induced cracking, driven by the development of increasingly complex, deep, and high-pressure fields, oil production with high hydrogen sulfide content, and the growing number of hydrogen-based decarbonization projects. The aim of the work was to investigate the mechanism of formation of non-metallic inclusions in 13ChFA-grade steel that are potentially significant for HIC pipe steel, a low-alloy steel similar to AISI 5115, and to develop steelmaking-process modifications that improve its resistance to hydrogen-induced cracking. Non-metallic inclusions in seamless-pipe samples were examined by micro-X-ray spectral analysis across 11 laboratory protocols comprising 213 spectra. Based on the identified inclusion-formation mechanism, process modifications were developed and tested in five pilot heats at the electric-arc-furnace, ladle-furnace, and vacuum-degassing stages; the effect was verified on samples from serial production. Resistance to hydrogen-induced cracking was evaluated according to the NACE TM0284-2011 standard, and inclusion content according to the GOST 1778 standard. In 8 of the 11 cases of defects examined (≈73%), the recorded steelmaking defects were associated with two types of inclusions potentially significant for HIC: endogenous conglomerates of magnesian spinel, calcium aluminate, and sulfide phases (about 45%), and manganese–iron silicate films (about 27%); the remaining 27% were exogenous slag inclusions. Reducing the oxygen content before tapping, increasing the addition of lime and fluorspar, limiting the metal residence time in the ladle, and controlling the calcium-to-sulfur ratio during secondary treatment yielded pilot heats with zero crack sensitivity, crack length, and crack thickness ratios, while inclusion content complied with the steel-cleanliness standard. In a series of five trial heats—conducted without a parallel control group—a consistent relationship was observed between controlled ladle treatment parameters, the type and quantity of inclusions potentially significant for HIC, and a standardized hydrogen-induced cracking resistance index. The resulting set of process modifications, tested under industrial conditions across five heats, represents a practical approach to enhancing the resistance of low-alloy pipe steels to hydrogen cracking.