A Contribution of XPS and Electrochemistry to the Understanding of Hydrogen Diffusion in X60 Steel

Sustainable storage and transport of hydrogen are challenges in the transition to renewable energy sources. Hydrogen embrittlement (HE), caused by atomic hydrogen absorption and diffusion into steel, influences the mechanical properties of steel pipelines and reservoirs. This work focuses on the hydrogen diffusion on X60 pipeline steel using electrochemical measurements and X-ray photoelectron spectroscopy (XPS). The hydrogen permeation tests (HPT) were performed to estimate the effective hydrogen diffusion coefficient Deff and the subsurface hydrogen concentration C0 in cleaned and mechanically polished X60 steel. XPS analysis confirmed the presence of a 6 nm thick film of Fe (II) oxide, Fe (III) oxide, and Fe (III) oxyhydroxide. Mechanical polishing improved oxide layer uniformity, ensuring reproducible electrochemical behavior. The effective hydrogen diffusion coefficient Deff was determined for X60 steel using tlag and tb methods. It was found in the range from 2.0 (0.4) 10−10 m2/s to 2.9 (0.5) 10−10 m2/s. The subsurface hydrogen concentration, C0, was found to be 0.7 (0.1) ppm for X60 steel. The hydrogen diffusion in X60 steel depends on its bulk properties; it is unaffected by surface preparation methods, and it is confirmed to be lower than in high-carbon and other high-strength steels.