Effect of hydrogen trap density on efficiency of irreversible traps in a line-pipe steel

Hydrogen embrittlement (HE) presents a significant challenge for the enduring reliability of high-strength steels employed in pipelines and energy infrastructure. This challenge arises from the intricate interactions among microstructural traps that control hydrogen entry, storage, and release. Although the phenomenon of hydrogen trapping is well-explored, the significance of trap competition and the dynamic movement of hydrogen between reversible and irreversible traps is only recently acknowledged as a crucial factor influencing susceptibility to embrittlement. In this study, we examined hydrogen trap competition through thermal desorption spectroscopy (TDS) and in situ transmission electron microscope (TEM) experiments. Two microstructures from line-pipe X70 grade steel with differing grain boundary areas were produced, with one of the steels exhibiting a relatively higher percentage (∼64%) of high-angle grain boundaries (HAGBs). The local accumulation of hydrogen at HAGBs seemed to result in a reduction of the effective hydrogen diffusion coefficient by 40%, from 1.6 × 10 -11 to 0.92 × 10 -11 m² s -1 . This likely diminished the likelihood of hydrogen engaging with the precipitates within the grain matrix. Consequently, a 50% reduction in trapped hydrogen at irreversible sites was observed.