Effect of nickel on the hydrogen diffusion, trapping and embrittlement properties of tempered ferritic-martensitic dual-phase low alloy steels

Hydrogen embrittlement (HE) poses a significant threat to hydrogen pipelines, which are regulated by ASME B31.12 standard specifications. The standard imposes a limit of 0.5 wt% nickel content in low alloy steels (LAS) to reduce HE risk, potentially excluding numerous modern high-performance steels from hydrogen applications. This study quantified the fundamental impact of nickel content on hydrogen diffusion mechanisms, trapping behavior, and overall HE resistance using tempered dual-phase ferritic-martensitic LAS. Notably, increasing the Ni content to 3 wt% resulted in a 1.74-fold decrease in the apparent diffusion coefficient and a 2.4-fold increase in hydrogen trapping. Crucially, increasing Ni content demonstrated no detrimental effect on HE resistance, as evaluated through in-situ slow strain rate testing. These findings provide valuable insights for optimizing LAS compositions with up to 3 wt% Ni for enhanced performance in hydrogen service applications, suggesting that the conservative limits in the current standards could be strategically revisited to accommodate advanced steel grades. • Ni additions reduce H diffusion coefficient by 1.74-fold via grain refinement. • Ni increases H trapping content 2.4-fold through higher grain boundary density. • 3 wt% Ni does not affect hydrogen embrittlement resistance in dual-phase LAS steels.