Effect of tensile stress on the hydrogen permeation of MS X65 pipeline steel under sulfide films

Abstract

The effect of the tensile stress on the hydrogen permeation of MS X65 pipeline with sulfide films was investigated through measuring the steady-state hydrogen permeation current (I∞), permeability (J∞L) and apparent diffusivity (Dapp) and quantitatively analysing the hydrogen-permeable resistance factor (HPRF) of single tensile stress HPRF (stress), single sulfide film HPRF (film) and the two together HPRF (stress-film). The results indicated that J∞L and sub-surface hydrogen concentration (co) greatly increase and that Dapp decreases as the elastic stress increases. When applying plastic stress, J∞L and Dapp all reduce, while co continues to increase without the film but decreases with the film. While single tensile stress can promote hydrogen permeation, with the sulfide film, the value of HPRE (stress-film) is not a simple addition of the value of the HPRE (stress) and the HPRE (film), and the interaction results in the blocking effect of hydrogen permeation. The surface morphology of the sulfide films changes caused by tensile stress should be responsible for the HPRE (stress-film) reducing as tensile stress increases but increasing with plastic tensile stress.