A model for the Hydrogen diffusion in Dual-Phase stainless steels for high-pressure applications

Hydrogen Embrittlement (HE) is a damaging phenomenon potentially affecting the integrity and the durability of stainless steels used in high-pressure applications. Knowledge of the local concentration of diffusible Hydrogen (H) and of the consequent mechanical properties’ degradation is fundamental for the structural assessment of the components. The operating loads This paper deals with the assessment of components made in Dual-Phase (DP) stainless steels under typical stress conditions in the presence of diffusible H. A coupled diffusion-structural model able to evaluate the H distribution is developed and presented. The main parameters driving H migration into this material are included i.e.: H concentration gradients, hydrostatic stress distribution, and plastic strain. The diffusion properties of the material were measured by specific permeation tests. Standard mechanical tests were performed to investigate the HE of the material in the presence of a uniform H distribution. Tests were carried out also on component-like specimens characterized by geometric discontinuities and therefore hydrostatic stress gradients. The model was employed to predict the local H concentration and assess the component strength by HE models published in the literature. The presented model can be used to improve the strength assessment of structural components under stress concentrations operating in environments generating H.