Abstract: The electrochemical hydrogen permeation dynamic behavior of X120 pipeline steel was investigated by Davanathan-Stachursky dual cell system. Electrochemical hydrogen charging method was used for prefabricating micro-cracks, and scanning electron microscope(SEM) was employed to observe inclusions and hydrogen induced cracking in X120 pipeline steel. The results demonstrate that the saturated anode current I∞, hydrogen flux J∞ and hydrogen effective diffusion coefficient Deff increase with the increase of charging current density. The effect of inclusions in the steel on the crack initiation depends on their chemical compositions. There are three kinds of inclusions, such as Al/Mn contained sulfide/oxide, Ti/Nb contained nitride complex and Ca-Al-O-S mixed inclusions in the experimental X120 pipeline steel. Hydrogen induced cracking is initiated easily at the sites of Al/Mn contained inclusions, the cracks nucleate and then grow along with the rolling direction.

Key words: X120 pipeline steel, hydrogen permeation dynamics, hydrogen induced cracking, inclusions