Hydrogen permeation and embrittlement susceptibility of X80 welded joint under high-pressure coal gas environment

•An electrochemical hydrogen permeation device was designed for high pressure gases.•The sensitivity of CGHAZ to HE is the highest in welded joints.•HE sensitivity depends on material microstructure and hydrogen permeation behavior.

Hydrogen permeation and slow strain rate tests in a high-pressure hydrogen-containing coal gas, combined with microstructural analysis, were conducted on X80 base metal, weld metal, and coarse-grained heat-affected zone (CGHAZ). Variation in the calculated diffusivity from high to low was in the following sequence: CGHAZ, weld metal, and base metal. This result was contrary to those of sub-surface hydrogen concentration and hydrogen embrittlement susceptibility. Hydrogen permeation in CGHAZ decreased the cross-sectional shrinkage by 34.56%, which indicates susceptibility to hydrogen embrittlement. The co-effects of microstructure, hydrogen diffusivity, and concentration were the main factors that influenced hydrogen embrittlement susceptibility.