Effects of multiple welding thermal cycles on hydrogen permeation parameters of X80 steel

Abstract Hydrogen permeation tests were conducted in 1.2 MPa H2 on welding thermal simulated specimens to determine the hydrogen permeation parameters in each subzone of the girth welded joints. Optical microscope, electron back-scattered diffraction, and X-ray diffraction were applied to analyze the corresponding microstructure changes. The results show that the hydrogen diffusion coefficient D is mainly determined by the final heat-treated peak temperature, and the key microstructural affecting factors of hydrogen permeation will change with this temperature. The order of D from high to low is acicular ferrite, granular bainite, lath bainite, polygonal ferrite, and M-A constituent.