Fractal effect of hydrogen induced crack in high sulfur gathering pipeline and calculation of its propagation rate

Hydrogen induced cracking (HIC) is one of the main failure modes of high-sulfur gas field gathering pipeline network and long-distance pipeline steel. In order to clarify the mechanism and process of pipeline HIC, the cracking mode was studied. The change rule of mass concentration of hydrogen during the propagation of metal crack tip was analyzed, the dynamic model of hydrogen induced crack was corrected with consideration giving to fractal effect, and the straight crack-shear band fractal model was proposed for the propagation of hydrogen induced crack. On the basis of Gerberich's research on HIC, the shape of the fracture process zone and the crack propagation length were combined based on the hydrogenation of crack tip and the coupling factors existing during the crack propagation, the expression of the fractal rate in each stage of the hydrogen induced crack propagation was constructed, and a more reasonable mathematical model of HIC based on the fractal effect was obtained. Taking the natural gas pipeline made of 16Mn and 20 steel as example, the propagation rate of hydrogen induced crack at the base metal and the weld joint was calculated respectively, and the H₂S resistance of the two materials was obtained by comparison. Therefore, the research results have certain guidance significance for the selection of high-sulfur pipeline materials.