Hydrogen-Induced Crack Growth Rate in Steel Plates Exposed to Sour Environments

A mathematical model was proposed for determining the crack growth rate of hydrogen-induced cracking (HIC) in steel plates exposed to a sour gas. The model assumes that the extension of an embedded circular crack results from accumulation of internal hydrogen pressure that produces a rise of the stress intensity factor in excess of the plane strain fracture toughness of the steel with dissolved hydrogen. Upon crack extension, the volume of the crack cavity increases, and the pressure drops, causing the crack to arrest. As the cavity is filled again with hydrogen, the process is repeated. HIC experiments were conducted on API 5L-X52 steel plates, using ultrasonic inspection to measure crack sizes. Data from inspected sour gas pipelines were gathered and compared to the predicted crack growth rates. The model showed reasonable agreement with experimental results, which corresponded to the first stages of HIC growth. It failed to approximate values for large crack lengths found in pipelines after long exposure to sour gas. This suggested either that there were important crack delay processes or that the cracking criterion changed as the crack grew. These delay processes were related to the effect of metallurgical variables.