HYDROGEN-INDUCED CRACK-GROWTH RATE IN STEEL PLATES EXPOSED TO SOUR ENVIRONMENTS

A mathematical model was proposed for determining the crack growth rat e of hydrogen-induced cracking (HIC) in steel plates exposed to a sour gets. The model assumes that the extension of an embedded circular cr ack results from accumulation of internal hydrogen pressure that produ ces a rise of the stress intensity factor in excess of the plane strai n 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 compar ed to the predicted crack growth rates. The model showed reasonable ag reement with experimental results, which corresponded to the first sta ges of HIC growth. It failed to approximate values for large crack len gths found in pipelines after long exposure to sour gas. This suggeste d either that there were important crack delay processes or that the c racking criterion changed as the crack grew. These delay processes wer e related to the effect of metallurgical variables.