Stress Corrosion Cracking Mechanism of UNS S31803 Duplex Stainless Steel under High H2S-CO2 Pressure with High Cl- Content

Ding, Jinhui (University of Science and Technology Beijing) | Lu, Minxu (University of Science and Technology Beijing) | Zhang, Lei (University of Science and Technology Beijing) | Li, Dapeng (University of Science and Technology Beijing) | Yu, Yong (China Petroleum Engineering Company, Limited)



The stress corrosion cracking (SCC) behavior of duplex stainless steel (DSS) in H2S-C1- environment has been discussed for a long time. However, the high H2S-CO2 pressure and the high Cl- content can coordinate to cause severe pitting or SCC of DSS. There has been limited information on the mechanism of SCC of DSS under high H2S-CO2 pressure with high Cl- content. In this paper, SCC of UNS S31803 DSS was investigated under different H2S-CO2 pressures (300 kPa H2S + 200 kPa CO2, 600 kPa H2S + 400 kPa CO2, 900 kPa H2S + 600 kPa CO2) with 150,000 ppm Cl- at 60 °C. Four-point bend beam test method and scanning electron microscopy analysis were combined to investigate the SCC mechanism of DSS. The effect of high H2S-CO2 pressure on SCC mechanism was discussed. The results indicated that under lower H2S-CO2 pressure, cracks initiated and propagated at pitting areas which were caused by anodic dissolution mechanism. Under 900 kPa H2S + 600 kPa CO2, except the pitting assisted cracking areas, there also existed some hydrogen stress cracking at crack terminals. The higher H2S-CO2 pressure can facilitate both hydrogen embrittlement and anodic dissolution.