Study of the Effect of Sulphide Stress Corrosion on the Load Bearing Capability of API 5L Grade B Steel used in Petroleum Pipelines

The Phenomenon of Sulfide Stress Corrosion (SSC) can result in catastrophic failures in pressurized equipment and piping leading to extensive damages, injuries and possible fatalities. SSC, a major degradation process in metals, is commonly associated with the petroleum industry where a high concentration of H2S is involved. For pipelines in the petroleum and natural gas industries, API 5L Grade B Steel type is extensively used. This research focuses on developing a correlation between load at fracture and time period exposed to a constant H2S concentration under a constant load. Furthermore, the mechanism of growing the depth of corrosion is studied in terms of microstructural analysis. Correlations of depth of corrosion versus exposure time and load at fracture versus exposure time have been developed. It was concluded that variation of the load at fracture with the depth of corrosion closely fits the proposed model within the 55μm to 80μm depth range. Additionally, the progress of developing micro cracks towards the unaffected metal has significantly contributed to the drastic reduction in load bearing capability beyond the depth of corrosion around 55μm. The results showed that the combined effect of developing of microcracks and formation of sulfides within the corrosion layer and base metal has led to the ultimate brittle fracture of specimens.