Developing a model to predict the propagation of sulphide stress corrosion of steel used for petroleum pipelines

Sulphide stress corrosion (SSC) is an abundant type of corrosion in petroleum refineries. Steel pipes in petroleum refineries are influenced by the synergistic effect of tensile stress/pressure and high H2S concentrations in different environments. This paper focuses on the prediction of the propagation of depth of SSC in API 5L Grade B steel as a function of pH value, applied load, and time duration. The model has been established based on the experimental values of the depth of SSC under different predetermined test environmental conditions kept within the pH value of 2.7-3.5, an applied load of 400-800 N, and a time duration of 15-45 days. Further, the model was validated by another data set obtained for the depth of corrosion within the same aforementioned ranges of parameters. All the laboratory experiments were conducted in accordance with ANSI/NACE TM0177-2016 standard test methods. In addition, this paper discusses the microstructural observations of specimens kept under the aforementioned test environmental conditions. The scanning electron microscope (SEM) images of cross-sections of corroded specimens showed that crack initiation occurred after 15 days under all different test environmental conditions. Further, crack propagation occurred transversely, developing branches through the cross section until 30 days of time duration and the behaviour of the propagation of the crack was completely changed at 45 days of time duration.