Pit Propagation of Carbon Steel in Sour Conditions

摘要

Pitting corrosion posts a serious threat to the integrity of pipelines operated in a sour gas environment. A pit may continue to grow thus causing a pipeline to leak, but it may stop growing due to repassivation. To annualize a pitting corrosion rate from the corrosion testing data obtained in a laboratory, one extrapolates the testing duration to a year. Errors are introduced due to the nonlinear pit propagation rate with respect to time. This study is to understand the effect of the testing duration on passivation and repassivation, as well as the calculated pitting corrosion rate. Two corrosion inhibitors were selected to mitigate pitting corrosion. The results in this paper show that H_2S/CO_2 ratio and organic acetic acid content affect the repassivation process, and therefore, influences the pitting corrosion rate. The performance of two corrosion inhibitors shows the effectiveness of inhibiting pit propagation. With the help of the surface profiler using the white light, the authors are able to measure the pit depth to a very high degree of accuracy.