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 H2S/CO2 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.
Key words: sour corrosion, pitting corrosion, pit propagation, organic acid