Chloride Induced Stress Corossion

Oil and gas industrial assets process hydrocarbons, which include several light and heavier components. The hydro-cracking process involves the cracking of gas oil to produce diesel and other marketable products. The containment leakage in an oil refinery can not only lead to unit shutdown but also have a significant impact on the safety of the operators involved. According to the author’s previous experience, poor operating and maintenance practices often result in pressure vessel and piping failures

This article describes the stress corrosion cracking of a patch repaired elbow in hydrocarbon service, and provides some lessons on corrosion management under the theme of asset integrity. A brief discussion on asset management to avoid SCC crack repair is also given. One pipe elbow in hydrocarbon service prematurely failed during normal operation. This failed elbow was patch welded to arrest the crack and put back into service. However, after being in hydrocarbon service for less than a month, it started leaking again, and a minor fire was reported. The ruptured pipe elbow was taken out of the piping loop (Figure 1), and a sample was taken from this for assessment. This elbow had failed earlier due to chloride stress corrosion cracking. The SCC cracks were further propagated beyond the patch region (as shown in Figure 1) and resulted in leakage. This case study deals with the fact that the repair of the failed pipe was improperly implemented and brings an awareness about use of approved repair procedures and ongoing corrosion management to mitigate SCC failure, and risk assessment.

Conclusion

The patch welded elbow on hydrocarbon service was analysed to determine the root cause of leakage. It was confirmed that prior to patch weld, the elbow suffered from chloride SCC. After patch welding and repair, the leakage could not be arrested due to poor corrosion management. Moreover, an improper repair procedure was employed without identifying the failure cause, which aggravated the corrosion issue resulting in faster crack propagation in actual operating condition. This study provides a valid basis for not to attempt any repair in operating equipment without detailed investigation and tested solution.

Subramanian, C. (2023). Chloride Induced Stress Corrosion Cracking. A journal of the Institute of Corrosion Management. Issue 174 July/August 2023. Retrieved from https://www.icorr.org