Evidence of hydrogen gas evolution accelerating the cathodic coating delamination

Abstract

For coated pipelines with cathodic protection, cathodic delamination has been recognized as one of the main causes of coating degradation. A thorough understanding of the cathodic delamination mechanism would benefit to pipeline integrity. The mechanism of local alkalization has been taken root in recent years, while the contribution of hydrogen gas evolution is still controversial. In this work, the mixed-potential theory was introduced to calculate the test time ratio of cathodic delamination, with or without hydrogen gas. The wire-beam electrode was also used to monitor the local electrochemical information. The results show that the hydrogen gas remarkably promotes the delamination process. For 100 μm single layer epoxy coating, when the applied cathodic potential was −1.5 V (vs. SCE), the contribution of hydrogen gas is around 38.7%. The findings will help build a full understanding of cathodic delamination and provide new insight into its mitigation.