Abstract
Hydrogen Induced Cracking (HIC) is a major issue of line pipe steels exposed to sour environments. Enormous efforts in research and production have been done by steel makers to improve HIC resistance. It is widely recognized that adding copper is effective to decrease HIC susceptibility in mildly sour environments with high solution pH (normally more than 5.0). However, the mechanism to describe the effect of Cu on the HIC suppression has not been fully clarified. In this study, hydrogen permeation testing was conducted in sour conditions using Devanathan type cell and the effect of Cu on HIC resistance was investigated under two different sour conditions (0.1MPa H2S and 0.001MPa H2S). Corrosion product formed on surface was also investigated to characterize its structure and element distribution when it has protective performance against hydrogen entry. From those electrochemical measurements and analysis techniques, it was found that Cu tended to be enriched near the steel in the corrosion product and that suppress hydrogen entry in mildly sour conditions at 0.1MPa H2S. However, remarkable effect of Cu was not observed under low H2S partial pressure. The mechanism of HIC suppression by Cu addition will be discussed in this paper.
