Severe corrosion and operating problems due to deposition of solids in an offshore gas re-injection system were investigated. Potential corrosion mechanisms were identified and matched to the morphology and location of the observed corrosion damage. Predicted corrosion rates were compared with observed corrosion rates. Carbon dioxide, hydrogen sulphide, oxygen, elemental sulfur, chlorides methanol and combinations thereof were considered. Corrosion due to elemental sulphur was identified as the mostly likely cause of corrosion. The sulphur drop was the result of reaction between hydrogen sulphide and oxygen following oxygen ingress into the sour process gas. Further corrosion was prevented by eliminating the source of oxygen ingress. This also solved the operational problems created by the solids.
Keywords: CO2, H2S, oxygen, sulfur, methanol, chlorides, subsea, corrosion