Sweet Gas Corrosion, or CO2 corrosion, is one of the main corrosion mechanisms in oil and gas industry. It results from presence of water containing dissolved carbon dioxide CO2. This phenomenon is influenced by the partial pressure of carbon dioxide, temperature, flow regime and water content.
Over the past few years, concern has grown for sweet gas corrosion in some Saudi Aramco Gas gathering facilities. Severe localized corrosion was noticed in some gas wells piping.
The metallurgy used for surface gas piping is seamless carbon steel in production line spools, flow lines and trunk lines. Corrosion resistant alloy (CRA) is used for the valves to prevent corrosion in the body cavity.
Investigation studies and piping UT surveys were conducted at different areas to assess the severity and extent of such phenomena. Turbulent flow was found to be the major factor for severe sweet gas corrosion in first two spools downstream of wellhead wing valve as well as in spools upstream & downstream of choke valve. Furthermore, insufficient dosage rate of corrosion inhibitor contributed to high metal loss in downstream section of the choke valve in some wells.