Pitting and Corrosion Rates of Coated, Uncoated, and Insulated A333 Steel Pipelines in Marine Harsh Environment

Abstract

Abstract Pipelines are one of the most economical and safe means of transporting useful materials, and their design life depends on protection mechanisms present. Marine environments increase corrosion rates due to moisture, and elements like chloride which increase localized pitting rates. Thirty-six A333 low temperature carbon steel pipelines were placed at Argentia, NL, an extremely corrosive environment (C5) near high tide mark. The experiment consisted of coated, uncoated, and insulated pipes. Exposed for a period of two years, corrosion rate, optical inspections, and pit depth were recorded at intervals. The highest average pit and maximum pit depth occurred in uncoated insulated pipes and coated uninsulated pipes. The highest average mass loss occurred in uncoated (insulated and uninsulated) pipes. The least mass loss and pit depths generally occurred in coated pipes (both insulated and uninsulated). Corrosion near the ends of the pipes were more significant than other locations. Final averaged corrosion rates for insulated coated and uncoated pipes, were 0.017 and 0.021mm/yr respectively. Corrosion rates for uninsulated coated and uncoated pipes, were 0.014mm/yr and 0.023mm/yr respectively. Maximum and mean pit depths for insulated coated and uncoated pipes were, 180/156 and 256/205 microns, respectively, while for uninsulated coated and uncoated were 210/177 and 182/148 microns, respectively. Some coated and uncoated insulated pipes had negligible pitting and corrosion. Results provide an increased understanding of corrosion rates, corrosion under insulation corrosion, and under coating, and pitting data for pipelines in service in marine harsh environments.