Understanding and Mitigating Under-Deposit Corrosion in Large Diameter Crude Oil Pipelines: A Progress Report

This paper is an exploration of factors affecting internal corrosion of transmission pipeline systems (<0.5% S&W), as well as a progress report on research aimed at improving chemical mitigation of this threat in heavy oil product streams. Typical pipeline corrodents and corrodent transport mechanisms are explored. Transmission quality hydrocarbon products are shown to carry micro-emulsified water, various solid particles, solid particles with micro-attached water, and bacteria. While micro-emulsified water can be considered benign owing its ability to be transported harmlessly without accumulation; water-wetted solid particles have sufficient density to reach the pipe floor. Patterns of internal corrosion on a transmission pipeline are used to demonstrate the significance of solids accumulation leading to under-deposit corrosion. Analysis of pipeline sludge reveals significant populations of different bacterial species indicating the existence of a robust biomass capable of creating or sustaining a corrosive environment. Corrosivity testing of pipeline sludges was performed using two static autoclave coupon methods. One test method demonstrated that the addition of chemical inhibitor directly to the pipeline sludge could reduce corrosion rates as effectively as batch treatment of a clean coupon. A rotating mechanical contactor was designed and built to facilitate the blending of corrosion inhibitor with pipeline sludge under ‘like-pipe’ flow conditions, but results of sludge corrosivity testing using this device are not yet available.