Long-term under-deposit pitting corrosion of carbon steel pipes

Some steel water injection pipelines used to increase the yield from oil production reservoirs in the offshore oil industry have experienced severe channelling corrosion at the 6 o′clock position. The examination of field observations suggests both under-deposit corrosion (UDC) and microbiologically influenced corrosion (MIC) are likely to be associated with the phenomenon. Long-term laboratory experiments are described to distinguish the relative contributions of the presence of deposits, MIC and nitrate addition to the formation of channelling corrosion. Half-pipe steel specimens were exposed to different simulated test environments up to 365 days. The analysis of pitting morphology and pitting depth shows the synergistic effect of MIC and under-deposit corrosion led to severe localized corrosion. Nitrate addition caused most severe localized corrosion. Extreme value distribution examination shows Gumbel function is not appropriate to describe all the pit depth data for 1 year exposure. The results have implications for the corrosion management in industrial practice.