Internal corrosion is a leading cause of failure of pipelines that transport crude oil. The small amounts of saline water present in crude oil separates over a period due to any stagnancy or low flow conditions. The separated water causes water wetting of the pipe surface and creates corrosive condition along with the presence of carbon dioxide and hydrogen sulfide and bacteria, especially the sulfate reducing bacteria (SRB) and acid producing general anaerobic bacteria (GAnB) that thrive under the anaerobic conditions existing in pipelines. This is the major reason for pitting and leakages of pipelines.

The On-line Corrosion Monitoring (OCM) using corrosion coupons provide early indication of internal corrosion taking place on the pipe wall. The chemical analysis of deposits removed from cleaning pigging provide qualitative information of general corrosion and its possible mechanism, while the microbiological analysis can indicate the involvement of bacteria in the internal corrosion. In-line Inspection (ILI) conducted on a cleaned pipeline measure pit depth on the internal pipe wall.

This paper analyzes the data collected by each of these internal corrosion monitoring techniques and suggests a means for ranking the internal corrosion severity of crude pipelines of the Oil Field Operating Company, based on interpretation of the data. This ranking can help in optimizing the ILI activities by changing to a need-based program from the current schedule-based program.

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