Pitting corrosion models improve integrity management, reliability

The National Polytechnic Institute Mexico City conducted integrity assessment of a coal tar-coated 62-km long underground oil pipeline with a 914-mm OD and an 11-mm WT and reliability analysis of a coal-tar coated, 82-km underground pipeline transporting sweet gas. The institute aimed at demonstrating how pitting corrosion models improve integrity and reliability analyses. Magnetic flux leakage (MFL) in-line inspections (ILI) checked the 62-km pipeline after 18 years of service. Time-to-failure by leakage due to external corrosion pitting facilitated determination of a remaining-life estimate. The first phase of ILI-based integrity analysis employed the linear pit-growth model with the assumption that pits started to crop up when the pipeline was commissioned. The 82-km pipeline OD and nominal WT measured 355.6 mm and 9.52 mm, respectively. MFL-ILI inspection of the pipeline, commissioned in 1981, was done in 2002 and 2007.