Assessment of a Corrosion Under Insulation (CUI) Using DNV RP-F101 Procedure

Corrosion under insulation is a typical type of localised corrosion in oil and gas industry especially when water penetrates into a damaged thermal insulation/coating. An area of corrosion under insulation (CUI) was observed on the external surface of a pipe on topside of an offshore platform after removing the insulation. Surveys of depth measurements of the corroded area in both longitudinal and circumferential directions (with respect to the pipe axial direction) using a depth micrometer tool were performed and then converted to a river-bottom profile following the procedure of DNV RP-F101 Part A. A best estimate of the failure pressure safe working pressure (maximum operating pressure) of the pipe were calculated. The former was then compared against the finite element analysis (FEA) results which showed good agreement when axial stresses were excluded. The effect of assumptions such as confidence level and inspection sizing accuracy are also discussed.