The Case of Atypical Accelerated External Corrosion inside a Casing

Abstract This paper presents the Root Cause Analysis (RCA) of severe accelerated top side external corrosion of a pipeline within a casing. The pipe was exposed as part of an integrity excavation to investigate fast-growing external corrosion features identified through successive In-Line Inspection (ILI). Upon excavation, the external corrosion morphology was atypical and concentrated along a narrow 1 to 2-inch-wide band at the top of the pipe over the distance of several joints. This paper presents summary information from the ILI along with cathodic protection results, Non-Destructive Examination (NDE) results, and laboratory testing performed as part of a causal investigation. After eliminating the most likely mechanisms of accelerated external corrosion, a rather unusual corrosion scenario was identified. This case study of severe and rapid external corrosion within a casing should be of interest to operators of pipelines where operating temperatures are increasing.