Abstract
Cased pipe segments can suffer external corrosion when the carrier pipe holidays are exposed to electrolyte or humid air. Corrosion by electrolyte occurs when cathodic protection (CP) is shielded by, for instance, insulator spacers, the casing wall (particularly if coated), or mud/deposits accumulated in the annulus. When the casing and carrier are metallically shorted, any CP protection to the carrier pipe may be eliminated. Understanding mechanisms and severity of external corrosion of cased carrier pipe is a significant step toward developing strategies to prevent or mitigate the corrosion problem. The severity of carrier external corrosion can be assessed through a statistical analysis of corrosion anomalies identified and sized from In-Line Inspection (ILI) runs. The results of piggable cased pipe segments can be applied to non-piggable ones given their corrosion conditions are similar. The goal of this study was to investigate the significance of external corrosion damage to cased segments, including the preferential location of the peak anomaly in a cased segment, the effect on corrosion of metallic shorts relative to non-shorted conditions, historical failure incidents in casings, and the relative safety of cased segments to non-cased ones evaluated by the number of scheduled or immediate repair anomalies per mile. These results are expected to provide insight into developing risk methodologies for identification and prioritization of cased pipe segments as part of the external corrosion direct assessment (ECDA) program of cased crossings.
