Stray current corrosion is an external damage mechanism that might pose a threat to integrity of buried pipelines. This type of external damage mechanism typically occurs when a current from nearby cathodic anode bed takes an unintended path and either initiates or accelerates existing external corrosion processes. The objective of this paper is to present a case study wherein severe external metal loss occurred on a major crude pipeline in a relatively short time due to stray current corrosion. The paper will also discuss the robust integrity management plan that allowed the external corrosion to be identified in a timely manner, the active steps taken to restore the integrity of the pipeline, and actions implemented to mitigate further external corrosion from occurring.
The company operates several thousands of kilometers of pipelines that transport oil and gas from the offshore and onshore fields. A Risk Based Inspection (RBI) approach is adopted to ensure the safe operation of the pipeline system in accordance with the design, company, and legal requirements.
During one of the many planned In-Line Inspection (ILI) programs undertaken to determine the integrity status of their pipelines, a 48" crude pipeline was reported to have significant external corrosion on one of its onshore sections with reported metal loss of up to 93% of its nominal wall thickness. Verification digs were conducted and confirmed that the pipeline was riddled with areas of severe external corrosion.
The purpose of this paper is to present a case study regarding the extent of external corrosion that can occur as a consequence of degraded external corrosion protection measures on a buried onshore pipeline.
The 48" crude pipeline carries crude from an offshore field to the onshore plant. The pipeline was constructed in 1976 and has not had significant integrity issues until now. Most of the pipeline is located subsea except for the last 3 kilometers, which are located on the onshore section; please refer to the table below for details.
