Verification of Internal Corrosion Through ILI and Non-Destructive Testing: Lessons Learned

Abstract Verification of In line Inspection results is often challenging for pipelines with internal corrosion, especially in areas of extensive corrosion and/or areas with challenging corrosion morphologies such as pinhole corrosion (as defined by the Pipeline Operators Forum [1]). The most reliable method which many operators choose is to rely on cut-outs for the purpose of both mitigation and ILI verification. However, depending on the diameter and the criticality of the pipeline, verification of internal corrosion features from in line inspection may be based exclusively on ultrasonic (UT) non-destructive examination (NDE). These ultrasonic inspection techniques can range from hand-held pencil probes to automated scanning systems. The output from these methods does vary both in quantity and quality which can and does impact the potential tool validation as per API 1163 [2]. This paper outlines the results from these different inspection techniques and then compares it to laser scan and pit gauge measurements once the inner surface of the pipe wall is available. This work was done across multiple pipeline diameters and various internal corrosion mechanisms. It reviews the strengths and weakness of the individual NDE measurements and compares them to the original Magnetic Flux Leakage (MFL) inspections from the perspective of validating the inline inspection. An output from this study is a series of guidelines that should be used when verifying internal corrosion that both operators and tool providers can use to determine tool performance. These guidelines help to verify both the ILI tool performance as well as the relevant non-destructive method.