Improving the Accuracy of Onshore Pipeline Remaining Life Assessments and Optimising Field Verification Activities from Detailed Assessment of Corrosion Metal loss Feature Interactions

Abstract

This paper discusses approaches to improve the accuracy of onshore pipeline remaining life assessments and optimise the targeting of locations for field verification activities via detailed assessment of reported corrosion metal losses and corrosion feature interactions. The overall aim is to show how confidence in assessments can be increased while ensuring adherence to industry standards. Evaluation of interactions between corrosion features is a necessary consideration as specified in industry standard fitness-for-service (FFS) methodologies. In accordance with developed FFS standards, if corrosion features are sufficiently close together, they should be considered to act as a single, larger feature. However, in the authors' experience, detailed assessment of corrosion feature interactions is not always performed. This can lead to overly optimistic/pessimistic results, and a subsequent lack of focus for future field verification activities with respect to inspection locations and techniques. FFS assessments are often based on results from in-line inspections (ILIs), which, depending on the pipeline condition, can report many thousands of individual corrosion features. In the case of heavily corroded pipelines, where corrosion damage is reported along approximately the same orientation (for example at 06:00, the bottom of the line), inadequate consideration of corrosion feature interactions could significantly overestimate the maximum allowable safe pressure of the pipeline. In contrast, conservatively assuming a grooving metal loss morphology and simplifying FFS calculations to assume infinitely long corrosion can appreciably lower calculated safe pressures, resulting in premature remediation activities (such as repairs, de-rating). In both cases, neither method of assessment allows specific targeting of field verification activities as areas of maximum corrosion interaction will not have been determined. This paper will demonstrate the benefits of performing a detailed assessment of corrosion feature interactions during an integrity assessment in comparison to overly optimistic or simplified assumptions, and show the benefits of such detailed assessment with respect to future field verification activities.