The objective of this paper is to share experience gathered from the ongoing integrity management of brownfield production flowlines, to help support future improvements in Fitness-For-Service (FFS) and Life Extension (LE) assessment methodologies, specifically for the case of corrosion features located in regions of higher fatigue loading.

The paper describes the nature of the problem being considered. This is followed by a brief review of the current state of flowline inspection technology to provide additional context. Industry standard practice and complementary literature relating to the assessment of corrosion features subject to fatigue loading are then reviewed. A possible enhancement to existing FFS methods for such cases is described. A hypothetical example is used to compare the different FFS assessment methods, including the "enhanced method." The findings are then reviewed and discussed addressing the limits of applicability and the advantages and disadvantages of each method, and conclusions are drawn.

Today's inspection equipment can provide information about the condition of a flowline, which is of great value for FFS and LE assessments. However, it will likely be some time before there are inspection tools available that can reliably detect and accurately size cracks growing from within corrosion features. This is particularly challenging when considering inspection over an extended length of flowline and within a practical timeframe. Therefore it is important to have a robust, rational and standardized method for assessing the fatigue life of detected or suspected corrosion features in the absence of specific knowledge about existing fatigue cracks within those features. Industry standards are somewhat limited in addressing this scenario with two quite different methods suggested.

The hypothetical example presented in this paper shows how those two methods might lead to inappropriate decisions regarding fitness-for-service, depending on specific circumstances. An initial investigation of an incremental enhancement in the methodology suggests that meaningful improvement is possible, and that further work in the area could be of significant value to the industry, helping to ensure appropriate run-repair-replace decision-making in the future.

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