L52270 Basics of Metal Fatigue in Natural Gas Pipeline Systems - A Primer for Gas Pipeline Operators

The natural gas pipeline industry is rapidly implementing comprehensive integrity management practices to meet the demands of new regulatory imperatives and public interests. These new demands require formal integrity management planning programs be developed and applied where pipeline failures could affect High Consequence Areas. A formal integrity management plan (IMP) incorporates some process for identifying threats to a pipeline's integrity. Such threats come in many forms and are uniquely dependent on a wide range of attributes associated with an individual pipeline segment. Interest (or concern) has arisen regarding metal fatigue as one such possible integrity threat. We know from some pipeline failures that occasionally and under certain circumstances, fatigue may constitute a potential threat.

The cumulative body of knowledge derived by theory, test, and experience on the subject of fatigue and its effects on piping, pressurized equipment, and welded structures is vast in scope and detail, and it is not the intention of this document to summarize that. Rather, it is intended that this document provide natural gas pipeline operators and others interested in natural gas pipeline safety with a useful understanding of the extent to which fatigue could pose a legitimate and actionable safety threat, as well as to demonstrate the author's opinion that in most respects, fatigue remains a comparatively minor risk component of the overall spectrum of threats to natural gas pipeline safety.