Identifying Stress Concentrations on Buried Steel Pipelines Using Large Standoff Magnetometry Technology

Abstract

Buried steel pipelines are subjected to mechanical stress, by internal or external forces, resulting from geo-hazards, shear or external loading, and hoop stress. These conditions are key factors that can be detrimental to the integrity of the pipeline and lead to possible failures such as: coating damage, dents, buckles, cracks, and leaks. Identifying stress concentration regions, in difficult to pig pipelines, is challenging, especially when compared to piggable pipelines. Using the Large Standoff Magnetometry (LSM) technology, an innovative screening tool, we can identify stress concentration by performing an indirect inspection. LSM technology detects inverse magnetostriction (also known as the Villari effect) “which is the change of the magnetic susceptibility of a material when subjected to mechanical stress”. Using this technology we can detect changes in the magnetic field of the pipeline which can indicate the presence of stress on the pipe wall. LSM technology has shown significant results when correlated with additional data. For instance, LSM technology correlated with Inline Inspection (ILI) or As-Built drawings have aided in the accurate selection of digs to mitigate failures due to stress concentration. Successfully identifying digs to mitigate stress concentration is vital as it substantially reduces cost due to potential failures and avoiding unnecessary digs. This paper will show the benefits of an integrated approach and how the correlation of inline and aboveground pipeline integrity data ensures that threats due to stress concentrations are confidently identified and mitigated. Several case studies will be presented to show how recent advancements have helped to identify and prioritize regions with Stress Corrosion Cracking (SCC), Cracks, Unknown Buried Feature, Dents, and Buckles.