Chapter 35 Use of Large Standoff Magnetometry for Geohazard Pipeline Integrity Investigations

Buried steel pipelines are subjected to mechanical stress emanating from either internal or external forces, resulting from geohazards, shear or external loading, and hoop stress. These conditions are important factors that can be detrimental to the integrity of a pipeline and lead to potential ruptures and failures if not properly and proactively managed with applicable monitoring and / or inspection tools. Some of the failures have resulted from the development of concentrations of stress that have led to dents, ruptures, cracks, buckles, leaks, etc. Pipeline operators have proactively installed ground monitoring devices or frequently performed inspections in the areas that present concern to mitigate problems prior to an incident. These conditions become even more challenging on difficult to pig pipelines driving the need for use of non-intrusive, and non-destructive indirect inspection tools.

Using large standoff magnetometry (LSM), a novel screening technology, has shown strong industry relevance in the identification of stress concentrations for geohazard applications. LSM 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”. This innovative technology can detect changes in the magnetic field of a pipeline which can indicate the presence of stress on the pipe wall. Geometric anomalies (ovalities, dent, wrinkle), hoop stress, ground /slope movement, bend strain, thermal expansion, crack, and material defects are potential sources of stress that LSM can detect from aboveground.

LSM technology has been deployed in several slope monitoring and ground displacement projects to proactively monitor the development of stress concentration zones in areas of concern. The technology is used to perform a baseline inspection in these areas of concern followed by periodic inspections that monitor the change to the magnitude of the stress concentrations that were initially measured with the intent to prevent future failures and limit downtime. In addition, LSM has been used to verify and prioritize stress concentration call-outs by ILI tools in sections that have developed dents, buckles, crack, SCC, leaks, etc., due to environmental conditions.

This paper summarizes the use of LSM in several pipeline integrity geohazard assessments, that were conducted on different oil and gas pipelines, to identify dents, crack, buckle, slope movement, and other geotechnical anomalies. Lessons learnt from practical real-life projects and validations of the technology are presented to demonstrate the effectiveness of LSM for geohazard applications.