Large standoff magnetometry (LSM) as a non-intrusive NDE technology has been used many years in commercial trials for above-ground detection of underground pipeline anomalies associated with stress concentration zones (SCZs). As a passive geo-magnetization flux leakage measurement method, it has been mainly targeting common anomalies such as corrosion, gouges/dents and cracks that are often very localized in small scale. Insufficient consistency and reliability are still the major concern due to technical challenges in getting high resolutions and signal strength at large standoff distance. In comparison, geohazard related external forces induce much large-scale elevated stresses/strains with stronger stress-magnetization signals. Lack of economically viable solutions for pipeline screening and monitoring under geohazard conditions provides a good opportunity to establish LSM’s market position.
This work is part of Pacific Gas and Electric Company’s effort in better fundamental understanding of the state-of-the-art LSM technology and its potential to enhance the current industrial practices of pipeline assessment under geohazard conditions. Specifically, 3D mapping of pipelines including depth of cover (DOC) measurement, locating girth welds and peak stresses/strains with risk rating, verification of strain relief operation and continuous monitoring afterwards. Inline inspection (ILI) and geotechnical analysis data together with field excavation and strain-gauge data are utilized as references to cross-check the LSM results. The outcomes indicate geohazard application is very likely a viable application for LSM technology in near future.