PR-337-063508-R01 Dual Field Magnetic Flux Leakage (MFL) Inspection Technology to Detect Mechanical Damage

This report details the development and testing of a dual magnetization in-line inspection (ILI) tool for detecting mechanical damage in operating pipelines, including the first field trials of a fully operational dual-field magnetic flux leakage (MFL) ILI tool. Augmenting routine MFL corrosion inspection of pipelines using high magnetic fields, this in-line inspection technique detects and assesses mechanical damage using a second lower magnetic field. Nearly all commercially available MFL tools use high magnetic fields to detect and size metal loss such as corrosion. A lower field than commonly applied for detecting metal loss is appropriate for detecting mechanical damage, such as the metallurgical changes caused by impacts from excavation equipment. The lower field is needed to counter the saturation effect of the high magnetic field, which masks and diminishes important components of the signal associated with mechanical damage. At low fields, other properties such as pipeline chemical composition, grain structure, and fabrication methods can also be detected.