Effects of Stress on Flux Leakage

Many theoretical, design, and operational issues affect the accuracy of MFL tools. Mechanical stress is one such variable because it affects the magnetic properties of the pipe steel.

To reduce the effect of stress, the latest generation of MFL inspection tools uses extremely high magnetic intensities to detect and size metal-loss defects. High magnetization intensities reduce the effects of inherent material property variations, residual stresses, and many other inspection variables. At lower magnetization levels, these magnetic property variations are thought to impede the detection of small metal-loss defects and characterization of the defect size.

Stress-induced changes in signal, often considered noise since they alter the flux leakage response from metal-loss defects, may contain additional information about the cause of the defect and the state of the defect that could be used to assess integrity. Stress-induced changes in signal could also be used to detect other defects in the pipeline.