The Effects of Angular Displacement on Magnetic Flux Leakage Metal Loss Signals

Magnetic flux leakage  ILI (In Line Inspection) is used by pipeline operators worldwide to detect and characterize a broad range of pipeline features and anomalies.  Magnetic flux leakage data signals are influenced by the shape and configuration of metal loss zones; with the feature shapes used as a basis for algorithm development and interpretation techniques developed to provide estimates of metal loss lengths, widths and depths.   For pipelines, primary lengths and widths of features may be oriented in any random direction with respect to the pipeline axis and applied magnetic fields.  In addition to field levels, material properties, velocity effects, length, width, and depth, feature orientation will also influence the magnetic field data acquired for typical pipeline metal loss anomalies.  Difficulties encountered in characterizing specific classes of metal loss features have led to the development, implementation, and use of tools employing multiple axis sensors in an effort to improve performance for these categories of metal loss features.   To demonstrate the effects of feature orientation, examples will be presented with the results providing insights into the signal response for metal loss zones as the angular orientation of the features are varied within the applied magnetic field.