Effects of bending stresses on magnetic flux leakage patterns

Abstract

Abstract The effects of stress on magnetic flux leakage patterns induced by pits in pipeline samples are examined using separate arrangements to produce surface or through wall bending stress. The test samples are long strips cut axially from a sample of pipeline. The first sample is a single strip bent as a beam to induce surface stresses. The second is a composite beam with two steel strips separated by a bonded glass-fibre and wood layer bent to give nearly uniform but opposite stress induced in each steel strip. Maps of the radial magnetic flux leakage amplitudes from identical defects in the two beams were compared for response to bending stress. The results show that surface stress alone is insufficient for considering the effects of stress on magnetic flux leakage amplitudes. The uniformly stressed composite beam showed considerably higher response to stress than the single strip sample with bending producing predominantly surface stress.