A study of magnetic flux-leakage signals

Magnetic flux-leakage (MFL) measurement is the most widely used non-destruc tive technique for in-service inspection of oil and gas pipelines. The effe ct of line-pressure-induced hoop stress on MFL signals has been studied for an electrochemically milled pit (50% penetration) in a 9 mm thick steel pi pe wail. The existing theoretical models for flux-leakage signals are discu ssed. Among them the Zatsepin-Shcherbinin and Edwards-Palmer models have be en fitted to the axial and radial MFL signals. Both the leakage-flux compon ents under various stresses are scaled to make them stress independent.