FACTORS AFFECTING PIPELINE FLAW DETECTION AND MEASUREMENT. ANNUAL REPORT, MAY 1996-APRIL 1997

This report focuses on two techniques for pipeline flaw detection and measurement: Magnetic Flux Leakage (MFL) and Remote Field Eddy Current (RFEC). A number of factors influence MFL signals, the least understood of which are stress and the variation in magnetic properties. In addition to bulk stress, local defect-induced stress concentrations can influence the MFL result significantly. This project therefore continues fundamental research on the effects of line presure stress on MFL signal patterns. Defect-induced stress concentrations have been determined using neutron diffraction and magnetic Barkhausen noise (MBN) measurements, for correlation with MFL results. Finite element calculations have also been carried out to determine the effects of magnetic anisotropy on MFL signals from pits of different shapes. First estimates of stress correction factors for MFL signals have been produced.