THE EFFECTS OF DEFECT DEPTH AND BONDING STRESS ON MAGNETIC BARKHAUSENNOISE AND FLUX-LEAKAGE SIGNALS

Magnetic-flux-leakage (MFL) measurements are used for corrosion inspec tion of buried oil and gas pipelines. MFL signals are sensitive to the depth of defects, such as corrosion pits, in the pipe wall and to ext ernal stresses generated mainly by the line pressure. MFL signal varia tions have been studied from the inside wall in the presence of variou s circumferential bending stresses and magnetic flux densities for thr ee outside wall pits of depths 30%, 50% and 80% of the wall thickness. Magnetic Barkhausen noise (MBN) measurements have been used to study the stress-induced changes in the direction of the bulk magnetic easy axis and directional anisotropies of the pipe wall, These help one to understand the stress-dependent MFL results.