MFL is capable of detecting the presence and location of significant longitudinally or transversely orientated defects such as pits, scabs, slivers, gouges, roll-ins, laps, seams, cracks, holes and improper welds in ferromagnetic tubes under inspection. In addition, the severity of electromagnetic indication produced by the discontinuity may be estimated and a rejection level set with respect to the magnitude of the electromagnetic indication produced by the discontinuity. Thickness measurement of piping and storage tank pressure vessels.