In our experimental laboratory system the MFL magnet is stationary and (for this study) could be configured to produce a range of pipe wall flux densities up to 1.8T. The two flux densities examined were 1.4T and 1.8T – these correspond to the flux densities produced in pipe walls by moderate and high flux density inspection tools. The sensor uses a Hall probe as a sensing element, attached to the arm of an XY plotter, allowing a 40mmx40mm area to be scanned above a defect region at 1mm intervals. It can be oriented to measure either the axial, radial or circumferential components of the leakage flux signal, and is connected though an amplifier to a
PC-based data acquisition system. In this paper, only the radial MFL signal will be considered. As an example,
Figure 2 shows a typical surface and contour plot of the radial MFL signal from a 14mm diameter, 50% penetration pit in a pipeline section.