Accurate measurement of pipe wall reduction: High-precision instrument and minimization of uncertainties

The magnetic flux density method is suited for monitoring the pipe's wall thinning. However, the quantification of gradual reduction is challenging because its small signal is hindered inside the noise floor of magnetic field measurements. In this work, a high-precision instrument for the accurate measurements of small thickness reductions is presented. The size of a magnetizer is optimized with respect to the size range of pipes and minimization of the wobble effect. The flux density is measured by our ultrahigh-sensitivity magnetometer with a resolution of 1.4 nT and dynamic range from 0 to 50 mT. For reliable measurements, we investigate the appropriate strengths of the magnetizing field, appropriate sensor lift-off distances, and minimizing contributions from other uncertainties, such as signals at the pipe's ends and magnetic flux leakages from abrupt defects. Finally, a real-time measurement of the 12.5 % standard wall reduction sample is found to be highly reliable and reproducible.