Evaluation of shims, gaussmeter, penetrameter, and equations for magnetic particle inspection

Quantitative quality indicators (QQIs) for magnetic particle inspection have previously been reported on by the authors. However, this present evaluation was performed to show the quantitative nature of these shims when placed on identical parts having variable permeability. The evaluations included placing the shims on parts with natural discontinuties and then recording the amperage and magnetic flux density required to reveal the 30 percent depth of discontinuity in the shims. A comparison was also made between the indications produced by shims and Magnetotest penetrameter when the anomalous parts were inspected in accordance with specification requirements of 0.003 to 0.006 T (30 to 60 G). The results of this evaluation show that good indications are obtained on the shims and penetrameter at 0.003 to 0.006 T (30 to 60 G). The evaluation also revealed that the equation for longitudinal magnetization in a coil overmagnetizes the parts and produces a heavy background of oxide on the surface of the parts. It was also determined that there was no difference in results between parts which were heat treated or annealed. Lastly, if was determined that the upper limit of 31.5 A/mm (800 A/in.) required by existing standards for circular magnetization also causes overmagnetization and gaussmeter readings in excess of 0.006 T (60 G). Hence, the requirements in existing standards need to be corrected.