Abstract
The configuration of surface fatigue cracks in 12 inch stainless steel pipes was detected by Direct Current Potential Drop Method (PDM). In the process, a simplified method for determining the surface crack configuration was invented based on the analysis of electrical field by FEM. First, the calibration curves of potential ratio V/V0 vs. normalized crack depth a/t were made for every a/c=0.01 using the relation of potential ratio V/V0 and crack aspect ratio for various crack depths. The crack depth was derived by substituting the maximum potential ratio measured at the crack center into an appropriate calibration curve. The calculated crack aspect ratio was compared with the crack aspect ratio of the calibration curve. If the former differed from the latter, the crack depth was evaluated by the calibration curve with another crack aspect ratio until both of the crack aspect ratio coincided. The whole crack configuration was determined by substituting the potential ratio measured at each position into the coincident calibration curve. The method was applied to the fatigue crack and the crack shape was estimated with the accuracy of ±0.3mm.
