Detection of Configuration of Surface Cracks at Inside Surface of a Pipe from Outside Surface by DC Potential Drop Method

The configuration of surface cracks has been detected by Direct Current Potential Drop Method (PDM). A simplified method for determining the reverse-face crack configuration was invented based on the FEM analysis of electrical fields near the surface cracks with different aspect ratios and depth. Here, the reverse-face crack is defined as the crack existing on the opposite side of the detecting surface of structural material, while the crack detected on the same side is defined as the surface crack. The newly developed method was applied to the detection of the fatigue cracks on the inside surface of 2 inch stainless steel pipes subjected to tensile cyclic stress. The potential difference distribution near the surface cracks was measured by using many potential difference measuring electrodes placed along the reverse-face cracks on the outside surface of the pipes with the same spacing as the wall thickness. The potential difference distribution obtained by the present simplified method showed that the reverse-face crack configuration could be determined with relatively good accuracy, if the crack depths were more than 30% of the wall thickness. Thus, the potential drop method is considered to be appropriate for an on-line monitoring system of the reverse-face cracks.