A Discrimination Method of Three Types of Defects in Insulated Cladding Components Based on the Lift-off Effect of Capacitive Imaging (CI) Technology

In insulated cladding components, simultaneously detecting and distinguishing surface defects on the insulation layer, hidden defects in the insulation layer, and surface defects on the metal layer of insulated cladding components can help in formulating appropriate maintenance plans and promptly eliminating safety hazards, which is of great significance for ensuring the safety of insulated cladding components in relevant application fields. This paper applies capacitive imaging (CI) to detect three different types of defects. A three-dimensional simulation model of the CI sensor detecting the three types of defects is established using COMSOL software. The corresponding measurement sensitivity distribution (MSD) and volume of influence (VOI) are obtained, and the detection mechanisms of the three different types of defects are analyzed in detail. By analyzing the lift-off height variation, the VOI regions' changing patterns for different types of defects are determined, and the distinguishing mechanisms for the three types of defects are obtained. Based on the monotonicity of the normalized variation ratio (NVR) and the differences in the positions of the intersection points, a comparative distinguishing method for the three types of defects based on the variation of the lift-off height is established. Experimental results demonstrate that the defect comparative distinguishing method based on the lift-off effect can effectively differentiate surface defects on the insulation layer, hidden defects in the insulation layer, and surface defects on the metal layer.