Experimental Study on the Influence of Galvanized Iron Sheet Protective Layer on Pulsed Eddy Current Testing

Petrochemical equipment is often insulated by a cladding layer consisting of a metal cladding and an insulation. The application of pulsed eddy current testing (PECT) technology enables the detection of corrosion in the equipment wall thickness without removing the cladding layer. However, when the metal cladding is galvanized iron, it can interfere with the pulsed electromagnetic signals, increasing the error in the detection results and reducing the stability of the detection. In this study, a PEC testing platform was constructed to analyze the impact of variations in the thickness of the galvanized iron and the insulation on the pulse detection. The results indicate that the shielding effect due to the high-magnetic permeability characteristic of the galvanized iron and the induced eddy currents can affect the attenuation of the detection signal and the characteristic curve. As the thickness of the galvanized iron increases, the difference in the late-stage attenuation of the detection signal for samples of different thicknesses becomes smaller. When the thickness of the insulation is increased to 50 mm, the detection signals essentially coincide, making it impossible to calculate the thickness of the tested piece through the characteristic curve. This research provides a reference for the analysis of influencing factors in the PEC testing process and offers technical support for the safe and healthy evaluation of equipment with insulation.