Corrosion Characterisation under Coating Using Pulsed Eddy Current Thermography

摘要

Pulsed eddy current (PEC) thermography is proposed as a powerful Non-destructive Evaluation (NDE) technique, allowing the operator to observe the heating developed from the eddy current distribution in a structure using infrared imaging, detecting defects over a relatively wide area within a short time. In this paper, the use of PEC thermography is investigated to detect corrosion on steel structures. The response of corrosion under a coating is a complex mix of many factors including electrical conductivity, permeability, thermal conductivity, heat capacity, density and surface morphology of rust and coating material, which all have to be taken into account in the analysis of the PEC thermography response. Firstly, the analytical model is developed according to the coupling of electromagnetics and heat conduction. Then, the FEM model of coated corrosion on steel plate is developed and studied in COMSOL Multiphysics. Next, uncoated and coated mild steel (S275) samples with naturally produced corrosion, provided by International Paint, are tested. Based on the modelling and experimental studies, the surface thermal profile and two related features are presented to characterise corrosion with exposure times between 1 to 10 months and different surface preparation. The work shows that PEC thermography can be used for detection and characterisation of coated and uncoated corrosion in industry.