Improving the detectability and confirmation of hidden surface corrosion on metal sheets using active infrared thermography

Abstract

This research aims to provide a simple approach to detecting and determining hidden corrosion using active infrared thermography with improved consistency in distinguishing hidden defect areas of metal sheets (galvanized steel and stainless steel) commonly used as part of building envelopes. Early studies on detecting hidden defects focused primarily on defects resulting from material loss. Equally important is the early detection of corroded metal surfaces hidden from the observer's plane of view through non-invasive means. In this study, two heating configurations using portable heaters were explored, along with two analysis approaches to aid in detecting and confirming the presence of hidden corroded surfaces. Metal sheets with or without hidden surface corrosion are detected, distinguished, and confirmed by observing differences in their mean surface temperatures and temperature distribution. The detection and confirmation involve two simple analysis approaches: (1) observing the differences in mean surface temperature and visual thermal contrast of the non-corroded surface available for monitoring during the heating-cooling cycle; and (2) comparing the distribution of temperature probability at a given temperature. The new method is considerably more practical as it would require only heating the region of interest to a temperature of no more than 70 °C using a portable heat source and detailed analysis requiring temperature distribution between 40 and 70 °C. The results from the detection and confirmation approaches also conform with basic principles of heat transfer, making the detection and analysis method not only practical but also scientifically sound. This method may potentially be adopted in building surveys, early detection, and post-monitoring of hidden corroded surfaces that may impact building envelope deterioration and structural integrity.