Understanding the extent of detectability and heat transfer characteristics of hidden defects on metal-based envelopes

Abstract

Metal hidden defects can either be due to corrosion or voids. The extent of their detectability and heat transfer characteristics, particularly with light-colored surface paints and assembly configurations, have been less explored. Observing surface thermal contrast and rate of temperature change (RTC) during “long-pulse” excitation can detect hidden defects regardless of the metal type, paint color, and assembly configuration. However, results from the active thermography approach only indicate their presence and not their location and type. Corroded layers have a lower surface temperature and RTC due to faster heat transfer, while pitted layers have a higher surface temperature and RTC.