Condensation of supersaturated water vapor in mineral wool subjected to a temperature gradient: An NMR study

Insulated pipelines located outdoors are subjected to fluctuations in ambient temperature and humidity. Weather conditions significantly contribute to humidity migrating into pipe insulation, and subsequent condensation on the cold side within the system. Corrosion under insulation (CUI) is a degradation mechanism closely related to prolonged impact of retained liquid water on the pipe metal surface beneath the insulation. However, the thermodynamic parameters that indicate condensation within mineral wool insulation remain insufficiently investigated. In this study, we present experimental work using nuclear magnetic resonance (NMR) to measure moisture content in mineral wool subjected to a temperature gradient and air with controlled relative humidity at the warm side. The results show that significant supersaturation of humid air occurs before and during condensation, and that the condensation region length increases linearly with the relative humidity of the warm air. The measured moisture content is close to the values estimated with a simple mass conservation model. These findings have important implications for monitoring temperature and relative humidity in mineral wool insulation to asses the amount of condensed liquid water in a thermal gradient, thereby improving methods for detecting corrosion under insulation.