Definition - What does Capillary Condensation mean?
Capillary condensation refers to a process where vapors are adsorbed into porous avenues of a metal via multi-layer mechanisms, which results in a condensed liquid accumulating in these pockets. Moisture accumulation is responsible for a higher corrosion rate.
Corrosionpedia explains Capillary Condensation
Capillary condensation occurs when vapor condensation is below the saturation vapor pressure of the pure liquid fraction of the same substance. This is described by an increase in van der Waals interactions between vapor phase molecules inside a confined space (a capillary, pocket or vapor space). Once condensation occurs, a liquid-vapor interface analysis may be performed to determine the equilibrium point below the saturation vapor pressure.
Therefore, condensation and corrosion can occur in narrow capillaries at pressures that are lower than the normal saturation vapor pressure.