Wetting phenomena and time of wetness in atmospheric corrosion: a review

The concept of time of wetness (TOW) is extensively used in the atmospheric corrosion disciplines for such purposes as corrosion prognostics and environmental corrosivity classification. Time of wetness can generally be defined as the amount of time a metal surface remains wet during atmospheric exposure. Although the basic concept and importance of TOW in governing atmospheric corrosion is generally agreed upon, what is meant by “wet” has generally remained ambiguous and its practical determination has been widely varied throughout its history. The objective of this review is to demystify TOW in terms of definition and measurement and identify issues that inhibit this parameter from providing deeper insight into the effect wetness duration has on atmospheric corrosion. Specifically, this paper summarizes the current state of TOW determination methods along with the parallel concept leaf wetness used in environmental science. Furthermore, wetting and drying phenomena associated with atmospheric corrosion and thought to control TOW are overviewed. From this framework, current issues and limitations of TOW are identified and avenues for further improvement suggested.