Time of Wetness in Marine Atmospheres: What Are We Measuring?

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Product Number: 51315-5987-SG

ISBN: 5987 2015 CP

Author: Eric Schindelholz

Publication Date: 2015

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Time of wetness (TOW) a measured estimate of surface wetness duration is a parameter extensively utilized in atmospheric corrosivity models and structural health monitoring applications. Although the basic concept of TOW is generally agreed upon what is meant by “wet” is oftenambiguous and practical determination of this parameter is widely varied. This paper examines the accuracyof current TOW determination methods in the context of marine environments where sea salt aerosol (SSA) is the primary surface contaminant. The hygroscopic behavior of both natural SSA and laboratory proxies are reviewed. Evidence is presented that suggests these chemistries may not fully dry in ambient outdoor conditions. Furthermore the corrosion of mild steel under sea salt simulants is demonstrated to occur down to low humidity levels (< 30%RH) due to the presence of supersaturated brines and adsorbed water on salt crystals. Together these findings bring into question whether TOW is unity in marine environmentsand demonstrate that common wetness sensing methods and estimates using RH thresholds do not fully capture the true TOW of corroding steel surfaces. Avenues for improvement ofdetermination methods and implications for corrosivity models and health monitoring are discussed.