Combining hygrothermal and corrosion models to predict corrosion of metal fasteners embedded in wood

A combined heat, moisture, and corrosion model is presented and used to simulate the corrosion of metal fasteners embedded in solid wood exposed to the exterior environment. First, the moisture content and temperature at the wood/fastener interface is determined at each time step. Then, the amount of corrosion is determined spatially using an empirical corrosion rate model and the inputs of the first step. The result is a corrosion profile along the length of the fastener generated by summing the corrosion depths determined at each time step. We apply the combined model to predict the annual corrosion depth along a metal fastener in wood decks situated in nine different US cities. Corrosion profiles are found to exhibit the same general shape independently of climatic load, with the largest amount of corrosion occurring at 1–5 mm from the wood surface with corrosion depths ranging from 5 μm in Phoenix, Arizona to 45 μm in Hilo, Hawaii. Corrosion is confined to the first 7–20 mm of the fastener below the wood surface. By varying the climatic loads, we find that although there is a definite relation between total annual rain and total annual corrosion, under the same rain loads corrosion is higher for a climate with more evenly distributed rain events. The proposed combined model is able to capture corrosion behavior under varying loading. A sensitivity analysis gives guidelines for future corrosion modeling work for fasteners in wood.

► A model is presented for the corrosion of metals embedded in wood exposed outdoors.
► One year simulations were run for 9 different US cities.
► The most corrosion was modeled in Hilo, Hawaii; the least in Phoenix Arizona.