Corrosion Processes of Steel-Hulled Potentially Polluting Wrecks

Abstract

AbstractSubmerged metals are continuously affected by the chemical processes of corrosion, the destructive degradation of metal by chemical or electrochemical reactions within the marine environment (Valenca et al., 2022:2–3; Venugopal, 1994:35). Over time, metal ions at anodic sites defuse into electrolytic solutions from the oxidising reactions occurring at cathodic sites, causing the creation of corrosion byproducts, like rust on iron, and the loss of structural mass. The different reduction reactions in the microstructures of alloys and the imperfections found within refined materials, like carbon slag in steel, are targeted by this process, essentially reverting the chemically unstable materials back to their more stable original forms (Moore III, 2015:192; MacLeod 2016:90–92). The deterioration of metallic shipwreck hulls has become a growing concern within the field of marine conservation as many of the fuel tankers deliberately targeted in WWII threaten to release trapped fuel and chemical cargoes after nearly eight decades of exposure to a range of corrosive environments (Barrett, 2011:4–5). With the deterioration rate of ship hulls averaging at around ±0.1–0.4 mm of loss per year and the thickness of ship deck plates from the 1940s to the 1960s ranging generally from 1–4 cm in thickness, the window to act on the majority of potentially polluting shipwrecks (PPW) before a catastrophic breach occurs is closing (MacLeod, 2016a:8; Beldowski, 2018:249; Masetti, 2012:33; Masetti & Calder, 2014:139).