Study of Various Corrosion Protection Coatings for Threaded Fasteners under Insulation

Abstract Corrosion under insulation (CUI) is a significant issue arising from the entrapment of moisture on metal surfaces covered with insulation. The fasteners holding the assemblies together are particularly susceptible to undetected corrosion beneath the insulation, potentially leading to severe consequences. While various coating products have been employed to mitigate this problem, challenges remain during field application and installation, including high application costs with limited surface preparation, difficulty in coating removal during disassembly, and a lack of publicly available performance data for some coatings under CUI conditions. This study evaluates the corrosion protection performance of three commercially available coatings: a fluoropolymer coating, a nickel-phosphorous coating, and an epoxy phenolic-novolac coating. These coatings were evaluated on threaded fasteners using three standard qualification test methods from ISO 19277 for classification environment CUI-2. Additionally, a field study investigated the long-term durability of the fluoropolymer coating after five years of service under insulation conditions.