Underwater adhesive bonding for offshore structure maintenance and repair

For maintenance and repair of offshore structures, such as wind turbines, onsite assembly is essential. Currently, secondary elements such as sensors, safety conductor supports, and cathodic protection are welded or screwed to the primary offshore structure, which itself is coated to be protected against maritime stressors such as corrosion induced by sea water. Because of the welding or screwing processes, complex and costly post-treatments are unavoidable for safe operation during the lifetime of the offshore structures. Thus, welding operations for example require the coating to be removed and recoated to provide full corrosion protection. In this study the disadvantages resulting from the state-of-the-art joining processes were addressed in order to be avoided by application of adhesive bonding technology. For this purpose, thermal and mechanical characterisation of two structural two-component (2K) adhesive systems under influence of maritime conditions were carried out. For this purpose, an epoxy adhesive and a methacrylate ester adhesive were analysed. In addition to water absorption and glass transition temperatures, tensile properties as a function of curing were also analysed, as these properties are essential to ensure the reliability and long-term stability of the bond. The adhesive bonds were tested at tensile shear level. Inductive curing of the adhesive was investigated to ensure both adhesive application and removal in a single 30-minute immersion in marine environment. The present work highlights the fundamental challenges of bonding under water in combination with inductive rapid curing of adhesive systems.