Assembling bolted joints under water: Influence of a surrounding medium on bolt preload and slip factor

Due to recent failures of high-strength steel bolts that were assembled in the splash zone and the submerged zone of offshore structures, the applicability of European steel construction standards regarding subsea use was investigated. It was found, that Eurocode 3 and EN 1090-2 do not cover specific requirements for the installation of bolts under water. The influence of water on tightening, bolt preload and slip factor of faying surfaces were examined using special testing equipment. Different tightening me-thods and alternative washer systems were applied. Lubrication of bolts used according to the standards mentioned does not seem suitable for underwater application. Self-loosening and bolt overload are potential risks that come with under water installation of corresponding bolt assemblies. Design surface class of faying surfaces could be verified under water, but failure behavior was different when tested under water compared to regular testing conditions.