60 mm thick submerged arc weld joint. Thick weld joints mean prolonged time for hydrogen diffusion into critical regions. The possible cracking is delayed and must be anticipated by a waiting time before NDT is conducted.
Source: BAM, division Weld Mechanics
Offshore wind turbines (OWT) are a major goal of the energy strategy of Germany encompassing the increase of the installed wind power. OWT components are manufactured from welded steel plates with thicknesses up to 200 mm. The underlying standards and technical recommendations for construction of OWTs encompass specifications of so-called minimum waiting time (MWT) before non-destructive testing of the weld joints is allowed. Reason is the increased risk of time-delayed hydrogen-assisted cold cracking as hydrogen diffusion is very slow due to the very thick plates. The strict consideration of those long MWT up to 48 h during the construction of OWTs leads to significant financial burden (like disproportionately high costs for installer ships as well as storage problems (onshore)). In this study, weld joints made of S355 ML were examined in comparison with the offshore steel grade S460 G2+M. The aim was to optimize, i.e., reduce, the MWT before NDT considering varied heat input, hydrogen concentration and using self-restraint weld tests. This would significantly reduce the manufacturing time and costs of OWT construction. To quantify the necessary delay time until hydrogen-assisted cold cracks appear, acoustic emission analysis was applied directly after welding for at least 48 h.
Waiting time before NDT of welded offshore steel grades under consideration of delayed hydrogen-assisted cracking
Eugen Wilhelm, Tobias Mente & Michael Rhode
published in Welding in the World, Vol. 65, pages 947–959, 2021
BAM division Weld Mechanics