Speaker
Description
The energy production of the future will be dominated by CO2-emission free techniques like wind turbines and become essential in scope of the planned hydrogen economy. As onshore installation capacity is limited, the increase of the number of offshore wind turbines (OWT) is a major goal. In that connection, the OWTs continously increase in size and weight and demand adequate foundations concepts like monopiles or tripods. These components are typically manufactured from welded mild steel plates with thickness up to 200 mm. The predominant welding technique is submerged arc welding (SAW) with up to five wires. In accordance to the standards, the occurrence of delayed hydrogen assisted cracking is anticipated by either a hydrogen removal heat treatment (HRHT) or a so-called minimum waiting time (MWT) before non-destructive testing (NDT) of the respective weld joint is allowed. The reason for the MWT is the necessary time for the hydrogen diffusion at ambient temperature due the high plate thickness. Both the effectiveness of a HRHT at elevated temperatures or the MWT at ambient temperature can be estimated by calculation of the diffusion time. This time depends on reliable hydrogen diffusion coefficients and these are rare in literature. For that reason, this study presents the hydrogen diffusion coefficents obtained from a multi-layer SAW joint of an offshore steel grade. Two different experimental technqiques were used to identfy the respective diffusion behavior: (1) hydrogen desportion experiments with a carrier gas hot extraction analyzer at elevated temperatures for the characterization of a HRHT and (2) the electrochemical permeation technique at ambient temperature for the characterization of a MWT. From both experiments, the respective diffusion coeffients were calculated. The obtained coefficients are different from those reported in literature, i.e. the duration or applicability of a HRHT or MWT must be critically discussed.
| Speaker Country | Germany |
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