ENABLING AN OPTIMISED HIGH STRENGTH STEEL PRESSURE HULL BUILD STRATEGY BY THE USE OF UNDER-MATCHED WELDS

摘要

Recent classes of UK naval submarine pressure hulls have been designed and built using quenched and tempered high strength Q1(N) steel with matching weld consumables. To increase operational capability for future designs the UK MOD has been investigating the use of higher strength steels. Construction in such steels brings the need for stringent process controls to avoid the potential for weld defects; in particular hydrogen cracking. The use of "under-matched" welding consumables (where the filler has a lower tensile strength compared with the parent metal) to mitigate this risk has been advocated across a number of sectors even though it goes against welding norms. For such a practice to be approved for UK naval vessels, in particular submarines, the consequences of such a change from tradition need to be understood. This paper describes recent MOD trials to provide a body of evidence to make a case for such approval.