One Step Further: 500 MPa Yield Strength Steel for Offshore Constructions

Abstract

Essential savings in time and money can be achieved if the topside of an offshore platform can be installed in a single piece. For the projects Grane and Valhall located in the North Sea this goal could only be met by using steels with a minimum yield strength of 500 MPa. At the same time the steel should be as easily weldable as the 420 MPa TMCP steel that had become a common offshore steel grade in Norway during the last decade. Based on profound experience in TMCP and research programmes on weldability a chemical composition was selected promising to scope the requirements for base material and HAZ. A few plates were first produced and tested successfully. Excellent weldability in terms of HAZ toughness and low preheat was proven through a vast qualification programme and test welds at the yards. In the first part of the 3500 t order for Valhall the process parameters were optimised to achieve stable properties for the whole thickness range from 15 to 80 mm. The development of this steel grade S500M3z, the results and experience gained on the first deliveries shall be presented in the paper.