The trend for development of large offshore structures requires raising tensile properties of steel without incurring detrimental effects on toughness and weldability. Our long experience in the field of high strength low alloyed steels, and the availability of experimental data on the relationship between weldability, fracture mechanics and chemical composition has enabled GTS industries to develop new TMCP (ThermoMechanical Controlled Process) plates of the API 2 W Grade 60 type, with excellent toughness and weldability properties.
North sea offshore structures have been built by using 50 ksi Y.s. [355 N/mm2] normalized steel materials. Although these materials have shown good weldability and good toughness in the Heat Affected Zone, the future development of large offshore structures will require more sophisticated and reliable higher strength material allowing the operator to take advantage of : - Weight reduction, prefabrication, fabrication, installation cost reduction … (Figures 1 & 2). Deeper sea oil and gas reservoirs operation areas with larger structures using new conceptual design (i.e. : dead weight reduction of the hull and topside of the tension leg platform). In this instance, GTS Industries has developed offshore structural plates in the range of 5 mm up to 80 mm wall thickness which complies with the API 2W Grade 60 [Y.S. 420 N/mm2]. The chemical analysis displays a very low carbon equivalent content, low Silicon content, Titanium addition and alloy element modification comparable to the analysis of the well known API 2H Grade 50 [Y.S. 355 N/mm2] normalized plates. Weldability of the Y.S. 420 has been thoroughly examined against the most severe requirement and particularly applicable to material intended for North Sea (BSI 7191) and Gulf of Mexico applications (API RP 2Z).
