TMCP Steel for Offshore Structures: Part Two

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Generally, offshore structural steels require superior low temperature toughness for the base metal and the welded joints in view of the need for prevention of brittle failure. Of particular importance are Charpy impact properties, but also CTOD (crack tip opening displacement) properties subject to the local brittle zones (hereinafter referred to as ‘LBZ’) are also of high importance. Therefore, the establishment of high toughness and high strength through fining the microstructure of HAZ (heat affected zone), and the reduction of LBZ or the suppression of its creation has been a one of the major issues of recent times.

Dillinger Hütte GTS supplies heavy plate conforming to all widely used standards, including EN 10225, BS 7191, API and NORSOK. The range of grades available extends from normalized, via water-quenched and tempered, up to and including TMCP steels. The outstanding mechanical strengths and associated toughness of these materials meet even the most demanding specifications for offshore structures used in the North Sea. But what makes these steels true high-tech materials is the combination of these properties with optimum workability, and above all, cold-workability and weldability. Please see the table of materials.

As an illustration in the tables below you will find a comparison of the steel grade 355 under delivery conditions normalized (N) and thermo mechanically rolled (TMCP) comparing in detail, the tensile and yield strength and toughness properties of each delivery condition.

 

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Table 1: Grade 355N - comparison of tensile strength, yield strength and toughness

 

 

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Table 2: Grade 355 TMCP – comparison of tensile strength, yield strength and Toughness