A joint industrial program (JIP), termed “Seamless 100 ksi weldable” was launched in order to address the complex design issues of high strength Q&T seamless pipes for ultra deep water applications. The JIP was split in two main phases, the first one devoted to the development and production of seamless pipes, with minimum yield strength of 90 ksi (620 MPa) to 100 ksi (690 MPa), and the second one to evaluate their field weldability. Phase I was recently completed. The role of chemical composition and Q&T process conditions on microstructure and precipitation was analyzed, together with relevant effects on strength and toughness, for both laboratory and industrial steels. The main microstructural features which control the strength-toughness combination of these high strength Q&T steel grades were identified and results were exploited for the set-up of a production route for pipelines and risers. The 100 ksi grade was achieved in 16 mm (0.630 in) and 25 mm (0.980 in) WT pipes. Phase II is in progress.

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