JULY 202319concept to ease fabrication, improve weldability and reduce the risk for cracking. Using purely martensitic alloys showed the above-described difficulties during fabrication at the shipyards leading to Vallourec developing a bainitic alloy which has by its nature a higher toughness compared to the martensitic ones. Vallourec went through an extensive approval program, for which the mill in Düsseldorf gained as first seamless pipe mill to be qualified according to ABS and DNV standards down to -60°Cfor steel with yield strength of 690MPa/100ksi.WeldabilityThe bainitic alloy concept developed by Vallourec has a typical carbon equivalent (in accordance to IIW formula) of 0.55%, a critical metal parameter (Pcm) of 0.25% and a carbon equivalent in accordance to Thyssen formular (CET) of 0.33%. Whereas the common, pure martensitic alloys have typically slightly higher carbon equivalents and Pcm´s coming from the in general higher carbon content. This higher carbon content is the most important driver to differentiate between Zone III and Zone I of the Graville diagram [Graville] by evaluating the preheating temperature of AWS D1.1 (ref). Vallourec's newly developed bainitic X100 (Vallourec´s proprietary grade Oceanfit® 100 WeldFIT) belongs to Zone I which states that cracking is unlikely and that the pure martensitic alloys are present in Zone III which is the worst Zone as it requires the previously described precautions. Lab and in field trials with customers confirmed that the new Vallourec X100 is weldable without preheating and without PWHT, offers significant savings due to higher weld deposit rate, a wider range of fabrication as well as less rework of material related cracking. Find further details at Strötgen[et. al.].Vallourec supports by its new developments the path to become a faster low carbon society and is able to contribute to lower the total cost of ownership and helps to reduce the levelized costs for offshore wind.Graville, B. (1986) A survey review of weld metal hydrogen cracking.Weld World, 24 (9/10), 190­198.Strötgen, D., Gourment, A., Hojda, R.(2021) "Welding performance of high strength X100Q / S690QLHHO seamless pipes without preheating for offshore structural applications" Proceedings of The 31st International Ocean and Polar Engineering Conference, Rhodes, Greece, June 2021. Figure 1 ­ Charybdis WTIVFigure 2 ­ Graville Diagram [Graville]
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