The article presents the results of comprehensive experimental studies aimed at investigating the relationship between base metal and welding parameters (chemical composition of welded pipes and welding consumables, welding mode), the structure of received weld metal, its basic mechanical properties (strength, ductility and impact strength), and the parameters of static and cyclic cracking strength, used within the force criterion of fracture mechanics. For this purpose, standard and special metal tests have been carried out as well as a study of metal structure after heat treatment over a wide range of cooling rates. The established correlations were confirmed by testing the ring type welded pipe joints and tanks’ steel structures, welded using the most common Transneft technologies. Based on the results obtained, a model has been developed for refining the operability of welded joints according to the initial data of various levels. In particular, the influence of the cooling rate and main parameters of the welded joint metal structure on the change in its basic mechanical properties has been established. In addition, empirical expressions linking a set of mechanical properties (impact strength, relative elongation and proof/ultimate ratio), combined into a complex performance factor, to the metal cracking strength parameters used within the force criterion of fracture mechanics. In order to obtain the greatest practical outcome from the implementation of the developed model, it is proposed to introduce differentiated reduction factors when carrying out strength and durability calculations in accordance with current normative documentation, depending on the level of available data on the welded joint.
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