Calculation Procedures Used for the Substantiation of the System of Requirements for Hull Materials of Marine Structures and Arterial Pipelines

Safe operation of large-size Arctic structures is ensured when the key role is played by the due quality control system applied for shipbuilding and pipeline steels, that is based on special mechanical tests for fracture toughness and cold resistance. The way suggested to substantiate the required test results is calculation allowing to get quantitative estimates while the actual substantiations include subjective reserve factors. Two types of developed calculation procedures are presented in the paper. The first is a probability numeric experiment assessing the required static fracture toughness of the metal of welded joints at the minimum service temperature ordered to ensure the first level of safe operation of welded structures related to brittle crack start resistance. The developed numerical procedure includes a multiple check of the probabilistic fracture condition of a flaw-containing structural element in terms of elastic-plastic fracture mechanics. Supposed distributions of relevant load parameters, temperature and steel performances are developed as well as the corresponding software. The second type of calculation procedures provides for FEM simulations of concurring ductile and brittle fracture in structural elements and specimens of different configurations used in experiments to evaluate various ductile to brittle transition temperatures. The comparison is performed for models where the material has the same critical value of stress intensity factor corresponding to brittle fracture propagation. This ensures the second level of safe operation of structures, namely the resistance to fracture propagation. The principles of FEM simulation and calculation results interpretation are developed. The calculated requirements for ductile to brittle transition temperatures of steels for prospective marine projects with high service parameters cannot be attained with common steel grades, it is proved by the test results collected in NRC Kurchatov Institute – CRISM Prometey. So the calculations undertaken substantiate the area of obligatory application of Arctic steel grades.