OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 However, the analysis shows that the current standard requirements for the ultimate tensile strength of the weld are usually based on the lower ultimate tensile strength of the pipe. Please note that this requirement is aimed at achieving high strength of the butt circumferential welds of the pipeline. In this case, the fracture of test specimens at the welding site will lead to the welding of circumferential welds in conditions of insufficient strength. Under such circumstances, the lower ultimate tensile strength of the base material will be unreasonably used as a requirement for evaluating the ultimate tensile strength of circumferential welds [40], confirming that the current requirements for the ultimate tensile strength of circumferential welds cannot fully ensure the necessary safety of pipeline systems. In addition, the requirements for the ultimate tensile strength of the weld found in the current specifications and standards are not proposed to meet certain requirements for deformation of circumferential welds. The requirements for deformation of pipelines crossing different landscapes and geological hazards can be completely different. Therefore, the ultimate tensile strength requirements of circumferential welds should be developed and determined in accordance with various situations of deformation requirements [42–50]. Ta b l e 6 Tensile strength requirements for weld metal in various specifications and standards Documents Ultimate tensile strength requirement ISO 13847; API 1104; AS/ NZS 2885.2:2020; DEP 31.40.20.37-GEN If the specimen is destroyed in the welding or fusion zone, then the observed strength should be above or equal to σu of the pipe material, and also meet the strength requirements. If the specimen is destroyed outside of both the weld and the heat affected zone (HAZ), the strength should be at least 95 % of the strength σu of the pipe material. CSA Z662 The ultimate tensile strength of the test specimen should be above or equal to σu of the base metal or 95 % σu of the base metal, if the fracture occurs outside the weld and HAZ. GB/T 31032 If the specimen is destroyed in the welding or fusion zone, and the observed strength should be above or equal to σu of the pipe material and meet the strength requirements. When the specimen is destroyed outside the weld and the HAZ, the strength should be at least σu of the pipe material. RD 26-11-08-86 Welded joints. Mechanical tests. The overall test result is considered unsatisfactory if at least one of the specimens showed a result that differs from the established standards (downward): in terms of ultimate tensile strength – by more than 10 %; in terms of impact strength – by more than 0.5 kgf×m/cm2 (0.05 MJ/m2). These provisions remain valid even if the arithmetic mean of the test results corresponds to the standard indicators. GOST 31447-2012 Steel welded pipes for trunk gas pipelines, oil pipelines and oil products pipelines. Specifications. The ultimate tensile strength of the pipes welds of all types when testing a flat specimen with removed excess weld metal or flash should be at least equal to the value of σu for the base metal. The maximum actual values of the ultimate tensile strength σu should not exceed the established standards by more than 108 MPa for strength classes up to K55 and more than 98 MPa for strength classes K55 and more. SNiP III-42-80: Main pipelines. The ultimate tensile strength of the welded joint, determined on discontinuous specimens with removed excess weld metal, should not be less than the standard value of the ultimate tensile strength of the metal of the pipes. GOST 32569-2013 Industrial steel pipe-lines. Requirements for design and operation in explosive and chemically dangerous industries. The minimum standards of mechanical properties of welded joints should not be lower than the lower value of the ultimate tensile strength of the base metal according to the standard or technical specifications for this steel grade.
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