OBRABOTKAMETALLOV Vol. 25 No. 4 2023 technology Ta b l e 2 Requirements for mechanical properties of steel for pipelines according to GOST R 53366-2009 (p. 72, Table 6) Class Strength Group Type Total elongation under load, % Yield strength Ri, MPa Strength Rn, MPa, min. Maximum hardness Back wall t hickness t, mm Permissible hardness variation HRC min max HRC HBW 1 H40 – 0.5 276 552 414 – – – – J55 – 0.5 379 552 517 – – – – K55 – 0.5 379 552 655 – – – – K72 – 0.5 491 – 687 – – – – N80 1 0.5 552 758 689 – – – – N80 Q 0.5 552 758 689 – – – – 2 M65 – 0.5 448 586 586 22 235 – – L80 1 0.5 552 655 655 23 241 – – L80 9Cr 0.5 552 655 655 23 241 – – L80 13Cr 0.5 552 655 655 23 241 – – Ta b l e 3 Differences between PSL 1 and PSL 2 pipe materials depending on its chemical composition Chemistry PSL 1 (wt. %) PSL 2 (wt. %) Maximum Carbon content for seamless pipes 0.28 % for ratings ≥ B 0.24 % Maximum Carbon content welded pipes Maximum 0.22 % Maximum Manganese content for seamless pipes 1.40 % for classes ≥ X46 1.40 % for classes ≥ X46 Maximum Manganese content welded pipes 1.40 % for stamps ≥ X46 and ≤ X60; 1.45 % for X65; and 1.65 % for X70 1.40 % for stamps ≥ X46 and ≤ X60; 1.45 % for X65; 1.65 % for Х70; и 1.85 % for X80 Maximum Phosphorus 0.030 % for ratings ≥ A 0.025 % Maximum Sulfur 0.03 % 0.02 % Weldability of pipe steels An additional criterion for pipe steels is the quantitative value of the carbon equivalent. The term “carbon equivalent” (CE) is used to refer to the hardenability or tendency to crack of a steel weld. CE helps to evaluate the cumulative effect of all important alloying elements on the microstructure (formation of the martensitic structure) during welding of steel, since it is the change in the microstructure of steel that determines its properties and behavior after welding. Therefore, a lower CE value is always preferable, which indicates good weldability. The American Petroleum Institute has adopted two equations (CEIIW and CE Pcm) to determine the carbon equivalent limit for API PSL 2 grade pipe steel. The CEIIW equation
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