OBRABOTKAMETALLOV technology Vol. 25 No. 4 2023 HSLA steels usually contain very low carbon content and a small amount of alloying elements [1, 2, 14], and are classified by the American Petroleum Institute (API) in order of its strength (X-42, X-46, X-52, X-56, X-60, X-65, X-70, X-80, X-100 and X-120). These properties are achieved by careful selection of Miroslav’s composition and optimization of thermal and mechanical treatment (TMT) and accelerated cooling conditions after TMT. Specifications concerning chemical composition, mechanical properties and other important aspects such as welding, cutting, manufacturing, etc. of oil and gas piping materials are determined by the American Petroleum Institute (API), the International Organization for Standardization (ISO) and other national agencies [4–9]. Requirements for pipe steel of strength class K55 according to GOST R 53366-2009 The chemical composition (table 1) of steels is limited only by the content of harmful impurities – the content of sulfur and phosphorus should be no more than 0.030 wt. % (P ≤ 0.030, S ≤ 0.030). In addition, when tested in tension, steels should have a yield strength (σy) equal to 379–552 MPa and an ultimate strength (σu) above or equal to 655 MPa (table 2). Requirements for pipe steel of strength class K55 According to API requirements, piping materials are manufactured or supplied with two levels of product specification, known as PSL 1 and PSL 2. According to API 5L specification, PSL 1 pipes are supplied with grades A25, A25P, A, B, X42, X46, X52, X56, X60, X65 and X70, while PSL 2 pipes are supplied with grades B, X42, X46, X52, X56, X60, X65, X70, X80, X90, X100 and X120. It is also worth noting that there is no carbon equivalent limit for PSL 1 pipes. Another significant difference is based on the type of pipe ends. PSL 1 pipes can be manufactured and supplied with smooth ends, threaded ends, sockets and as a special connecting pipe, whereas PSL 2 pipes are manufactured only with smooth ends. In this document, information on the chemical composition, mechanical properties and the pipe manufacturing technologies used is indicated for pipe steel from X42 to X120. The original grades A25, A25P, A and B are excluded from the main discussion, since these grades are considered medium-strength materials. According to the American Society of Metals (ASM), low-alloy steel with a yield strength of at least 290 MPa is considered a high-strength steel. Knowledge of the chemical composition and mechanical properties of these pipes is necessary to understand the weldability and other aspects of welding these pipes. Requirements for chemical composition according to API 5CT are limited only to the content of harmful impurities – the content of sulfur and phosphorus should be no more than 0.030 wt. % (P ≤ 0.030, S ≤ 0.030). The difference in chemical composition requirements between PSL 1 and PSL 2 is shown in table 3. Ta b l e 1 Chemical composition of pipelines steel according to GOST R 53366-2009 (p. 71, Table 5) Class Strength Group type Mass content of element, % C Mn Mo Cr Ni Cu P S Si min max min max min max min max min max min max min 1 H40 – – – – – – – – – – – 0.030 0.030 – J55 – – – – – – – – – – – 0.030 0.030 – K55 – – – – – – – – – – – 0.030 0.030 – K72 – – – – – – – – – – – 0.030 0.030 – N80 1 – – – – – – – – – – 0.030 0.030 – N80 Q – – – – – – – – – – 0.030 0.030 –
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