What is the production process of seamless steel pipe?

1 seamless steel pipe manufacturing technology. Hot rolling (extrusion of seamless steel tube): round tube blank → heating → perforation → three-roll cross rolling, continuous rolling or extrusion → tube stripping → sizing (or reducing) → cooling → straightening → hydrostatic test (or flaw detection) → marking → warehousing 2. Cold drawn (rolled) seamless steel pipe: round tube blank → heating → piercing → upsetting → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → tube blank → heat treatment. In the steel pipe standard, tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indexes, as well as high and low temperature properties required by users are specified according to different application requirements. (1) tensile strength (σb) The maximum force (Fb) borne by the specimen at tensile fracture is the stress (σ) obtained from the original cross-sectional area (So) of the specimen, which is called tensile strength (σb), and the unit is N/mm2(MPa). It represents the greatest ability of metal materials to resist damage under tension. The calculation formula is: where: FB-the maximum force on the specimen when it breaks, n (Newton); So-the original cross-sectional area of the sample, mm2. (2) The yield point (σs) is the stress when the specimen can continue to elongate without increasing the force (keeping the same) during the tensile process, which is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa). Upper yield point (σsu): the maximum stress before the sample yields, and the force drops for the first time; Lower yield point (σsl): the minimum stress at yield stage without considering the initial instantaneous effect. The formula for calculating the yield point is: where: Fs-the yield force (constant) of the specimen in the tensile process, n (Newton) So-the original cross-sectional area of the specimen, mm2. (3) Elongation after fracture (σ) In the tensile test, the percentage of the increased gauge length of the specimen after fracture to the original gauge length is called elongation. It is expressed by σ and the unit is%. The calculation formula is: where: l1-gauge length of the specimen after pulling off, mm; L0-the original gauge length of the sample, mm. (4) Area shrinkage (ψ) In the tensile test, the percentage of the maximum reduction of the cross-sectional area where the diameter of the sample decreases after tensile fracture to the original cross-sectional area is called area shrinkage. Expressed by ψ, and the unit is%. The calculation formula is as follows: where: S0-the original cross-sectional area of the sample, mm2；; S 1-Minimum cross-sectional area at the neck of the specimen after fracture, mm2. ⑤ Hardness refers to the ability of metal materials to resist the surface depression of hard objects, which is called hardness. According to different testing methods and application scope, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. There are three kinds of hardness commonly used in pipelines: Brinell hardness, Rockwell hardness and Vickers hardness. A. Brinell hardness (HB) Press a steel ball or cemented carbide ball with a certain diameter into the surface of the model with a specified test force (f), remove the test force after a specified holding time, and measure the indentation diameter (L) on the surface of the sample. Brinell hardness value is the quotient obtained by dividing the test force by the surface area of the indentation ball. It is expressed by HBS (steel ball) and the unit is N/mm2 (MPa). The calculation formula is: where: f- the test force pressed into the surface of the metal sample, n; D- test steel ball diameter, mm; D—— average indentation diameter, mm. It is more accurate and reliable to measure Brinell hardness, but generally HBS is only suitable for metal materials below 450N/mm2(MPa), not for hard steel or sheet. Brinell hardness is the most widely used in steel pipe standards, and the hardness of this material is often expressed by indentation diameter D, which is intuitive and convenient.