How are seamless steel pipes made? What are the theoretical weight specifications of seamless steel pipes?

 　　A steel pipe made of a whole piece of metal with no seams on the surface is called a seamless steel pipe. Seamless steel pipes have a hollow cross-section and are widely used as pipelines for conveying fluids, such as pipelines for conveying oil, natural gas, coal gas, water and certain solid materials. According to the cross-sectional shape, seamless steel pipes are divided into round and special-shaped ones. Special-shaped pipes have square, oval, triangle, hexagon, melon seed, star, winged pipes and many other complex shapes. The following is a complete table of theoretical weights of seamless steel pipes, seamless steel pipe sizes and allowable deviation tables.

　　How are seamless steel pipes made?

　　1. Main production process of hot-rolled seamless steel pipes (△ Main inspection process):

　　Pipe blank preparation and inspection△→Pipe blank heating→Pipe perforation→Pipe rolling→Steel pipe reheating→Sizing (reducing) diameter→Heat treatment△→Finished pipe straightening→Finishing→Inspection△(Non-destructive, physical and chemical, bench inspection)→Warehousing

　　2. Main production process of cold-rolled (drawn) seamless steel pipes:

　　Blank preparation→Acid pickling and lubrication→Cold rolling (drawing)→Heat treatment→Straightening→Finishing→Inspection

　　General seamless steel pipe production process can be divided into cold drawing and hot rolling. The production process of cold-rolled seamless steel pipe is generally more complicated than hot rolling. The pipe blank must first be rolled with three rollers, and then the sizing test must be carried out after extrusion. If there is no response crack on the surface, the round pipe must be cut by a cutting machine and cut into a billet of about one meter in length. Then enter the annealing process. Annealing should be pickled with acidic liquid. When pickling, pay attention to whether there is a large amount of bubbles on the surface. If there is a large amount of bubbles, it means that the quality of the steel pipe does not meet the corresponding standards. In appearance, cold-rolled seamless steel pipes are shorter than hot-rolled seamless steel pipes. The wall thickness of cold-rolled seamless steel pipes is generally smaller than that of hot-rolled seamless steel pipes, but the surface looks brighter than thick-walled seamless steel pipes, and the surface is not too rough, and the diameter does not have too many burrs.

　　Seamless steel pipe

　　The delivery state of hot-rolled seamless steel pipes is generally hot-rolled and heat-treated before delivery. After quality inspection, hot-rolled seamless steel pipes must be strictly hand-selected by staff, and the surface must be oiled after quality inspection, followed by multiple cold drawing tests. After hot rolling treatment, perforation tests must be carried out. If the perforation diameter is too large, straightening and correction must be carried out. After straightening, it is transported to the flaw detector by the conveyor for flaw detection testing, and finally labeled, arranged in specifications, and placed in the warehouse.

　　Round tube billet → heating → perforation → three-roller oblique rolling, continuous rolling or extrusion → tube removal → sizing (or reducing diameter) → cooling → straightening → hydraulic pressure test (or flaw detection) → marking → storage Seamless steel pipe is made of steel ingot or solid tube billet by perforation into rough tube, and then made by hot rolling, cold rolling or cold drawing. The specifications of seamless steel pipe are expressed by outer diameter * wall thickness in millimeters.

　　The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-200mm. The outer diameter of cold-rolled seamless steel pipe can reach 6mm, the wall thickness can reach 0.25mm, and the outer diameter of thin-walled pipe can reach 5mm and the wall thickness is less than 0.25mm. Cold rolling has higher dimensional accuracy than hot rolling.

　　Common seamless steel pipes are made of 10, 20, 30, 35, 45 high-quality carbon steel, 16Mn, 5MnV and other low-alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other alloy steels hot rolled or cold rolled. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid delivery pipelines. Seamless pipes made of medium carbon steel such as 45 and 40Cr are used to manufacture mechanical parts, such as load-bearing parts of automobiles and tractors. Generally, seamless steel pipes must ensure strength and flattening tests. Hot-rolled steel pipes are delivered in hot-rolled or heat-treated states; cold-rolled steel pipes are delivered in heat-treated states.

　　Hot rolling, as the name implies, has a high temperature for the rolled piece, so the deformation resistance is small and a large deformation amount can be achieved. Taking the rolling of steel plates as an example, the thickness of the continuous casting billet is generally about 230mm, and after rough rolling and finishing rolling, the final thickness is 1~20mm. At the same time, due to the small width-to-thickness ratio of the steel plate, the dimensional accuracy requirements are relatively low, and it is not easy to have plate shape problems, mainly to control the convexity. For those with organizational requirements, it is generally achieved through controlled rolling and controlled cooling, that is, controlling the starting rolling temperature and final rolling temperature of finishing rolling. Round tube billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multiple passes of cold drawing (cold rolling) → billet tube → heat treatment → straightening → water pressure test (flaw detection) → marking → storage.