Seamless steel pipes are perforated from a whole round steel, and the steel pipes without welds on the surface are called seamless steel pipes.
Classification of seamless pipes:
According to the production method, seamless steel pipes can be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and top pipes.
According to the cross-sectional shape, seamless steel pipes are divided into round and special-shaped. Special-shaped pipes have square, elliptical, triangular, hexagonal, melon seed, star, and finned pipes. The maximum diameter is 900mm and the minimum diameter is 4mm.
According to different purposes, there are thick-walled seamless steel pipes and thin-walled seamless steel pipes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemical industry, boiler pipes, bearing pipes, and high-precision structural steel pipes for automobiles, tractors, and aviation.
Use of seamless steel pipe:
1. General-purpose seamless steel pipes are rolled by ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, with the largest output, and are mainly used as pipelines or structural parts for conveying fluids.
2. According to different purposes, seamless pipes are supplied in three categories:
a. Supply according to chemical composition and mechanical properties;
b. According to mechanical performance;
c. According to the water pressure test supply. Steel pipes supplied according to categories a and b. if used to withstand liquid pressure, shall also undergo a hydraulic test.
3. Special-purpose seamless pipes include seamless pipes for boilers, chemical and electric power, seamless steel pipes for geology, and seamless pipes for petroleum.
Seamless steel pipes have a hollow section and are used in large quantities as pipelines for conveying fluids, such as pipelines for conveying oil, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, steel pipe has lighter weight when the bending and torsion strength is the same, and it is an economical section steel.
It is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. Working hours.
Production process of seamless steel pipe:
①Main production process of hot-rolled seamless steel pipe:
Tube billet preparation and inspection△→tube billet heating→perforation→tube rolling→steel pipe reheating→sizing→heat treatment△→finished pipe straightening→finishing→inspection
②Main production process of cold-rolled seamless steel pipe:
Blank preparation → pickling and lubrication → cold rolling → heat treatment → straightening → finishing → inspection
The production process of general seamless steel pipes can be divided into two types: cold-drawn and hot-rolled. The production process of cold-rolled seamless steel pipes is generally more complicated than that of hot rolling. The tube billet must first be subjected to three-roll continuous rolling, and then it must be processed after extrusion. In the sizing test, if the surface does not respond to cracks, the pipe will be cut by a cutting machine and cut into a blank of about one meter in length. Then enter the annealing process. Annealing needs to be pickled with acidic liquid. When pickling, pay attention to whether there is a lot of blistering on the surface. If there is a lot of blistering, 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. Much rough, without too many burrs.
The delivery state of hot-rolled seamless steel pipes is generally hot-rolled and delivered after heat treatment. After the quality inspection, the hot-rolled seamless steel pipes must be strictly hand-selected by the staff. After the quality inspection, the surface must be oiled, and then followed by multiple cold drawing experiments. After the hot-rolling treatment, the piercing experiment must be carried out. , If the perforation is too large, it must be straightened. After straightening, it is transferred by the conveyor to the flaw detector for flaw detection experiment. Finally, the label is affixed, the specification is arranged, and then it is placed in the warehouse.
Round tube blank → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → pipe removal → sizing (or reducing) → cooling → straightening → hydraulic test (or flaw detection) → marking → warehousing
Seamless steel pipes are made of steel ingots or solid tube billets through perforation into capillary tubes, and then made by hot rolling, cold rolling or cold drawing. The specification of seamless steel pipe is expressed by outer diameter * wall thickness (mm). 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 pipe can be up to 6mm and the wall thickness can be up to 0.25mm. The outer diameter of thin-walled pipe can be up to 5mm and the wall thickness is less than 0.25mm. Rolling has higher dimensional accuracy than hot rolling.
Generally, seamless steel pipes are made of high-quality carbon steels such as No. 10, 20, 30, 35, 45 and other low-alloy structural steels such as 16Mn, 5MnV, or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other composite steels by hot rolling or cold rolling. . Seamless pipes made of low-carbon steel such as No. 10 and No. 20 are mainly used for fluid transportation pipelines. Seamless tubes made of medium carbon steel such as 45 and 40Cr are used to manufacture mechanical parts, such as stressed parts of automobiles and tractors. Generally, seamless steel pipes should be used for strength and flattening tests. Hot-rolled steel pipes are delivered in hot-rolled state or heat-treated state; cold-rolled steel pipes are delivered in heat-treated state.
The hot rolled product has a high temperature, so the deformation resistance is small, and a large amount of deformation can be achieved. Taking the rolling of steel plate 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 the shape problem is not prone to occur, and the crown is mainly controlled. The requirements for the organization are generally achieved through controlled rolling and cooling, that is, controlling the start-rolling temperature and final rolling temperature of finishing rolling.
Round tube blank → heating → piercing → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → blank tube → heat treatment → straightening → hydraulic test (flaw detection) → marking → warehousing