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About seamless steel pipe

Seamless steel pipe is widely used.

1. Seamless steel pipes for general purposes are rolled by ordinary carbon structural steel, low alloy structural steel or alloy structural steel, with the largest output. They are mainly used as pipes or structural parts for conveying fluid.

2. There are three types of supply according to different purposes:

a. Supply according to chemical composition and mechanical properties;

b. Supply according to mechanical properties;

c. Supply according to hydrostatic test. If the steel pipe supplied according to class A and B is used to bear liquid pressure, it shall also be subject to hydrostatic test.

3. Seamless pipes for special purposes include seamless pipes for boilers, chemical and electric power, seamless steel pipes for geology and seamless pipes for petroleum.

Seamless steel pipe has hollow section and is widely used as pipeline for conveying fluid, such as pipeline for conveying oil, natural gas, gas, water and some solid materials. Compared with solid steel such as round steel, steel pipe has lighter weight when its bending and torsional strength is the same. It is an economic section steel.

It is widely used to manufacture structural parts and mechanical parts, such as oil drill pipe, automobile transmission shaft, bicycle frame and steel scaffold used in construction. It can improve the material utilization rate, simplify the manufacturing process and save materials and processing hours. It has been widely manufactured with steel pipe.

① Main production process of hot rolled seamless steel pipe (△ main inspection process):
Preparation and inspection of pipe blank △ → heating of pipe blank → piercing → pipe rolling → reheating of steel pipe → sizing (reducing) → heat treatment △ → straightening of finished pipe → finishing → inspection △ (nondestructive, physical and chemical, bench test) → warehousing
② Main production processes of cold rolled (drawn) seamless steel pipe:
Blank preparation → pickling and lubrication → cold rolling (drawing) → heat treatment → straightening → finishing → inspection
The general production process of seamless steel pipe can be divided into cold drawing and hot rolling. The production process of cold-rolled seamless steel pipe is generally more complex than hot rolling. The pipe blank must first be subject to three roll continuous rolling, and the sizing test shall be carried out after extrusion. If the surface does not respond to the crack, the round pipe shall be cut by the cutter, and the blank with a growth of about one meter shall be cut. Then enter the annealing process. The annealing shall be pickled with acid liquid. During pickling, pay attention to whether there are a large number of bubbles on the surface. If there are a large number of bubbles, it means that the quality of steel pipe can not meet the corresponding standard. The appearance of cold-rolled seamless steel pipe is shorter than that of hot-rolled seamless steel pipe. The wall thickness of cold-rolled seamless steel pipe is generally smaller than that of hot-rolled seamless steel pipe, but the surface looks brighter than that of thick wall seamless steel pipe. The surface is not too rough and the diameter is not too many burrs.
The delivery status of hot-rolled seamless steel pipe is generally hot-rolled and delivered after heat treatment. After quality inspection, the hot-rolled seamless steel pipe shall be strictly selected by the staff by hand. After quality inspection, the surface shall be coated with oil, followed by many cold drawing experiments. After hot rolling, the perforation experiment shall be carried out. If the perforation expansion is too large, it shall be straightened and corrected. After straightening, it is transferred to the flaw detector by the conveyor for flaw detection test. Finally, it is labeled and placed in the warehouse after specification arrangement.
Round tube blank → heating → perforation → three roll cross rolling, continuous rolling or extrusion → pipe stripping → sizing (or reducing) → cooling → straightening → hydrostatic test (or flaw detection) → marking → warehousing seamless steel pipe is made of steel ingot or solid tube blank through perforation, and then hot rolled, cold rolled or cold drawn. The specification of seamless steel pipe is expressed in mm of outer diameter * wall thickness.
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 be up to 6mm, 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. Cold rolling has higher dimensional accuracy than hot rolling.
Generally, seamless steel pipes are made of 10, 20, 30, 35, 45 and other high-quality carbon bonded steels, 16Mn, 5mnv and other low-alloy structural steels, or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other bonded steels by hot rolling or cold rolling. 10. Seamless pipes made of low carbon steel such as 20 are mainly used for fluid transmission pipelines. Seamless pipes 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, the strength and flattening test of seamless steel pipe shall be ensured. Hot rolled steel pipes shall be delivered in hot rolling state or heat treatment state; Cold rolling is delivered in heat treated condition.
Hot rolling, as the name suggests, the temperature of rolled piece is high, so the deformation resistance is small and large deformation can be realized. Taking the rolling of steel plate as an example, the thickness of continuous casting slab is generally about 230mm, while after rough rolling and finish rolling, the final thickness is 1 ~ 20mm. At the same time, because the width thickness ratio of the steel plate is small and the requirements for dimensional accuracy are relatively low, the shape problem is not easy to occur, and the convexity is mainly controlled. It is generally realized by controlled rolling and controlled cooling, that is, to control the start rolling temperature and final rolling temperature of finish rolling Round tube blank → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi pass cold drawing (cold rolling) → blank tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → warehousing.

Post time: Apr-24-2022