Steel pipes made of a single piece of metal with no seams on the surface are called seamless steel pipes. Seamless steel pipes have hollow sections and are widely used as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, coal gas, water and certain solid materials.
Steel pipes made of a single piece of metal with no seams on the surface are called
seamless steel pipes. Seamless steel pipes have hollow sections and are widely used as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, coal gas, water and certain solid materials. According to the cross-sectional shape, seamless steel pipes are divided into two types: round and special-shaped. Special-shaped pipes have square, oval, triangle, hexagonal, melon-shaped, star-shaped, and finned pipes in various complex shapes. Below is a complete table of theoretical weights of seamless steel pipes, sizes and allowable deviations of seamless steel pipes.
How to make seamless steel pipe
1. Main production processes of hot-rolled seamless steel pipes (△Main inspection processes):
Preparation and inspection of tube blank △ → heating of tube blank → perforation → pipe rolling → steel pipe reheating → diameter determination (reduction) → heat treatment △ → finished pipe straightening → finishing → inspection △ (non-destructive, physical and chemical, Taiwan inspection) → warehousing
2. The main production processes of cold-rolled (drawn) seamless steel pipes:
Blank preparation→pickling and lubrication→cold rolling (drawing)→heat treatment→straightening→finishing→inspection
The production process of general seamless steel pipes can be divided into two types: cold drawing and hot rolling. The production process of cold-rolled seamless steel pipes is generally more complicated than hot rolling. The tube blanks must first be subjected to three-roll continuous rolling, and then extruded. After the sizing test, if there is no response crack on the surface, the round 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 requires pickling with acidic liquid. When pickling, pay attention to whether there is a large amount of bubbling on the surface. If there is a large amount of bubbling, it means that the quality of the steel pipe cannot 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 hot-rolled seamless steel pipes, but the surface looks brighter than thick-walled seamless steel pipes, and the surface is not too thick. It's quite rough, and there aren't many burrs in the diameter.
Seamless steel pipe
The delivery state of hot-rolled seamless steel pipes is generally in a hot-rolled state after heat treatment. After passing the quality inspection, the hot-rolled seamless steel pipe must undergo strict manual selection by the staff. After the quality inspection, the surface must be oiled, followed by multiple cold-drawing experiments. After the hot-rolling treatment, a perforation experiment must be performed. , if the diameter of the perforation is too large, it needs to be straightened and corrected. After straightening, it is transferred by the transmission device to the flaw detection machine for flaw detection experiments. Finally, it is labeled, arranged in specifications, and placed in the warehouse.
Round tube blank → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → straightening → hydraulic test (or flaw detection) → marking → warehousing seamless steel pipe It is made of steel ingots or solid tube blanks through perforation and then hot-rolled, cold-rolled or cold-drawn. The specifications of seamless steel pipes are expressed in terms of outer diameter * wall thickness in millimeters.
The outer diameter of hot-rolled seamless steel pipes is generally greater than 32mm and the wall thickness is 2.5-200mm. The outer diameter of cold-rolled seamless steel pipes can be up to 6mm and the wall thickness can be up to 0.25mm. The outer diameter of thin-walled pipes can be up to 5mm and the wall thickness is less than 0.25mm. Rolling has higher dimensional accuracy than hot rolling.
General seamless steel pipes are made of hot-rolled or cold-rolled high-quality carbon structural steels such as 10, 20, 30, 35, 45, 16Mn, 5MnV and other low-alloy structural steels, or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other composite steels. Seamless pipes made of 10 and 20 grade low carbon steel 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 must ensure strength and flattening tests. Hot-rolled steel pipes are delivered in a hot-rolled or heat-treated state; cold-rolled steel pipes are delivered in a heat-treated state.
Hot rolling, as the name suggests, has high temperature, so the deformation resistance is small and large deformation can be achieved. Take the rolling of steel plates as an example. Generally, the thickness of continuous casting billet is about 230mm, and after rough rolling and finish 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 plate shape problems are not prone to occur. The main focus is to control the crown. For those with structural requirements, it is generally achieved through controlled rolling and cooling, that is, controlling the opening rolling temperature and final rolling temperature of finishing rolling. Round tube blank → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → hydrostatic test (flaw detection) → marking → entering library.
Note: The formula for calculating the theoretical weight of commonly used profiles:
m=F×L×ρ
m—mass Kg; F—cross-sectional area m2; L—length m; ρ—density*Kg/m3
☆Among them: F cross-sectional area calculation method:
1. Square steel F= a2
2. Steel pipe F=3.1416×$(D-$) D—diameter $—thickness
3. Steel plate, flat steel F= a×$ a—width
density:
Steel: 7.85*103 kg/m3
Aluminum: 2.5～2.95*103
Copper: 8.45～8.9*103
Cast iron: 6.6～7*103
