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Seamless pipe means

A seamless pipe is a tube that does not have any welding seam. Seamless pipes are derived from solid steel that is in sheet or bar form and is formed into a solid round shape known as “billets” which are then heated and cast over a form such as a piercing rod to create a hollow tube or shell.A seamless tube may also be known as a seamless pipe.

Characteristics of seamless steel pipe
Seamless steel pipe for the use of engineering and construction is very widely, it is a hollow steel strip no seams, it is mainly used to transport liquids pipelines, different look and general steel,one of those heavy type steel, it has a strong resistance to corrosion, resistant to general corrosion.
Will not rust, this performance makes seamless steel tubes extend the life, the most important is that it is very clean and no toxins.
Compared with other plastic seamless steel pipe having strong mechanical resistance, impact regardless of how high a temperature is not interested in the use of seamless steel pipe, it is mounted and the other pipe is the same, can replace other piped water and other liquids.


Characteristics of seamless steel pipe
High precision can do small batch production.
Smaller diameter.
Weldability strong, high compression capability.
Steel pipe superior performance, relatively dense metal.
Steel Cross area is more complex.
High precision cold drawn products, good surface quality.
Classification of Seamless Steel Pipe
According to the manufacturing process, seamless pipe can be divided into hot-rolled seamless steel tubes and cold-drawn seamless steel pipe two kinds. Cold drawn tube is also divided into circular pipe and shaped pipe.

Hot-rolled seamless steel pipe
Hot rolled is relative to the cold-rolled, cold rolling is below the recrystallization temperature of the rolling, and hot rolled is carried out at above the recrystallization temperature of the rolling.

Advantages
hot rollded seamless steel pipe can damage the cast microstructure of the steel ingot, refinement of the crystal grains of the steel, and eliminate the defects of the microstructure, so that the the steel organization compacting, improve the mechanical properties. This improvement is reflected in the rolling direction, so that the steel is no longer to a certain extent isotropic; pouring the formation of bubbles, cracks, and osteoporosis, under high temperature and pressure can also be welded together.

Disadvantages:
1 After the hot rolling, the nonmetallic inclusions in the interior of a steel (mainly sulfides and oxides, as well as the silicate) was pressed into a sheet, stratified (laminated) phenomenon appears. The layering of the steel in the thickness direction by the pull performance deteriorated significantly, and may appear in the weld shrinkage interlayer tear. Weld shrinkage induced local strain often reach several times the yield point strain, the strain is much greater than the load caused;
2 Residual stress caused by uneven cooling. The residual stress is the stress of internal self-phase equilibrium in the absence of external force, the hot-rolled steel of various cross-sectional has a residual stress such Usually steel sectional dimension is the greater, the greater the residual stresses. Residual stress is self-phase equilibrium, but the steel members in the performance external force or have a certain influence. Such as deformation, stability, anti-fatigue may adversely.
3 Hot-rolled steel products, poor control of thickness and edge width. We are familiar with the thermal expansion and contraction, even if the beginning of the hot-rolled out are standard length, thickness, or there will be some negative final after cooling, this negative differential edge width wider the increasing thickness of the performance of the more obvious.
So for large steel for steel edge width, thickness, length, angle, and sideline no law requires too precise.

Cold rolled seamless pipes
Cold rolled seamless pipes are cold drawn or cold rolled precision seamless steel pipes with high accuracy of the dimension and good finish of the surface used for the machinery and hydraulic equipment. The cold rolled process refers to the method adopted to process the steel plates or strips into various types of steel products by cold working processes such as the cold bend and cold drawn processes. Cold rolled seamless pipes not only include general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking steel pipes, but also include carbon steel pipes with thin walls, alloy steel pipes with thin walls, stainless steel pipes with thin walls and special-shaped steel pipes. The hot rolled seamless pipes usually have outer diameter larger than 32mm and wall thickness between 2.5mm to 75mm; the cold rolled seamless pipes usually have the outer diameter less than 6mm and wall thickness less than 0.25 mm; the thin-wall pipes usually have the outer diameter less than 5mm and wall thickness less than 0.25mm. The cold rolled pipes generally have the high dimensional accuracy than the hot rolled pipes.

Advantages and disadvantages of cold rolled seamless pipes
Advantages
1. The speed of molding and the productivity are high. The coating will not be damaged. The sections can be made in various shapes so as to adapt to different conditions. Cold rolled processes can make steel have great plastic deformation so as to increase the yield point of steel.
2. Cold rolled processes can destroy the casting structure of steel ingots, refine the grain of steel products and eliminate the defects of microstructure so as to make the structure of steel products compact and improve the mechanical property of steel products. This kind of improvement reflects mainly along the rolling direction, which makes steel products not isotropic bodies any longer to some extent. Bubbles, cracks and shrinkage formed in casting can be repaired under the effects of high temperatures and pressure.
Disadvantages
1. The section of cold rolled steel is the open section generally, which has relatively low free torsion stiffness. The steel is twisted easily when it is bent; flexural-torsional buckling showed up easily when steel is pressed. The torsion resistance is relatively poor.
2. The wall of the cold rolled steel pipe is relatively thin. The corners connecting plates are not thickened. The bearing ability of the partial concentrated load is weak.

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