A seamless steel pipe is a circular pipe having a hollow section and no seams around it. The seamless steel pipe is made of carbon steel, alloy steel, stainless steel ingot or solid tube blank, and then is made by hot rolling, cold rolling or cold drawing. Seamless pipes are considered superior to welded pipes as they are built using monolithic steel billets, with intrinsic mechanical strength, without seam welds.

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 ARE AS FOLLOWS:

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.

Carbon Steel Pipes

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.

Seamless steel pipes is divided into the following categories because of different purposes:

seamless steel pipe for structure is mainly used for general structure and mechanical structure.  Transmission fluid with seamless steel tubes is mainly used for the transmission fluid on pipeline projects and large equipment.  Low and medium pressure boiler seamless steel pipe is used in manufacturing a variety of structures for low and medium pressure boiler superheated steam pipes, boiling water tube and locomotive boilers, superheated steam pipe, opium pipe, a small smoke pipe and arch brick works of high quality carbon structural steel hot-rolled and cold drawn seamless steel tubes.  High-pressure boiler seamless steel pipe is used for the manufacture of high and above the pressure water tube boiler to heat the surface with high-quality carbon steel, alloy steel and heat-resistant stainless steel seamless pipe.  Seamless steel pipe for high pressure chemical fertilizer equipmentsis is applicable to the operating temperature of -40 ~ 400 ℃, working pressure of 10 ~ 30Ma chemical equipment and pipeline quality carbon structural steel and alloy steel seamless steel pipe.  Petroleum cracking seamless steel pipe is for oil smelter boilers, heat exchangers and their transmission fluid pipe.  Geological drilling steel pipe is the core drilling tubes for geological department,which to be used by end-use can be divided into the drill pipe, drill collars, core pipe, casing and precipitation tubes. Diamond core drill seamless steel pipe is used for diamond core drilling, core rod, seamless steel pipe casing.

Hot Rolling Seamless Steel Pipe Vs. Cold Rolling Seamless Steel Pipe

Seamless steel pipe can be divided into hot rolling seamless steel pipe and cold rolling seamless steel pipe. Next, Prime Steel Pipe will show you the difference between them. Cold rolled seamless steel pipe is a seamless steel pipe for high dimensional accuracy and good surface finish. Cold rolled seamless pipe in addition to include the general steel, low and medium pressure boiler tube, high-pressure boiler tubes, alloy steel pipe, stainless steel pipe and oil cracking tube, also includes carbon thin wall steel pipe, alloy thin wall steel tube, thin-walled stainless steel pipe and special-shaped steel tube. The diameter of cold rolled seamless steel pipe is 6mm, wall thickness is 0.25mm, while the diameter of thin-walled tube can be 5mm, wall thickness can less than 0.25mm. The dimensional accuracy of cold rolling is higher than that of hot rolling. Hot rolling is relative to the cold rolling. Cold rolling carries on rolling below the temperature of recrystallization, and hot rolling is above the recrystallization temperature. Hot rolled seamless steel pipe is generally divided into low, medium, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, oil cracking pipe, geological steel pipe and other steel pipe. The outside diameter of hot rolled seamless tube is generally greater than 32mm and the wall thickness of that is 2.5-75mm.

Tube blank preparation and inspection △→Tube heating→Perforation→Rolling tube→Steel tube reheating→Fixed (reduced) diameter→heat treatment △→finished tube straightening→finishing→inspection △(non-destructive, physicochemical, Taiwan inspection)→Warehousing

PROCESS FLOW CHART OF HOT ROLLED SEAMLESS STEEL PIPE

The main purpose of the perforation process is to become a solid round billet piercing hollow shell. Capillary in the specifications, accuracy and surface quality can not meet the requirements of the finished product, further improvements are needed to deform the metal through. The main purpose of the stretching machine is further reduced sectional view (main compression wall) for a larger axial extension, so that the capillary improved dimensional accuracy, surface quality and organizational performance.

After stretching machine rolled steel pipe shortage collectively need further molding mill in order to achieve the requirements of the finished pipe. Rolled steel due to pass in the method widely used in the production of seamless steel tubes.

So far, due to the method pass rolling steel can be divided into two categories: core pension without rolling rolling (hollow body rolling), and with the mandrel. Sizing machines, reducing mill and stretch reducing mill belonging to the hole without mandrel type continuous rolling mills are generally coffin. Its main purpose is to reduce the diameter of the deformation process or sizing get finished steel, the wall thickness of process control, can make thinning, thickening or nearly unchanged.

All the traditional hole-type rolling machine with mandrel belong to extend machine. The main purpose is to reduce the deformation process perforated capillary wall thickness and outer diameter roll passes in the deformation zone and the mandrel posed, for a larger axial extension. At the same time a certain improvement in the organization, performance, accuracy, surface quality.

Cold drawn seamless steel tubes process:

Round tube → heating → perforation → Heading → annealing → pickling → oiled (copper) → multi-pass cold drawn (cold rolled) → blank tube → heat treatment → straightening →hydrostatic testing (testing) → mark → storage.

PROCESS FLOW CHART OF COLD DRAWN SEAMLESS STEEL PIPE The general cold strip mills, volume should go through continuous annealing (CAPL unit) to eliminate cold hardening and rolling stress, or batch annealing reach the mechanical properties of the corresponding standard specifies. Cold rolled steel surface quality, appearance, dimensional accuracy better than hot-rolled plate, and right-rolled thin product thickness is about 0.18mm, so the majority of users favor. Rolling hard roll can be used as the raw material of the hot-dip galvanizing plant, hot dip galvanizing line set annealing line. Rolling hard roll weight is generally 6 to 13.5 tons, the coil diameter of 610mm.

Heat Treatment of seamless steel pipe

The quality of heat treatment is directly related to subsequent processing quality and eventually affect the performance and life of the parts, heat treatment is the energy consumption of the machinery industry big polluters.

In recent years, with the advancement of science and technology and its application,  heat treatment process for seamless steel pipe is mainly reflected in the following aspects:

(1) Clean the heat treatment Heat treatment production waste water, waste gas, waste salt, dust, noise and electromagnetic radiation and so impact on the environment caused by pollution. Solve the heat treatment of environmental pollution problems, the implementation of clean heat treatment (or the green heat treatment) is one of the developed countries the direction of heat treatment technology development. To reduce SO2, CO, CO2, dust and cinder emissions, has basically put an end to the use of coal as a fuel, heavy oil use fewer, mostly switch to light oil, natural gas is still the best fuel. The The burning furnace waste heat utilization has reached a high degree of, the burner structure optimization and empty – fuel ratio strictly controlled to ensure that under the premise of reasonable burning, reduce to a minimum the NOX and CO; gas carburizing, carbonitriding alternative salt treatment and vacuum heat treatment technology to reduce waste containing salts and CN-toxic water pollution; using water-soluble synthetic quenching oil instead of part of the quenching oil, using biodegradable vegetable oil instead of part of mineral oil to reduce oil pollution.

(2) precision heat treatment Precision heat treatment has two meanings: the one hand, according to the requirements of the use of the parts, materials, structure size, physical metallurgy knowledge and state-of-the-art computer simulation and testing technology, to optimize the process parameters to achieve the desired performance or maximize material Another aspect of the potential; fully guarantee the stability of the optimization process to achieve product quality and degree of dispersion is small (or zero), and the heat distortion zero.

(3) energy-saving heat treatment Scientific production and energy management is the most efficient use of energy has the potential factors, the establishment of a specialized heat treatment plant to ensure full capacity, give full play to the equipment capacity is the choice of the scientific management. Select energy structure in the heat treatment of primary energy; make full use of the waste heat, waste heat; using low-energy, short cycle process instead of a long cycle, energy consumption process.

(4) less non-oxidation heat treatment Heated to precisely control the carbon potential protective atmosphere heating alternative oxidizing atmosphere, controlled atmosphere heated nitrogen potential, to improve the performance of the parts after heat treatment, heat treatment defects such as decarbonization, cracks, greatly reducing the heat after finishing stay reduced , improve the efficiency of material utilization and machining. Vacuum plus hot gas quenching, vacuum or low pressure carburizing, nitriding, carbon permeation and boronizing can significantly improve the quality and reduce distortion, and increased life expectancy.