Seamless steel pipe is a round, square or rectangular steel with a hollow cross-section and no seams around it. Seamless steel pipe is made from ingots or solid billets by piercing into capillary tubes, and then hot-rolled, cold-rolled or cold-drawn. Seamless steel pipe has a hollow cross-section and is mostly used as a pipeline for transporting fluids. Compared with solid steel such as round steel, steel pipes have the same bending and torsional strength and are lighter in weight. They are economical cross-sectional steels and are widely used in the manufacture of structures. Parts such as oil drilling rods, automobile drive shafts, bicycle frames, steel scaffolding for construction and mechanical parts.
Seamless steel pipe production has a history of nearly 100 years.
The German Manisman brothers first invented the double-slant cut mirror machine in 1885. 1891 invented the cycle rolling machine. 1903 Swiss Stiefel invented the automatic tube rolling machine. Later, there were a variety of active extension machines such as continuous tube rolling machines and top tube rolling machines.And began to develop into a modern enterprise in China. Seamless steel pipe industry.
The 1930s, due to the use of three-roller rolling mill, extrusion machine and ordinary cold rolling mill.The variety and quality of steel pipe has been improved. 1960s, due to the improvement of continuous pipe making machine, the emergence of three-roller perforating machine, especially the enterprise application system tension reducer and the success of continuous casting billet, improve the efficiency of social production management, enhance the ability of seamless steel pipe and welded pipe competition. 1970s In the 1970s, seamless pipe and welded pipe side by side, the world’s steel pipe production at an annual rate of more than 5% growth.
After 1953, China began to attach importance to enterprise development, carried out preliminary research on seamless steel pipe industry, and formed a production management system for rolling various large, medium and small tubes. Generally speaking, copper tubes are also made by ingot beveling, tube rolling machine rolling, steel coil drawing and other processes.
Seamless pipe is a kind of economic section construction steel, which has a very important position in the national economy. It is widely used in petroleum, chemical, boiler, power station, ship, machinery manufacturing, automobile, aviation, aerospace, energy, geology, construction, military, and other industries. etc. in various sectors.
① According to the shape of the section: ring section pipe, shaped section pipe
② According to the material: carbon steel pipe, alloy steel pipe, stainless steel pipe, composite pipe
③ according to the connection method: threaded connection tube, welded tube
④ according to the production method: hot-rolled (extrusion, extrusion, expansion) tube, cold-rolled (pull) tube
⑤ According to the main use: boiler tube, oil well pipe, pipeline pipe, structural pipe, fertilizer pipe…
① Main production processes (main inspection processes) for hot-rolled seamless pipes
Pipe billet preparation and inspection → pipe billet heating → piercing → pipe rolling → pipe scrap reheating → fixing (shrinking) diameter → heat treatment → finished pipe straightening → finishing → inspection (non-destructive, physical and chemical, stage inspection) → storage.
②The main production process of cold-rolled (drawn) seamless pipe
Prepared billet → pickling and lubrication → cold rolling (drawing) → heat treatment → straightening → finishing → the inspection.
Seamless steel pipe is light in weight, its weight is only 1/5 of square steel.
Seamless steel pipe is corrosion-resistant, resistant to acid, alkali, salt, and atmospheric corrosion, high temperature, good impact and fatigue resistance, no need for regular maintenance, the effective service life of 15 years or more.
The tensile strength of seamless steel pipe is more than 8-10 times that of ordinary steel, modulus of elasticity is better than that of steel, excellent creep resistance, corrosion resistance, and impact resistance.
advantages of seamless steel pipe such as excellent mechanical properties and easy processing.
Seamless steel pipe has high elasticity, can be used repeatedly in mechanical equipment, has no memory, no deformation, anti-static.
In recent years, seamless steel tubes have been widely used in various industries. The market demand is too large, and the more enterprises produce seamless steel tubes, the more uneven the quality of products.
The first thing we need to know is that the wall thickness of high-quality seamless steel will be particularly thick, because the thicker the wall thickness of the product, the more economical and practical it is, and if the wall thickness is thinner, the greater the chance of its processing cost. If this happens, the resource cost will be higher. Second, the technology of seamless steel also determines its limitations. General seamless steel has low precision, uneven wall thickness, low brightness inside and outside the tube, high sizing cost, pits, and black spots inside and outside. It is not easy to remove; again, it must be processed offline for inspection and shaping. Therefore, it embodies its superiority in high pressure, high strength, and mechanical structure material. In the process of using it, we will slowly find out.
In fact, seamless steel pipe has entered the market only in recent years. With the increase of market demand, the advantages of seamless steel pipes have been stimulated. However, there are also many counterfeit products in the market. I hope you will be selective in your choice. Must be cautious.
As seamless steel pipe works under high temperature and pressure standards for a long time, the raw material will have stress relaxation, plastic deformation, and ductility reduction, initial mechanism changes, corrosion and other phenomena.
Seamless steel tubes used as heating furnaces should have
Adequate long-term compressive strength.
Sufficient plastic deformation work.
less ageing and thermal ductility.
high oxidation resistance, resistance to fly ash, high temperature gases, steam and intergranular corrosion.
Steel grades of seamless steel pipes include carbon steel and its ferritic, ferritic and martensitic stainless wear-resistant steels. To better improve the thermal efficiency and reduce fuel consumption of thermal diesel generating sets, the trend of large space and high main parameters (high temperature, high pressure) thermal power plant generating sets (above 1000MW) is the dominant trend in all aspects. part of the world. The working pressure of steam is increased to 31.5 to 34.3 MPa, and the temperature of saturated steam is 595 to 650°C. It is moving toward high critical pressure, making higher regulations for seamless steel pipes explicitly. Therefore, the development and design of a new steel grade to consider the use of high major parameters of the power plant boiler. Table 1 shows the commonly used steel grades for seamless steel tubes; Table 2 shows the new steel grades for seamless steel tubes.
In addition, the production and processing of seamless steel pipes vary depending on the steel grade. Take ferritic chrome-molybdenum-vanadium steel as an example. The production and processing of seamless steel pipe are characterized by the following: the finished tube should be peeled, and the amount of peeling is usually 5 mm.
As the steel is too hard, the finished tube needs to be cut or sawed with a co2 laser.
The heating rate should be slower, with a heating temperature of 1120 to 1180°C and a hole-breaking temperature of 1100 to 1160°C; the section of 1000 to 1100°C has excellent plastic deformation and low deformation resistance. So the hole-breaking characteristics are good. The main deformation parameters can be selected according to low carbon steel or carbon steel.
After rolling seamless steel pipe tempering temperature should be 950 ~ 980 ℃, a quenching temperature of 730 ~ 750 ℃, holding time of 2 ~ 3h.
The standard tolerance of seamless steel pipe is relatively strict to ensure professional butt welding. The length of the steel pipe is as long as possible to help reduce the total number of welds.
There are many ways to connect seamless steel pipes, and several common methods are listed as follows.
1. Compression type.
3. Compression type.
4. Push type.
5. Tapered thread type.
6. Socket weld type.
7. Articulated flange connection.
8. Welded type and derivative.
tandem connection combining welding and traditional connection.
Different connection methods are used in different fields due to their different production principles, but in general, they all have one thing in common, namely, easy installation, solidity, and reliability.
Compression type: The pipe is inserted into the orifice of the pipe fitting, fastened with a nut, and the orifice casing is compressed with a spiral force through the sealing ring to play a sealing role and complete the connection of the pipe.
Welding type: The end of the pipe is slotted and the pipe is welded into a ring by hand or automatically.
Flange type: The flange and the pipe are welded by annular argon arc welding and fastened by quick clamps or bolts so that the gasket between the flanges is sealed and the pipe connection is completed.
Press-in type: The pipe is inserted into the pipe fitting, and the pipe wall is pressed into a hexagonal shape with special installation tools, and the inner sealing ring is also changed into a hexagonal shape.
Tapered thread type: The outer thread and the piping are ring argon arc welded, and the inner thread fittings are connected with tapered thread to complete the piping connection.
Seamless steel pipe long-term storage will inevitably have some rusting problems. Once the seamless steel pipe is rusted, it is not good to sell, so how to remedy the rust of seamless steel pipe?
Seamless steel pipe surface is mainly polished with tools such as wire brushes, which can remove loose or warped oxide, rust, weld slag, etc. Rust removal by hand tools can reach Sa2 level, and rust removal by power tools can reach Sa3 level. If there is solid oxide skin attached to the surface of seamless steel pipe, the effect of rust removal by tools is not ideal and cannot reach the depth of anchor pattern required for anti-corrosion construction.
Two methods of chemical and electrolytic pickling are generally used. Pipeline anti-corrosion only uses chemical pickling, which can remove oxide, rust, and old coating. Sometimes it can be used as reprocessing after sandblasting rust removal. Although chemical cleaning can make the surface reach a certain degree of cleanliness and roughness, its anchor pattern is shallow and easy to pollute the environment.
Spray (throwing) descaling is driven by a high-power motor to rotate the spray (throwing) knife at high speed, so that steel sand, steel shot, wire segments, minerals, and other abrasives are sprayed (thrown) on The surface of steel pipe is under the action of centrifugal force. , not only can thoroughly remove rust, oxide, and dirt, but also seamless steel pipe can reach the required uniform roughness under the action of violent impact and friction of abrasives.
Cleaning the surface with solvents and emulsions to remove oil, grease, dust, lubricants, and similar organic substances, but cannot remove rust, oxide, flux, etc. from the surface of seamless steel pipe, so it can only be used As an auxiliary means of anti-corrosion production.