Pipes made of steel seamless hot-deformed can produce more reliable and stronger than pipelines from welded products. These products are widely used for the manufacture of machine parts, structures and other technical purposes.
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Pipes seamless hot-deformed, GOST 8731-74 for which regulates the technical requirements for quality, are made of carbon and alloyed steel grades. For the production of these pipes, forged, continuously cast and rolled billets are used which are preheated in a special furnace to a temperature exceeding 50 ° C for recrystallization of steel.The exact thermal parameters depend on the grade of the alloy. The metal of the billet acquires plasticity sufficient for the forthcoming processing.
Depending on the assortment of pipes required for their quality requirements, as well as the physico-chemical characteristics of the starting material, hot deformation is produced in various ways, the technological scheme of each of which includes the following sequence of common elements:
- after heating the metal, a sleeve (hollow preform) is obtained;
- the sleeve is rolled out - a black tube is obtained;
- reduction and calibration - the final formation of the diameter and wall of the pipe.
If necessary, preheating of the pipe can be carried out before each subsequent technological operation.
The liner is produced by one of the following methods:
- on the press;
- in mills for screw rolling;
- a combination of the previous processes (combined): the production of a thick-walled glass with a press roller shaking or pressing with subsequent flashing of the formed bottom and rolling the wall of the received sleeve in the elongator mill (equipment for screw rolling).
Methods for producing a rough tube:
- on a pilgrim periodic pellet rolling mill;
- in a continuous rolling mill;
- helical rolling on roller mills (mainly in 3-hvalovom Assel, less often - in 2-dvuskovom Dyshera or Accu-Roll);
- on the rack mill - the sleeve is pushed through calibers, which decrease in diameter and have roller holders;
- extrusion of metal on a tube press into an annular gap.
The final size of hot-deformed tubular products is usually obtained in reduction or calibration mills of continuous longitudinal rolling, much less often - on screw rolling equipment. In aggregates with a tandem (automatic mill) mill and a rack mill of the above technological operation, it is preceded by a ringing (rolling in the equipment for screw rolling). In some pipe-rolling units, which are specially designed for the production of seamless pipe products of large diameters, in the final operations it is possible to use expansion mills.
The finished rolling cools down, after which it is cut into standard pieces. As a result, the manufactured product must meet the requirements of the state standard - a hot-deformed pipe GOST 8732-78, which lists the range for this type of metal.
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According to the assortment, these pipes are manufactured in length by the following lengths:
- unlimited length - in the range of 4-12.5 m;
- products of dimensional length - segments within the dimensionless;
- production in the length of a multiple dimensional - segments within the bounds of an immense one with an allowance of 5 mm for each cut;
- products of approximate length - lengths within the immeasurable.
The outer diameter of the pipes produced is in the range of 20-550 mm, the wall thickness is 2.5-75 mm. An important characteristic is the ratio of the product diameter to the thickness of its wall. According to this indicator, experts classify pipe products for:
- thin-walled - the coefficient varies in the range of 12.5-40;
- thick-walled - ratio above 6 and up to 12.5;
- reinforced (especially thick-walled) - the coefficient is 6 or less.
When making pipes, they cut their ends at a right angle, but in the process of cutting, the chamfer can be formed, which has an angle of at least 70 ° to the product axis. Cutting products with a wall thickness of 20 mm and higher can be made by saw, autogen or plasma equipment. In the last two cases, the allowance for the length of the product must be at least 20 mm for each cut. At the ends of pipes with a wall of 5-20 mm to be welded, at the request of the user, chamfers are cut at an angle to the end of the product at 35-40 °. In this case, leave the end ring, in which the width should be 1-3 mm.
Advantages of seamless hot-formed pipes:
- durability and high reliability due to seamless manufacturing technology;
- excellent resistance to temperature changes;
- production of alloy steels is less susceptible to corrosion processes.
The main disadvantage of using these pipe products is the appearance of corrosion, the spread and impact of which can be partially reduced by various methods (for example, using anti-corrosion or other special coatings). In addition, deposits of substances, materials that form part of the liquid transported through the pipe, may form on the inner surface, which leads to a reduction in the conditional passage of the product. These pipelines must be carefully insulated, as the steel has a high thermal conductivity. It is especially important to do this in case of a street laying to prevent large energy losses of the coolant.
Advantages of thick-walled products:
- increased strength and durability;
- a small index of linear temperature expansion;
- the opportunity to choose products with thick walls.
If we compare hot-deformed pipes with seamless products produced by the method of cold deformation, they are more brittle, but less susceptible to corrosion.
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The technology of joining seamless pipes coincides with the methods of joining welded products. However, the difference in diameter and wall thickness determines a number of features. From these parameters depends on the choice of the optimal method for obtaining a hermetic connection of pipeline elements from seamless products.
Threaded mating can be used for systems of small diameter with walls of normal thickness or thin. Cutting is performed on a lathe or with dies. For thin-walled products, this technique is not always appropriate, since the manufacture of threads of the required depth in some cases can lead to a violation of the integrity or strength of the structure. The rest of the cutting process is facilitated by the absence of a seam.
Pipeline systems are presented with a number of requirements, among which the priority is to ensure high reliability and durability. Most often, the choice stops on hot-deformed seamless pipes, which are able to demonstrate these characteristics throughout the life of their operation. These designs are characterized by high technical characteristics, which is due to the use for their manufacture of a special technology that meets the requirements of the state standard. Thanks to this, pipes of this design successfully cope with the task assigned to them and in difficult operating conditions.
Production of seamless hot-deforming pipes
As a raw material, a rod-billet having a circular cross-section is used which is placed in an oven heated to a high temperature. As steel is processed, the steel acquires a plastic structure, which makes it possible to perform the necessary manipulations with it. According to GOST, the technology of making a full cylinder requires the use of special piercing mill, through which the bar is passed. After this, the heated workpiece is given the required geometric dimensions by crimping and drawing, for which a large number of rollers are used.
Inside the workpiece, a mandrel is retained, due to which the inner surface of the pipe does not lose its original geometric dimensions. The metalworking process is completed by performing an operation such as calibration, followed by cooling the workpiece and cutting it into fragments of the required length. The technology for manufacturing a cold, deformed seamless steel pipe is, for the most part, similar to the manufacturing process of the above method: before the roll is started to be processed, the workpiece is first cooled, and after the rolling, it undergoes additional heat treatment.
Pros and Cons of Seamless Steel Pipes
Considering the merits, which provides the technology of manufacturing of these products, it is necessary to mention the following:
At the same time, against the background of hot-deformed seamless steel pipes, the products made by the method of cold deformation exceed the first in strength and resistance to corrosion processes.
Scope of application
Seamless metal pipes can be used in a variety of areas, which depends primarily on their qualities. This should include excellent tensile strength, no seam, no leakage and the possibility of creating products that have particularly thick walls. Noteworthy is the fact that wall thickness 75 mm is not the maximum limit, if it is a question of standard hot-deformed materials. A variant is possible when these designs have non-standard dimensions with respect to their wall thickness. For the manufacture of such pipes, the method of longitudinal drilling of a blank is resorted to. A distinctive feature of such products is the high price.
The widest representation of seamless pipes was obtained in power engineering, in the construction of hydraulic systems, oil production, shipbuilding and aviation, as well as in the chemical and automotive industries.
Hydraulic cylinders The traditional designs are in the form of pistons, the shell of which contains oil, supplied under high pressure, which causes the material to come out. The most common material for the piston is stainless steel, and the product itself is necessarily polished. The use of black steel is impractical because of its rapid coverage with rust, which is due to the interaction of the structure with atmospheric air. If we talk about the hydraulic cylinder itself, it has the execution of a conventional seamless thick-walled pipe.
In power engineering, where seamless pipes are very common, one of the key parameters is thickness of these structures. In this area, heat production is not the only task. In addition, it is necessary to adjust the operation of the system so that the boiler gives it to heat the water in the heating main or to rotate the turbine. The boiler contains such vulnerable parts as screens and screens, which, under the constant influence of a very hot steam, can burst.
All this allows us to say that it depends on the thickness that the material can effectively deal with the stress on the gap, and also how long it will last until it is completely burnt. If there is a need to open a boiler for repair work, it is necessary to face serious difficulties, both financial and physical. In addition to the fact that you have to spend big expenses on repairing, it's no less expensive and the heat supply is cut off. For this reason, the choice in favor of seamless, thick-walled pipes makes it possible to reduce costs to a minimum.
In the field of oil production, the main activities consist of drilling wells, installing casing, pumping out black gold and delivering it with the help of an oil pipeline. Most often standard depth of wells starts from 100 meters, the drill used can cope with the rocks of any structure, and the casing used must effectively resist the movement of the soil. In addition, tubing must be able to cope with increased pressure.
It is quite logical that the chemical industry was spread along with thick-walled and thin-walled pipes. What are they used for? There are situations when during the polymerization of gases or the processing of oil there is a need for high pressure. And here laboratories have to deal with highly toxic drugs. Of course, such pipes need not have special tensile strength, however, in the case of leakage of even a few molecules, this can lead to serious problems.
In such situations, seamless metal pipes come to the rescue: the absence of seams implies that there will be no leakage during operation. High-demand thin-walled pipes are used in automobiles, shipbuilding and aviation. This is due to the advantages that are characteristic of these products, such as minimum weight and strength. And the choice in their favor is quite logical, given that with a small weight will not have to spend more fuel.
Thus, seamless metal pipes are used in many industries:
Product classification
According to GOST, all metal hot-deformed seamless pipes can be divided on the basis of such a feature as the ratio of the thickness of the walls and the outer diameter.
In view of the fact that in the range of products under consideration, wall thickness in the range from 2.5 to 75 mm and an outer diameter of 20 to 550 mm, they can all be classified into the following types:
- Thin-walled, for which the coefficient can be from 12.5 to 40.
- Thick-walled, for which the coefficient can be from 6 to 12.5.
- Particularly thick-walled, for which a ratio of up to 6 inclusive is characteristic.
Also, according to GOST, there is a classification based on such a feature as the purpose and features of the technology used for manufacturing. In accordance with it, these pipes are of round and square section. For pipe blanks, a separation into cast, rolled and forged. For production purposes, they are supplied in the form of rods, as well as continuously cast preforms or ingots.
In addition to this number of key factors, the accuracy of the geometry of the wall thickness and the outer diameter of the pipe should be included. Important for the manufacturer are and quality indicators, fixed by the requirements of the state standard for the standardization of the chemical composition of steel and the mechanical properties of rolled metal.
Requirements of GOST 8732 78
If we proceed from the current requirements, then for hot-deformed seamless steel pipes, there is a division into a dimensional and non-dimensional length. At the standard level, possible deviations along the length of the product are also fixed: up to 15 mm for a length exceeding 6 meters or minimum diameter of 152 mm. In some cases, a slight deviation in the wall thickness is not a violation, but here everything depends on the specific diameter of the pipe and the quality category.
Pipes, steel, hot-deformed seamless boiler-houses
When manufacturing products designed for operation in conditions of supercritical temperature and pressure, manufacturers should focus not on GOST, but on specially designed technical specifications TU 14-3-460-75.
These structures are widely used in the construction of pipelines for steam boilers. The raw material for their manufacture is usually alloyed and carbon steel.
Profile hot-formed seamless pipes
According to GOST, the technology of manufacturing of seamless seamless tubes of hot deformation of rectangular or square cross section provides for the use of special equipment necessary for performing such operations as pressing and compression in workpiece rolls having a circular cross-section. The vast majority of such products are used in the engineering industry and in various areas of the construction sector.
According to GOST, for seamless profile metal products restrictions, which consist in the prohibition of their use for the delivery of liquid media.
Seamless hot-formed steel pipes are available for sale at different prices, which are determined by their external and internal parameters, quality level and other technical properties. These designs represent the category of expensive rolled products against the background of similar welded products, which is due to the peculiarities of the technological process.
For this reason, most often they are resorted to in the arrangement of plots, which are highly demanded in terms of reliability. First of all, we are talking about the construction of highways chemical and oil and gas processing industry, where the most demanded thick-walled pipes. In accordance with GOST, the main sphere of thin-walled products application is the construction of trails in the housing and communal services sector.
How is seamless pipes made?
Solving the problem with the preferred method of joining products, the main attention should be given to such a parameter as the thickness of the walls. According to GOST, if the structures have very thin walls, then this requires great accuracy when performing assembly work. If you have to deal with products that do not have threaded threads, then they are connected using the gas welding method.
According to GOST, the use of electric welding is possible only if the specialist has sufficient skills, knowledge and practical experience in performing such work. But it should be remembered that it is enough to make a small mistake, and the expensive construction will already be unsuitable for use.
In accordance with GOST, for threaded products it is permissible to perform cutting using a lathe or manual method. Carrying out similar works, you do not have to worry about that you can damage the seam. Such a risk is excluded, because these products do not have a welded seam. Except here are only pipes characterized by the presence of very thin walls. The use of such a method increases the risk of cutting them through.
According to GOST, the joining of structures with thick walls can be started by welding only after the chamfering is completed. Neglect of this advice can lead to the fact that the product will lose its former strength. The welding work itself should be carried out using at least 4 electrodes. To resort to the help of a gas burner is considered unacceptable, since it has weak efficiency.
Assortment
The range and standards of the products in question are among the important factors that must be taken into account when choosing these products. All of them can be classified into the following groups:
Conclusion
Hot-deformed seamless pipes have been widely used in various fields, primarily construction and industry
One type of steel seamless pipe is. It is so called because it is obtained by the method of deformation of the preform heated to a high temperature. This can be hot rolling or hot pressing.
Hot-rolled pipes is produced on special pipe mills. The general scheme of their production consists of two basic operations:
1. Operation firmware. Here we obtain a thick-walled sleeve from a special continuous blank;
2. Obtaining a pipe from a thick-walled sleeve. Here hot tubes rolled to the right size.
The first operation is performed on piercing mills, and the second is performed on rolling mills of various designs. In addition to the basic operations, additional finishing is also performed. With their help hot tubes more precise dimensions and cleaner surfaces are obtained. Sometimes they are required to reduce the diameter and thickness of the wall.
Pipe seamless hot-deformed The following types are produced: general purpose, corrosion-resistant and special.
Hot-deformed pipes of general purpose
Hot-deformed pipes (abbreviated as DG) of general purpose are issued on the basis of. The technical requirements for these pipes are determined.
GOST 8732-78 regulates the size of the outer diameter, wall thickness and accuracy of these dimensions.
Hot-rolled pipesis produced with an outer diameter of 45 to 550 mm and with a wall thickness of 4 to 75 mm. The length of such pipes can be from 4 meters to 12.5 meters.
Pipe made of steelGOST 8732-78 is supplied in length, which is specified in the order.
Pipe seamlessGOST 8732-78, depending on the quality index is issued the following groups:
- Group A - with the normalization of mechanical properties. This group is made of steels of st2cn, st4cn, st5sp, st6sp;
- Group B - with the normalization of the chemical composition from the calm grades of steel to, and;
- Group B - with the normalization of mechanical properties and chemical composition of steels of grades according to GOST 1050-88, GOST 4543-71 and GOST 19281-89;
- Group G - with the normalization of mechanical properties of steels of GOST 1050-88, GOST 4543-71 and GOST 19281-89. The control is carried out on heat-treated samples;
- Group D - without the normalization of mechanical properties and chemical composition, but with a hydraulic pressure test.
All hot-deformed pipes, which are designed for operation under pressure, are subjected to a hydraulic pressure test. They must withstand the pressure up to 29 MPa (200 atm.) Inclusive. Besides seamless pipeGOST 8732-78 passes bending tests in accordance with GOST 3728-78. Pipe st 09G2Sfully retains its strength even in severe frost. Therefore, such a dG pipe It is supplied in the region of the Arctic north.
Pipe made of steelGOST 8732-78 takes a big share in the markets of pipes sold. Used seamless hot-deformed pipe for the laying of pipelines carrying a large load and having a large internal pressure in the pipe itself. These are the main oil and gas pipelines and their outlets, city gas pipelines, gas and oil supply pipelines in the fields with a diameter of up to 530 mm.
Besides, dG pipe It is used in mechanical engineering, shipbuilding, power engineering as blanks for manufacturing various parts and assemblies. Of these, hydraulic and pneumatic cylinders, rings, high-pressure cylinders and other similar parts are made.
Hot-formed corrosion-resistant steel pipe
Hot-deformed pipes from corrosion-resistant steels is manufactured according to. This document determines the size, range, accuracy and technical requirements for hot tubes from corrosion-resistant steels. This standard provides for a wide range of pipes with diameters from 57 to 325 mm and with walls from 1.5 to 28 mm thick. The length of the pipes is from 1.5 meters to 10 meters.
As a material for this type of pipe, steel grades with chemical composition are provided. They are such brands as: 08Х13, 12Х17, 12Х18Н10, 10Х23Н18, 12Х18Н9Т.
GOST 9940-81 provides that the pipes must have certain mechanical properties for each steel grade.
Finished hot rolled pipe selectively subjected to tests for mechanical properties, flattening according to GOST 8695-89. In addition, the pipes are tested by hydraulic pressure in accordance with GOST 3845-75.
Main areas where applicable seamless hot-rolled pipes from corrosion-resistant steels are pipelines for aggressive media, and also working at high temperatures. These are pipelines of chemical enterprises of oil refineries, nuclear power plants. In addition, they are used as blanks for the manufacture of various vessels and parts of metal structures that operate at high temperatures and in corrosive environments.
Hot-deformed steel special steel pipe
This type of pipe includes the following varieties:
- Pipes for oil refining and petrochemical industry;
- Precision steel pipes;
- Pipes - blanks for machining.
Hot-deformed steel pipe for oil refining and petrochemical industries are produced by.
According to this standard, the pipes are produced in two groups:
- Group A - the pipes are manufactured completely according to GOST 550-75;
- Group B - pipes for the assortment and dimensions are in accordance with GOST 8732-78, and the technical requirements are fulfilled in accordance with GOST 550-75.
Pipes of Group A are available in diameters from 20 to 219 mm, where the walls can be 2 to 25 mm thick. By length, pipes from 4 to 12.5 meters in length can be ordered. Pipes of group B in accordance with GOST 550-75 are produced from steels of grades 10, 20, 09Г2С, 10Г2, 12ХМ, 15Х5М, 12Х8ВФ, 12Х8, 1Х2М. Pipe st 09G2Sone of the representatives of such pipes.
These pipes are subjected to strict control. From the batch of pipes, samples are taken and subjected to testing for mechanical properties, microstructure of the metal and hydraulic pressure. All these tests are conducted on the basis of relevant standards. These pipes are used in oil refineries in boilers and pipelines, with high vapor pressure and in the petrochemical industry for cracking petroleum products.
GD Pipe steel precision produced on the basis. This is a pipe of increased accuracy. That is, its wall thickness and outer diameter are more precise than steel pipeGOST 8732-78. The outer diameter of these pipes is 25 to 325 mm, and the walls are 3 to 45 mm thick. The length of the pipes is from 1.5 to 11 meters. This pipe is used as a blank for the manufacture of hydraulic and pneumatic cylinders, pistons, rings and other parts working under pressure in various mechanisms and machines.
Pipes - blanks for machining are produced by. This document determines the size, range and accuracy of manufacturing of these pipes. The outer diameter of such pipes varies from 42 mm to 325 mm. Wall thicknesses from 3 to 40 mm. The length of the pipe can be from 1.5 meters to 11.5 meters. Limit deviations in the wall thickness, the outer diameter and the length of the pipe are set exactly the same as seamless pipeGOST 8732-78.
Hot-deformed steel pipe - the blank for machining is made of steels of grades: 10, 20, 35, 45, 30ХГСА, 30ХМА, 09Г2С, 10Г2, 15Х, 40Х, 15ХМ, 38Х2МЮА. An example of such a pipe can be pipe ст 09Г2С. The finished pipes are checked for compliance with the claimed chemical composition, mechanical properties, and microstructure of the metal. Hot-rolled pipes should be checked for hidden defects by non-destructive inspection methods.
As the name suggests, such pipes are used as blanks for manufacturing parts on metal cutting machines and stamping presses. Of them, such details as: glasses, cylinders, rings, nozzles, branch pipes are made. The use of pipes helps to reduce the time for machining in the manufacture of parts and reduce the consumption of metal. And this leads to a reduction in the cost of production.
To order seamless hot-deformed.