The category of profile rolled products includes products with a cross-section other than round. These pipes are rectangular, square, hexagonal, oval and others. They have found application in a wide variety of fields, but this type of product is most in demand in engineering and construction. From the steel rectangular pipe GOST 8645 68, car frames, various types of fences, greenhouses, furniture details and other metal structures are made.
The assortment of profile pipes according to GOST 8645-68 includes products of various sizes and sections
Content
Regulatory framework and assortment
The list of regulatory documents for specialized products is quite wide.
- GOST 8645 82, GOST 8645 86, and GOST 8645 68 contain comprehensive information on the type sizes of profile type pipelines and requirements for rectangular steel pipes;
- in GOST 30245 03 you can find regulatory data relating to pipelines of rectangular cross section, as well as having the shape of a square;
- basic information on square sections is present in GOST 8639 82 and GOST 8639 68.
National standards apply to the geometric characteristics of core products - wall thickness, width, and height. In addition, there is another parameter that requires standardization. This is the corner radius.
Important! Their rounding is a necessary measure. If this is not done, then in the corners during torsion deformation stress concentrations will be fixed, the level of which can jeopardize the integrity of the structure.
Pipes longer than 10 cm are the basis for a wide variety of designs
The standard dating back to 1982 applies to the profile products of cold and hot rolled products, as well as to electric-welded products. The size of rectangular steel pipes of the assortment GOST 8645 82 varies in the range of millimeters. And if the products of minimum dimensions are used mainly for the manufacture of railings, then a pipeline with a height exceeding 10 cm can serve as an element of the supporting structure.
The range of GOST 8645 68 rectangular steel pipes contains products with special dimensions. Specific figures are presented in table No. 1.
Table 1
| Wall thickness | Height | Width | Weight is one meter, kg | Cross-sectional area | |||
| millimeters | |||||||
| 8 | 100 | 230 | 38,57 | 49,14 | |||
| 8 | 120 | 200 | 37,32 | 47,54 | |||
| 18 | 170 | 196 | 88,99 | 113,24 | |||
| 12 | 120 | 190 | 51,94 | 66,17 | |||
| 20 | 145 | 180 | 84,10 | 107,13 | |||
| 8 | 130 | 160 | 33,55 | 42,74 | |||
| 7 | 60 | 150 | 20,88 | 26,60 | |||
| 3 | 60 | 140 | 9,02 | 11,48 | |||
| 3 | 50 | 90 | 6,19 | 7,78 | |||
| 7 | 50 | 70 | 10,99 | 14,0 | |||
| 2,50 | 28 | 40 | 2,39 | 3,04 | |||
| 2,0 | 28 | 40 | 1,95 | 2,49 | |||
| 1,5 | 28 | 40 | 1,50 | 1,91 | |||
| 1,5 | 25 | 40 | 1,43 | 1,82 | |||
| 2,50 | 25 | 28 | 1,80 | 2,29 | |||
| 2 | 25 | 28 | 1,49 | 1,89 | |||
| 1,5 | 25 | 28 | 1,15 | 1,46 | |||
Both standard and special pipe sizes are specified by GOST
In addition, the assortment of steel rectangular pipes specified in GOST 8645 86 must meet the same requirements as those contained in the regulatory document from 82 years. The differences are purely cosmetic in nature and relate to compliance with the given geometric parameters.
According to GOST 8645 82, standard sizes remain unchanged. But special sizes can range from 25x28 to 100x230 mm.
Pipe marking
The marking of the pipeline contains comprehensive information not only about the size of the section, but also about the material of manufacture. Depending on the length, there may be such designations:
- GOST 8645 68 / B10 GOST 13663 86;
- GOST 8645 68 / B10 GOST 13663-86;
- GOST 8645 68 / B10 GOST 13663 86;
In any case, the decryption instruction sounds the same. From left to right are indicated: the geometric parameters of the profile and the standard in accordance with the requirements of which the pipe was produced, The length or the multiplicity of the length of the pipeline is also indicated. In the denominator there is a steel grade and the standard to which it corresponds.
In the first example of marking, we are talking about a rectangular pipe GOST 8645 68 with a cross section of 90x40, with a wall thickness of 4 mm and a length multiple of 1.5 meters, steel grade B10.
All the same ˗, only the length is 5.8 meters. The dimensions are the same, the length is unmeasured and steel is B10.
When calculating all the static characteristics, the wall thickness of 1.50 mm is taken as the basis. If serious loads are assumed, taking into account the fact that the value of this parameter can reach 15-18 millimeters, it is recommended to recalculate these characteristics, taking into account the real dimensions of the wall.
The minimum size of square tubes is 10x10 millimeters
A few words about the assortment of square steel pipes GOCT 8645 68. Its difference is determined by the geometry of the cross section of the pipeline formed by walls of the same length. Of course, the sizes compared to rectangular pipes are different: the maximum size is 180 × 180, and the minimum is 10 × 10 millimeters.
On a note! In addition, it is allowed to produce square tube products with special geometric parameters - from 32 × 32 to 65 × 65 millimeters.
Production and tolerances
The manufacture of steel rectangular pipes GOST 8645 86 is carried out in three different ways:
- hot rolled. An all-metal bar acts as a blank here. After heating to a metal recrystallization temperature, it enters the piercing press, where a hollow sleeve is obtained from a monolith. At the calibration stage, the product is given a rectangular shape, and the specified wall thickness and the required diameter are formed on the rollers;
- cold rolled. This technology differs from the previous one in that the workpiece is cooled immediately after receiving the sleeve. Cold forming provides very high precision and increased strength.
- electric welding. Stripes are cut from a steel sheet, which, after welding together, form an endless strip. On the rollers, it is folded into a workpiece with a circular cross section, after which the seam is welded. The desired shape is attached to the round workpiece on the calibration rollers. Checking the quality of the seam is one of the mandatory requirements of GOST 8645 86.
Only those products that comply with GOST standards go to shipment to customers.
It should be noted that other methods of production of such pipe products are not widespread. This point of view was confirmed in the main regulatory documents - in GOST 8645 68 and in GOST 8645 86.
The maximum permissible deviations of geometric parameters are specified in standard 8639, approved in 82 of the past century. The basic requirements are as follows:
- the unevenness of the wall thickness should not lead the pipe parameters beyond the maximum permissible deviations from the standard (nominal) value;
- the deviation of any angle of the pipe from a straight line should not exceed one and a half degrees;
- the curvature per linear meter is not more than 2 millimeters.
Of course, the chemical composition of the metal, although to a lesser extent, also matters. The scope and resistance to aggressive environments depend on it.
Permissible deviations of the main parameters of rectangular steel pipes GOST 8645 82 are presented in table No. 2.
table 2
| Parameter Name | Extreme deviations depending on accuracy | |
| High | Normal | |
| Convexity or concavity of the sides | ||
| For seamless hot formed pipes with side sizes | ||
| More than 100 millimeters | 1.50 mm | 2.0 mm |
| 70.0 to 100.0 mm | 1.20 mm | 1.50 mm |
| Over 50 to 70 millimeters | 0.80 mm | 1.0 mm |
| Up to 50.0 mm | 0,50 | 0,75 |
| For electrically welded and cold-formed seamless pipes with side sizes | ||
| More than 70 millimeters | 0,8 | 1 |
| Over 50 to 70 millimeters | 0,50 | 0,75 |
| Up to 50 millimeters | 0,50 | 0,50 |
| Outside dimensions | ||
| For welded and cold-deformed seamless pipes larger than 50.0 millimeters | ± 0,8 % | ± 0,8 % |
| For products of the same type with sizes from 30.0 to 50.0 mm | ± 0.30 mm | ± 0.40 mm |
| For the same products up to 30.0 mm | ± 0.25 mm | ± 0.30 mm |
| For hot-formed seamless pipes | ± 1,25 % | ± 1,5 % |
| Wall thickness | ||
| For seamless cold-formed and electric-welded pipes | ||
| Wall thickness more than 3.50 mm | ± 10,0 % | ± 12,5 % |
| Wall thickness up to 3.50 mm | ± 12,50% | ± 12,50% |
| For electric welded pipes | ± 10,0 % | ± 10,0 % |
| Twisting rectangular and square pipes | ||
| For cold formed pipes | Two degrees per linear meter as agreed by the manufacturer with the customer | — |
| For hot-formed seamless and electric-welded pipes | — | |
Good to know! Compared to a seam product, a seamless design has advantages only when it comes to internal loads. And external loads of both types of pipes carry equally well.
An important role is played by the composition of steel, which is used for the production of pipes, the quality of finished products depends on the number of components in it
The use of profile and round steel pipes
To find out the scope of a rectangular steel pipe, it is necessary to pay attention to the features that distinguish it from the production of round pipe metal.
- a rectangular pipe GOST 8645 68 and GOST 8645 86 have a much higher bending strength. Moreover, the value of this indicator is the value of the derivative of the direction of the load vector. When it is perpendicular to the axis of the pipe and, accordingly, parallel to its wide side, the strength is maximum;
- any profile pipe made in accordance with the requirements of state standard 8645 86 loses to the pipe round in terms of maximum internal pressure, which will not cause wall deformation;
- with equal specific gravity and the same wall thickness, the cross section of a rectangular pipe will be much smaller than that of a round one. Therefore, its throughput is much lower.
The conclusion suggests itself: a rectangular pipe cannot be used in gas, oil and water pipelines, but only where significant lateral loads are assumed to be present.
The main areas of application of these products include:
- Bearing metal structures. Rectangular pipes GOST 8645 86 are often used as the basis for metal frames of buildings for various purposes. The skeleton of the structure assembled from products of this type is hung with sandwich panels, windows are inserted into the openings, ventilation is organized and air conditioning / heating is established.
- Automotive industry. Due to their strength with the minimum weight of rectangular pipes GOST 8645 82, they become part of the frames of vehicles, including heavy trucks, caravans and even tractors.
- Agriculture. The construction of greenhouses from rectangular pipes has been practiced in this industry for a long time. Industry and private gardeners did not bypass their attention. The trading network sells a solid and lightweight frame in disassembled form. After assembly on the plot, it is covered with a film and that’s it - the greenhouse is ready!
- Furniture industry. Graduates of any educational institution remember their jobs - desks and chairs. Structural strength is provided precisely by profile pipes.
In life, you can meet other situations in which the use of rectangular pipes will be justified. In order to make the right choice of these products, you need to understand the above regulatory documentation and have an idea of the working conditions of the structure.
