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Shaped steel is widely used in mechanical engineering, the manufacture of metal structures, construction and water supply. The most popular type of structural steel profile is the square. The range of steel square pipes is very wide and diverse. They are much stronger than round ones. It is very important to know the properties of the popular type of rolled steel. In addition, it is necessary to learn how to correctly calculate the weight of the measured segment of the finished product. All this can be found in this article.

## Main characteristics and purpose of a square profile

Square tubes are made in metallurgical plants. Production technology — rolling of convex blanks (GOST 8639-82). Distinctive features:

- great strength;
- high degree of resistance to bending loads.

The main material for manufacturing is carbon (GOST 9045, 380, 1050) and low-alloyed (GOST 19281 — 10KhSND, 09G2S; GOST 4543 — 30KhGSA, 10G2) steel grades. Various chemical elements are used as alloying additives. The standards contain requirements for square finished products:

- chemical composition;
- appearance;
- manufacturing accuracy class;
- limit loads.

For a square, it is critically important to observe the principle of uniformity in the distribution of loads over the section of the workpiece. Its strength characteristics, despite the hollow internal structure, are much higher than those of other types of rolled products. A square profile is stronger than others, since it has a high radius of gyration around the perimeter, as well as a cross-sectional area of the finished product.

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The main physical indicator that reflects the ratio of flexural rigidity to that of compression is the radius of gyration of a square profile. The most economical profiles with equal to each other the smallest / largest radii of gyration. The equality of the central moments of inertia is a guarantee of an excellent strength indicator.

An important physical characteristic of an equilateral profile is the moment of resistance. Its correct calculation will help to avoid errors during the installation of the structure. For wide wall pipes, the moment of inertia is the difference between the fourth power of the outer/inner wall length divided by six outer wall lengths. The moment of resistance of a thin-walled pipe is the square of the outer length multiplied by 4/3 of its thickness.

## Product range

Equilateral in length / width steel profile is of three types:

1) Cold-formed seamless.

Products made in this way from carbon steel are not of high quality. The most attractive characteristic of such products is their low cost. The range includes 17 standard sizes. The size of the side can vary from 10 to 120 mm. Each of the standard sizes can have a different wall thickness — from 1 to 8 mm.

2) Hot-formed seamless.

The temperature deformation method is used to obtain finished products with standard sizes from 30 to 160 mm. The crystal structure of the metal does not change during heating, and the quality is much higher than during cold deformation. The walls can have a thickness of 4 to 14 mm.

3) Electrowelded.

Equilateral profile pipe with a straight weld, manufactured using high-frequency automatic electric welding, has 15 standard sizes. The wall thickness ranges from 1 to 5 mm. The profile can have a side section from 10 to 100 mm.

For the needs of customers, cutting of finished products is carried out into two types:

- random length — from 4.0 m to 12.5 m (hot-formed seamless), from 1.5 m to 9.0 m (cold-formed seamless and electric welded);
- measured length — from 4.0 m to 12.5 m (hot-deformed seamless), from 4.5 m to 11.0 m (cold-deformed seamless), from 5.0 m to 9.0 m (electro-welded).

All of the above indicators of the lengths of measured / non-dimensional segments are strictly regulated by the requirements of the standard.

According to GOST 19903-2015, finished products of equilateral section may have the following maximum deviations:

- for a profile with a width of less than 100 mm — ± 1.0, but not less than ± 0.5 mm.
- for a profile with a width of more than 100 mm — ± 0.8 mm.

Permissions also apply:

- to the radius of the outer rounding t;
- for deviation from right angle 90
^{about}.

## Scope of application of square pipes

The vast majority of rolled steel with equal edges is used in construction. It is used in the construction of frame metal structures of various types:

- gazebos;
- visors;
- canopies;
- gate;
- fences;
- greenhouses;
- flyovers.

Due to the equal sides, the measured segments are very conveniently connected to each other. When fastening, coupling or bolted connections can be used. In addition, a hollow square with equal faces can be used as a reinforced formwork fastening for concrete mass solidification.

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In industry, various frame structures are made from a steel square. For example, from segments of a small section, they are used for mounting the frames of tent trucks. With the advent of a large number of different types of fittings, the square has become widely used in the manufacture of furniture. In this case, the profile undergoes additional processing:

- chrome plating;
- galvanizing;
- applying a polymer coating.

## How to calculate the weight of a linear meter of a square profile pipe

The most important role for compliance with the parameters of structural strength is played by the correct calculation of the weight of rolled metal. It is needed in order to plan expenses. If rolled products are sold in running meters, then in the mathematical calculations of strength, only the weight characteristic in kilograms or tons is used. Depending on the estimated weight of the profile, you can easily determine the most convenient way to transport it.

There are three ways to calculate the weight of a metal profile:

- Tabular.
- Formula.
- Computer.

All calculation methods are based on a constant finished steel density of 7850 kg/m^{3}. The tabular calculation is based on calculations previously made and included in GOST calculations using constant values. In fact, data on the dimensions of the workpiece, wall thickness and radius of curvature of the corners may differ for each individual sample. Therefore, this method is considered theoretical, and does not allow obtaining information about the exact weight of the measured segment.

For the convenience of calculating the weight of a metal structure, an online calculator is used. This is a special program for the implementation of engineering calculations. Finding it online is very easy. She usually takes into account all the nuances. To get started, three main parameters of the measured segment of the finished product are required:

- Length;
- Height Width);
- wall thickness.

The program independently calculates three indicators:

- radius of inertia;
- moment of inertia;
- moment of resistance.

The task of the calculation is to establish the weight of a segment of a square of a given length.

The most accurate from a mathematical point of view is the formula calculation. The weight of 1 meter square pipe is:

m = 2*h*(A+B)*q

In this formula

m is the mass of one meter, kg.

h is the profile wall thickness, m.

A and B are height and width values equal to each other, m.

q – steel density value, kg/m^{3}.

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As a rule, the result of the formula calculation differs from the data indicated in the table. This is because the formula does not include curvature radii inside/outside the measured segment. There is no steel profile with perfectly right angles. More precisely, they take into account all the nuances of shape and size when calculating the weight of 1 meter of the GOST table. It is very important to choose the right online calculator.

## Advantages and disadvantages of square steel profile

Metal structures, which are mounted using finished square-section products made of low-alloy steels, are characterized by the following operational qualities:

- mechanical strength.
- durability.
- high corrosion resistance.
- small material consumption.
- ease of processing and installation.

A large assortment of products manufactured in accordance with GOST 8639-82 allows you to select the necessary measured lengths for the installation of the most complex structures. The square has very good resistance to bending and twisting. Square pipes are used in various conditions.

The disadvantage of finished products is the high susceptibility to corrosion of pipes made from unalloyed steel grades by cold deformation. Oxygen has a negative effect on equilateral steel pipes. To resist corrosion, they must be subjected to additional processing.

The use of a square profile greatly facilitates the production process. Assembly of frame structures is much faster. The strength of such compounds is at a very high level due to advanced manufacturing methods and subsequent thermal and thermochemical processing.

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