In various areas of production (industry, energy, construction, fabrication of metal structures, water disposal), profiled steel pipes are used. A considerable share in the total volume of semi-finished products is a rectangular pipe. The range of steel products produced by metallurgical plants is extremely wide. It is very important to be able to correctly select the type, profile range for specific conditions for the manufacture of a structure, to be able to quickly and correctly calculate its weight and dimensions.
Main characteristics and purpose
A profile pipe is a hollow metal product with various sections. There are two main methods for manufacturing such pipes:
- cold or hot drawing (rolling);
- electric welding.
One of the most popular sections is a rectangle. It is much more complicated than a circle in terms of geometry and processing methods. But a rectangular pipe, in comparison with a round counterpart, has a noticeable advantage. A structure made of such pipes has higher bending stiffness characteristics. This allows it to handle high lateral loads very well.
Rectangular steel profiles are manufactured in accordance with the requirements of GOST 8645-68 “Steel rectangular pipes. Assortment». Pipe dimensions must comply with the requirements of this document.
Steel composition, physical and mechanical properties define standards related to manufacturing methods:
- GOST 10704-91 «Steel electric-welded longitudinal pipes».
- GOST 10707-80 «… cold-formed electric-welded steel».
- GOST 9941-81 «… seamless cold- and heat-deformed from corrosion-resistant steel.»
For pipes used in construction, another GOST has been adopted — 30245-2003. It differs from the primary standard in a wider choice of geometric dimensions. So, the maximum section of the profile for use in industrial / civil construction is 400×200 mm. The standard spells out all the basic requirements for the manufacture, labeling, packaging, transportation of semi-finished products, the rules for acceptance, storage and quality control.
Electrowelded products are made from steel strips (strips) of various thicknesses by winding on a drum and rolling. The pipe billet is connected using various welding methods (arc, induction, laser, plasma). The final stage in the manufacture of a profile with right angles is the calibration of the form. The quality of the welded seam in accordance with the requirements of GOST is checked by the flaw detection method.
Product range. Pipe weight calculation
The requirements of the 8645 standard determine that a steel rectangular pipe can have dimensions from 15×10 mm to 230×100 mm. The minimum cross-sectional area — for a pipe 15×10 with a wall thickness of 1 mm — 0.443 cm2. Oddly enough, pipes of not the largest size have the highest indicator in diameter:
- 196×170 mm — 113.24 cm2;
- 180×145 mm — 107.13 cm2.
This is due to the very large thickness of their walls — 18 and 20 mm, respectively.
The standard defines the limit values for deviations of external dimensions for products manufactured in accordance with different accuracy classes:
- Increased — hot-rolled — ± 1.25%; cold-rolled and welded — up to 30 mm — ± 0.25 mm, 30-50 mm — ± 0.3 mm, over 50 mm — ± 0.8%.
- Normal — hot rolled — ± 1.50%; cold-rolled and welded — up to 30 mm — ± 0.30 mm, 30-50 mm — ± 0.40 mm, over 50 mm — ± 0.8%.
Semi-finished products are also certified for moment of inertia, degree of concavity and convexity. In addition, the deviation of the wall thickness of electric welded products cannot be more than 10%. For products obtained by cold or hot deformation, the same figure is 12.5%. Maximum twisting — no more than 2 degrees, curvature — no more than 2 mm per linear meter of length. According to GOST, the moment of resistance and the mass of one running meter of semi-finished products of various sections and wall thicknesses are also strictly controlled.
The determination of the weight of profile products with the presence of right angles is carried out for the subsequent mandatory calculation of the structural strength. The weight of one linear meter of a rectangular metal pipe is calculated by the formula:
m = ro / 7850 * 0.0157 * S * (P — 2.86 * S) * L,
where 7850 kg/m³ is the steel density. In addition, for the calculation, data on the pipe section (a and b), wall thickness S are required. The length of the product L in the default formula is 1 m. This indicator is changed if it is necessary to know the weight of the cut-to-length profile section. For the convenience of working with mathematical values, GOST includes a table of weights for 1 m of a rectangular profile pipe.
Rolled products with right angles are considered thin-walled if the ratio of the outer diameter to the wall thickness does not exceed 0.025. A rectangular profile with a ratio of 0.5 is considered standard, thick-walled — +0.1.
High-quality semi-finished products are made with rounded corners. The optimal radius is a value equivalent to twice the wall thickness of the product. Practical application in the industrial production of semi-finished products has received an overestimation of the radius. This process has two goals:
- Lighten the design.
- Reduce the cost of installation work.
Despite the external beauty and elegance, semi-finished structures with the lowest rounding angles are much heavier than standard options. From the point of view of mechanics, a search for a golden mean is required: the bearing characteristics of a metal structure are reduced by the use of pipes with both large and ultra-small angular curvature.
Scope of rectangular pipes
A wide range of semi-finished products with a right angle has significantly increased the list of industrial production areas in which they are successfully used:
- Manufacturing of frame structures.
By varying the cross section of the walls, the dimensions of the measured segment, it is possible to significantly increase the degree of strength of the structures being erected. The rectangle is very popular in the construction of long-span structures — warehouses, hypermarkets, hangars, greenhouses, greenhouses, sports complexes.
- Arrangement of railings and fences.
The ease of installation of stainless steel products makes them popular for decorative purposes. Due to its excellent anti-corrosion properties, the rectangular pipe can be used outdoors for several decades.
Recently, rectangular steel pipe elements have become widespread in relatively new industries:
- Installation of automotive structures.
Light weight and excellent mechanical properties allow the use of steel semi-finished products of various sizes with right angles in the automotive industry.
- Manufacture of metal frame furniture.
From a thin-walled rectangle, metal parts of various pieces of furniture for schools and universities are mounted in large quantities — tables, chairs, desks, shelves.
The main material for the manufacture of such structural elements are AiSi304 and AiSi316 stainless steels. They are characterized by high temperature resistance, slightly subject to abrasion and corrosion. A big plus is the availability of several different finishes for finished steel structures.
Advantages and disadvantages of rectangular steel profile
There are some features of the marking of finished products depending on their mechanical properties. For profiles in the nomenclature of which the letter A is present, only mechanical properties are regulated. If the letter B is present in the marking, strict observance of both mechanical and chemical properties is necessary. Rectangular profiles are also tested for impact strength after the artificial aging of steel. The presence of the letter D in the marking indicates that the semi-finished products have passed hydraulic tests.
Marking of rectangular semi-finished products must comply with the requirements of GOST 7566-94, contain the following information:
- manufacturer information;
- designation and length of the profile;
- melt number;
- OTC mark.
Pipes with right angles cannot be used in the manufacture of plumbing communications. There is a clear scientific explanation for this: due to the smaller internal volume, a significantly smaller amount of liquid is pumped through a linear meter of a rectangular pipeline than when using a round segment. In addition, shaped stainless pipes are not able to withstand significant internal loads. Therefore, the scope of round and square profiles is clearly delineated.
A comparison of a steel bar of the same section shows that its weight is much greater than that of a hollow dimensional segment with right angles. Consequently, structures assembled from a hollow rectangular pipe have a significantly lower total mass and greater efficiency with comparable strength indicators. The process of mechanical processing of a rectangular profile does not present any particular difficulties. Its cutting takes much less time than the division into parts of a solid profile (rod).