- What is a profile pipe
- How are shaped pipes made?
- Technological advantages of shaped pipes
- How to choose a profile pipe
- Mode of production
- Manufacturing material
- Rounding corners
- Wall thickness
- Special mechanical properties
In this article, we will talk about shaped steel pipes as a versatile building material. It will focus on the various uses and their unique properties. Let’s talk separately about what criteria should be used to choose square and rectangular pipes.
Despite successive crises, suburban construction continues to develop, more and more of our compatriots want to have their own home away from noisy megacities. Wood, concrete and brick are traditional materials for the construction of buildings, but it is never complete without metal rolling, since all monoliths need reinforcement, profiles for frames, beams for floors, nets and profiled sheets are needed.
Thanks to welding, it is possible to create products of any shape from metal, while the joints have a strength not lower than the steel mass. In addition, metal parts can be bent and deformed by pressure, forged under heating. Any metal structures will always be lighter and more compact than elements of stone and reinforced concrete similar in function. With proper assembly and proper care, they are much more durable, especially if you choose a specific metal or steel grade that provides the workpiece with performance characteristics suitable for certain conditions..
If we talk about complex spatial metal structures for the yard, then there is no equal to metal at all, because it compares favorably with its plasticity and high bearing capacity. Gazebos, stairs, awnings, fences, gates, benches, all kinds of frames – the list is endless. Most often, for these purposes, a rod is used to create forged products and shaped pipes as an element of the supporting system. In our country, profile metal products began to be actively used not so long ago, but the popularity of square and rectangular pipes is growing steadily. They are getting better and cheaper, their assortment is expanding in terms of sizes and types of section..
What is a profile pipe
Usually when it comes to pipes, we imagine a simple cylindrical object. This is how the communication routes surrounding us, carrying liquid and gas, look like. The circular cross-section of the pipe provides the best flow capacity with a minimum surface area. It is an ideal configuration for sensing pressure (whether internal or external). However, the round pipe does not perform well in all conditions. For example, it bends easily, which is very good for performing one-piece pipeline turns, but very unfavorable for the spatial rigidity of various structures. Profile pipes have completely different characteristics and advantages..
A shaped tube is a hollow tube-rolling product having any cross-section, except for a round one. Also, such pipes are called “bent closed-section profiles”, “professional pipes”. Most often, in a section, we will see a rectangle, square or oval, although modern rolling technologies make it possible to obtain more complex shapes..
In terms of physical properties, flat-oval pipes differ little from round ones, but they are characterized by increased decorativeness, therefore they are often used to create furniture, fencing elements, and design decoration of buildings. Another point is a large outer surface area with a significant decrease in the internal volume, which makes it possible to effectively use oval pipes in cooling systems where maximum heat removal from the carrier is required (coils, radiators). In addition, the oval profile is characterized by increased flexibility across the long side, therefore it is considered an arched.
Square and rectangular pipes perfectly withstand lateral loads, which is why they are used to create structural support systems and various elements of furniture. Structures of architectural structures are assembled from closed construction profiles, which are then sheathed with sheet materials, from which floor beams, trusses, racks, columns are made. Profile pipes for construction and general use are necessary for reinforcing PVC windows, for assembling boxes and sheets of metal doors. Small architectural forms (pavilions, change houses, booths, greenhouses), as well as frames, racks, advertising media are made from the professional pipe. It is almost always indispensable if you need to make a canopy or gate on the site. For many reasons, profile pipes are the best material for the manufacture of racks and bulkheads of a fence with filling the spans with a netting, corrugated board, forged sections.
Furniture pipes do not experience serious stress and, as a rule, are not exposed to negative environmental influences. Therefore, furniture shaped pipes are characterized by smaller cross-sectional dimensions, small wall thickness, and increased requirements for surface quality. Such a pipe can be seen in the construction of metal benches and swings, school desks and chairs, beds and other “public” furniture.
How are shaped pipes made?
The production of closed-section profiles is carried out in the same way as round pipes. On special pipe welding mills, sheet blanks (strips) are bent into a cylinder, and the resulting longitudinal seam is welded. Then the cylindrical pipe is driven through a system of additional rolls, where it is compressed with an effort of hundreds of tons to the required section. After that, the already shaped product is heated in order to “release” the metal inevitably stressed after mechanical action. Depending on whether the billet is heated during rolling, pipes are divided into cold-rolled and hot-rolled. Next, the quality of the seam and the geometry of the profile are checked, the products are cut to length and stored. The professional pipes are shipped to the consumer in bundled bundles weighing up to 5 tons. To protect the metal, pipes can be coated with grease and packed in metal boxes.
The closed-section profile is not always made from an electrically welded pipe. There are seamless shaped products, which are obtained by rolling on sizing rolls from a seamless round tube. One-piece drawn pipe has no seam, since it is made from a solid cylindrical billet – a “rod”. Seamless profile pipe is characterized by increased stability and tightness, while it is much more expensive.
The manufacturing process and design characteristics of oval pipes are regulated by GOST 8642–68. Construction square pipes are made according to GOST 30245-2003, GOST 8639-82, for rectangular profiles, GOST 8645-68 and GOST 30245-2003 are used. Thin-walled furniture pipes must meet a number of TU, for example, TU 14-105-737-2004. These regulatory documents unambiguously indicate:
- permissible geometric dimensions of the section;
- wall thickness;
- mass per running meter;
- corner radius;
- nominal length of products;
- marginal tolerances and quality-determining defects;
- the degree of resistance to mechanical stress;
- labeling requirements.
Thus, if you need to purchase a batch of rolled products to create durable, high quality products, the pipe assortment and compliance can be easily checked using a simple measuring tool..
Technological advantages of shaped pipes
Undoubtedly, the main advantage of a rectangular or square professional pipe is its substantial spatial rigidity, in comparison with a circular pipe. The thing is that such a closed profile has four stiffening ribs (two in each mutually perpendicular plane). When a profiled pipe is used as a supporting beam, and the load is applied at right angles to one of the planes, the bending resistance of the product will be about 30 percent higher than that of an equivalent round pipe of the same weight. This indicator will be close to the characteristics of a solid metal bar, since the main work on resisting bending and twisting loads is performed by its edges. If the vector of action of the force is known, then instead of a square section, you can use a rectangular one, placing the long side of the profile along the line of action (for example, for a beam on which gravity acts – vertically, and for a fence post – across the frontal plane of the sheathing). Using a rectangular pipe instead of a square one can reduce the material consumption of the product by about 10-20%.
Low material consumption is determined by the high spatial rigidity of metal structures made of a square shaped pipe. Due to the presence of internal cavities, savings on metal are, for example, in comparison with an I-beam or a rod, up to 25-30%. As a result, the assembled metal structures become one third lighter, which reduces the load on the foundations and load-bearing elements of the building. In addition, the bearing capacity of any frame with spans (beams, trusses) is calculated taking into account not only the working weight (for the roof, this is the roofing material + snow, and for the interfloor overlap – people + furniture). It also takes into account the fact that it must also carry itself. In other words, by reducing the weight of the structure, we increase the permissible payload – bearing capacity. The small mass of material and finished product makes it possible in most cases to do without the use of lifting equipment.
The strength of square pipes makes it possible to use a thinner cross-section of the profile in metal structures, which is not the least important for many structures. Due to the small area of the outer surface, the aerodynamic resistance of the product is reduced, therefore, the structure can withstand large wind loads. For the same reason, the skylights are increased, since rather narrow metal bulkheads are used. There is also savings on protective and decorative paints and varnishes..
Due to their flat surfaces, square and rectangular pipes are technically much easier to process than round ones. They are easier to prime and paint, the protective compounds adhere better to planes. Such metal products, for example, in comparison with an I-beam or channel, do not have zones that are difficult to access for processing, which has a positive effect on the corrosion resistance of the assembled product. Thus, the structure, where all surfaces are “in sight”, best meets the sanitary and hygienic requirements, the fire protection of metal frames and load-bearing elements becomes more effective..
The flat edges of the professional pipe provide it with excellent ergonomics, which are so appreciated in construction. These closed-section profiles are stably joined with any structural elements, it is very convenient to lay them along the bearing planes. Profile pipes take up a minimum of space near the base, do not form dead zones in the frames. It is convenient to screw self-tapping screws into them, they are easily sheathed with sheet materials.
Another important point is the convenience of connecting rectangular or square pipes, and, consequently, the increased installation speed. For example, to make a corner bend, there is no need to make curly cutouts on the workpiece, as if you had to join round pipes. Welding along a line is easier than in a circle, automatic and semi-automatic welding machines can be used, it is much more convenient to control the quality of the seam. Rectangular and square pipes are well fixed relative to each other with clamps. Before welding, the elements of the flat frame can be completely unfolded on any work surface and remain in place. The assembly of nodal joints can be carried out not only by welding, the presence of planes allows the use of mechanical options – tightening bolts, various couplings and fittings, overhead perforated plates in combination with self-tapping screws.
The presence of planes provides the professional pipes with good stability during storage and transportation, they can be packed in rectangular packs. Whereas round pipes, especially of large diameter, due to their ability to roll, are a source of increased danger – they are transported and loaded by special vehicles and laid out only in a “pyramid”.
Due to their geometry, square and rectangular pipes cannot withstand the same pressure as circular pipes of the same weight. Closed profiles have a smaller internal volume and, at the same time, a larger surface of contact (friction increases) with the transported material. Therefore, they are rarely used to create engineering communications..
How to choose a profile pipe
In order for the metal structure to have design performance characteristics and sufficient durability, it is necessary to carefully select the type of profile pipe. There are many classification criteria, and each of them reflects certain properties of a given product..
Mode of production
Depending on the characteristics of the production process, shaped pipes, like traditional round ones, are divided into: welded and seamless, hot-rolled and cold-rolled.
Hot rolled pipes(made of hot-rolled strip) – are construction and general-purpose ones, they are used to create street metal structures, as well as for the construction of building supports and load-bearing frames. Due to the high-temperature processing of the workpieces, they differ in some surface roughness, but they do not have internal stresses. Hot rolling allows the production of large diameter pipes (from 80×80) and with increased wall thickness. Since it is easier to deform alloyed and high-carbon steel at high temperatures, GK pipes often have anti-corrosion properties. Hot-rolled profile pipes are significantly cheaper than cold-rolled ones.
Cold rollingprofile pipes on high-tech mills allows the production of profiles of very high quality. This applies to surface cleanliness and accuracy of geometric dimensions (including low roughness of planes, small radius of rounding of corners). This type of pipe is chosen to create those products for which increased operational requirements are imposed. These are the so-called furniture pipes with small sides (from 10 to 40 mm) and a small wall thickness (up to 1.5 mm). Deformation of the workpiece without the use of high temperatures makes the profile pipe more resistant to internal or external pressure, while it is more flexible to bending.
Seamless pipeshave much greater strength than electric welded ones, since a poor-quality seam can be a weak point. In addition, hot-deformed seamless pipes are usually manufactured with a large wall thickness – up to several centimeters. Seamless pipes are characterized by high pressure resistance, ductility, good surface quality.
Profile pipes can be made from any carbon steel (GOST 380-2005 or GOST 1050-88) 08ps, 1ps, 2ps, 1sp / ps, 2sp / ps, St3sp / ps, St3sp / ps5, 10, 20, 35, 45, 15XM etc. For critical areas, professional pipes made of high-strength low-alloy steel 09G2S (GOST 19281–89) are often used.
Profile pipes coated with a thin layer of zinc have improved anti-corrosion properties, which rust 5-7 times slower than ordinary black pipes. Galvanizing occurs by immersing the pipe in a zinc melt or by spraying. Both the inner surface and the outer can be protected.
Profile pipes made of stainless steel, which are usually made of grades AISI 304 and AISI 316, slightly less often – from AISI 439, 430, 409, show almost absolute resistance to corrosion. They are mainly used to make architectural details of a building and not so often – to create bearing frames. The stainless steel profile pipe is characterized by abrasion resistance, heat resistance, a variety of finishing options (grinding, polishing, sandblasting texture, etching).
Whatever material is used for the production of rectangular / square pipes, the requirements for the geometry of the closed profiles will be identical.
This parameter is standardized by the current GOSTs according to which the pipes are produced. The optimal corner radius is 2S (double wall thickness), or 2.5S for pipes with walls over 2.5 mm thick. Depending on the manufacturing conditions and equipment characteristics, in fact, the corner rounding radius is often greater than the design one, which allows the manufacturer to make the profile pipes lighter and cheaper. Ultra-small round pipes look prettier, but they are heavier and more expensive than standard pipes. Note that corners that are too round (small stiffener) and too square corners (high dead weight) can reduce the bearing capacity of the structure..
The division of pipes by wall thickness is rather arbitrary. Here, it is necessary to take into account the ratio of the outer diameter to the thickness of the outer wall. Tubular rolled products are considered thin-walled if this ratio does not exceed 0.025, with an indicator of 0.05 – the pipe is called standard, a thick-walled product has a ratio of 0.1 and higher. In any case, the technology is such that the larger the pipe section, the greater the wall thickness. The main GOSTs clearly indicate which variants of this ratio are permissible for a particular method of pipe production (hot rolling or cold rolling). For example, a square pipe with a side of 180 mm and a wall of 4–14 mm can only be produced by hot deformation. The wall of closed profiles can vary in thickness within 1–12 mm, naturally, for more loaded structures (for example, for supports) pipes with more massive walls should be used.
Special mechanical properties
The classification of shaped pipes, depending on the mechanical and chemical properties of the workpiece, can tell us about the purpose of the pipe. For this type of metal products, the following marking is used:
- A – only mechanical characteristics are normalized (steel GOST 380-2005, earlier GOST 380-88);
- B – both mechanical characteristics and chemical composition are normalized (steel GOST 380-2005 or GOST 1050-88).
Class “B” standardization is usually assumed for large shaped pipes, as they are usually used for the manufacture of load-bearing building structures. At temperatures from -20 to +20, they are tested for impact strength. The same test is carried out after mechanical aging of the metal. Profile pipes are not subjected to hydraulic tests, but some manufacturers can carry out them on their own initiative, and, accordingly, guarantee the correct operation of products at a specific pressure. Such profile pipes are assigned the standardization category “D”.
It is obvious that profile pipes are very convenient for work, a truly versatile building material, which is simply irreplaceable in private construction. It is difficult to overestimate the technological and financial advantages that we obtain using a closed profile of a square or rectangular section. Experienced craftsmen have long made their choice.