Round steel pipes are used in many industries: in the construction of bridges, gas and oil pipelines, in residential buildings, factory floors and in many other places and industries. The range of manufactured products is very extensive, they may differ in diameter, method and material of manufacture. All parameters of manufactured products are regulated in accordance with GOST.
Main characteristics of pipes of round section
The main parameter by which the preliminary selection of pipes for application is carried out is the diameter. In assortments for round pipes, the following types of diameters are distinguished:
- The outer diameter is the main dimension in determining the possibility of using the product in various areas of industry and everyday life.
- The inner diameter characterizes the throughput of the pipeline. The nature of the flow and the pressure loss during the movement of the liquid depend on the value of this size.
- Conditional diameter. This size characterizes the approximate throughput of pipes and may be the same for different sizes. For example, for the standard size 45×2.5 and 43×1.5, the nominal diameter is Dn=40.
- Nominal diameter. Estimated value when selecting the required parameter.
Applicability of products of various diameters
Depending on the outer diameter, the products can be used in the following areas:
- For heating and hot water supply systems of residential and industrial buildings, steel pipes with a diameter of 40-50 mm are used.
- In hydraulic systems of working bodies of machines and road equipment, depending on the amount of fluid supplied, the diameter can be from 8 to 50 mm.
- In large apartment buildings for supplying cold water, the diameter of the pipelines used is up to 150 mm.
- In the oil, gas and chemical industries, products with diameters up to 273 mm are used for internal transportation of raw materials.
- Large city boiler houses for supplying heating to the house, and water supply companies use diameters up to 325 mm to supply water.
- Sewer pipes have a size of 530-1020 mm in diameter.
- In large systems for transporting gas and oil, large sizes of 1020 mm and more can be used.
- Pipes are widely used in construction for driving piles, foundations and bridges. The diameter of the applied products is from 650 mm.
The actual dimensions of the products used may differ from the tabular ones, and depend on the design features of the pipeline system used.
Wall thickness and other parameters
The wall thickness depends on the method of manufacturing the product and is:
- for hot-rolled — 2.5 … 75 mm,
- for cold-rolled — 0.3 … 24 mm,
- for welded — 1 … 32 mm,
- for welded according to the technology of spiral rolled products — 3.5 … 25.
Weight per meter. To determine the mass, the assortment table from GOST is used. If it is necessary to calculate the mass of 1 linear meter, then the calculation is made according to the formula:
- P is the mass of one linear meter, in kg.
- D is the outer diameter, in mm.
- S is the wall thickness of the product, in mm.
- 40.5 is a coefficient depending on the specific gravity.
The products can also be used as building metal structures. For the force calculation of such structures, it is necessary to determine the moment of inertia and the radius of inertia. The values of these quantities can also be taken from the GOST tables or determined by the formula:
J=∏D³*S/8 and j=0.353D, where
- J is the moment of inertia, in cm4,
- ∏ is Pi equal to 3.14
- D is the outer diameter, in cm.
- S is the wall thickness of the product, in cm.
- J is the radius of gyration, see
Another parameter characterizing the possibility of using a pipe in building structures is the circular moment of resistance. Designation Wx and Wy. For a round pipe, these parameters are the same for the OX and OY axes. This parameter can also be determined by the formula or taken from the table.
Types of pipes by production method
There are the following methods of pipeline production: hot-formed, cold-formed, electric-welded. Dimensions and maximum deviations of products, materials of manufacture are regulated by assortments for round steel pipes, different assortments for each production method:
Seamless hot-formed steel pipes GOST 8732
The production of pipes takes place in three stages. At the beginning, in a round billet heated to 900-1200 degrees, a hole is pierced on special machines, as a result, a sleeve is obtained. Next, the sleeve is rolled into a draft pipe, and the last stage is sizing, rolling with final dimensions in terms of thickness and diameter.
The dimensions of the products obtained by this method of production can be: outer diameter 16-630 mm, wall thickness 1.5-50 mm. The blanks of products are divided into several groups, depending on the material used for manufacturing:
- A — the mechanical properties of the product are normalized.
- B — the chemical composition is regulated during manufacture.
- B — mechanical properties and chemical composition are simultaneously regulated;
- D — the chemical composition is normalized and the mechanical properties are checked on prototypes;
- D — the value of the test pressure during verification is regulated.
Pipes steel seamless cold deformed in accordance with GOST 8734
For rolling, round steel billets are used. The workpiece is heated in special furnaces to the temperature of the beginning of crystallization to obtain the necessary plasticity. Then it is stitched and enters the rolling mill, where the rough dimensions of the product are formed with the help of rollers. The last operation is sizing and cutting to a certain length.
Unlike a hot-formed pipe, a cold-formed pipe receives additional heat treatment during calibration, which makes such products stable and durable.
Cold-formed products are divided into the following categories, where the main criterion is the ratio of the diameter D to the wall size S:
- Particularly thin-walled, with a D / S ratio greater than 40. If the dimension D = 20 mm or less, the dimension S = 0.5 mm or less.
- Thin-walled, with a D / S ratio of 12.5 and less than 40. In addition, pipes with D \u003d 20 mm. and less, at S=1.5 mm, and less.
- Thick-walled, with a D / S ratio of 6 to 12.5.
- Particularly thick-walled with a D / S ratio of less than 6.
Thin-walled and extra-thin-walled pipes are used in various hydraulic systems, automotive engines, industrial refrigeration systems, as well as in the medical and food industries. The main application of thick-walled pipes is in the oil and gas industry.
Electric-welded steel pipes according to GOST 10704
The manufacturing technology includes several stages, which are combined into one continuous process:
- Sheet cutting. It is performed on high-precision machines and allows you to get blanks of the same size.
- To obtain an endless tape, the strips are welded together, previously passed through a system of rollers to eliminate surface defects.
- The resulting workpiece is passed through a system of horizontal and vertical rollers, with which the product is formed.
- Edge welding is performed using high-frequency welding. The edges of the workpiece are heated by an inductor to the melting temperature, and then squeezed by crimping rollers. Another way, when the edges are heated with a high frequency generator, current is applied to the edges using contacts.
- Calibration and deburring. The workpiece is cooled and then passed through sizing rollers to eliminate ovality and ensure the required dimensions.
- Product cutting. The blanks are cut to the required size.
- Quality control of manufactured products is carried out in three ways: weld inspection, high water pressure test and flattening. To control the weld, the ultrasonic method is mainly used. The flaw detector is located directly on the line after the welding operation. 100% of products are subject to control. 15% of the products from the batch are subjected to hydrotesting. And two products from the batch pass the flattening test.
Electrowelded pipelines are widely used in the laying of engineering networks that can withstand heavy loads and pressures. Products with a diameter of 1200 mm. used in the installation of almost all main gas pipelines and oil pipelines.
Materials used in the manufacture
The materials used in the manufacture of hot-formed pipes are specified in GOST 8731, and for cold-formed pipes in GOST 8733. In the manufacture of such products, blanks are used from ordinary carbon steel according to GOST 380, high-quality carbon structural steel according to GOST 1050, and structural alloy steel according to GOST 4543. In the manufacture of electric-welded pipes, all specifications for the materials of products are specified in GOST 10705.
In industry, seamless pipes made of stainless steel are widely used. They are used in instrumentation, in the manufacture of automobiles, in the chemical industry and in many other areas of production.
The entire range, as well as the technical specifications of round stainless steel pipes, is established in GOST 9941. According to the production method, they are manufactured in a cold-formed or hot-formed way, of the following sizes:
- with outer D 16-53 mm, wall thickness S 2-5 mm;
- if D is 53-73 mm, then S is from 4.5 to 10 mm;
- diameter D 84-80 mm, wall S from 11 to 15 mm;
- for diameters D 140-219 mm, S from 28 to 32 mm.
To protect stainless pipes from corrosion, it contains chromium, which is made resistant to aggressive chemicals. The surface of the resulting finished products can be matte or mirror, depending on the method of manufacturing pipelines.
Fluid head loss when moving in round pipes
When transporting liquids in pipelines, pressure losses occur, which depend on the following factors:
- roughness of the inner surfaces of the pipe,
- losses during the passage of the narrowing of the section in taps, adapters and other fittings,
- losses during sharp 90-degree bends in the pipeline,
- in addition, the head loss depends on the viscosity of the fluid.
There are two modes of fluid flow: laminar and turbulent. Laminar is when the movement of fluid in pipelines occurs without mixing particles. With turbulent, there is abundant mixing and rotational movement of fluid particles. The flow transition from laminar to turbulent occurs when the Reynolds number Re>2300.
The Reynolds number depends on the flow velocity, internal diameter and viscosity of the fluid and characterizes the mode of fluid movement. When calculating the parameters of pipelines, it is necessary that the calculated Reynolds number be Re<2300. At the same time, there is less loss and power consumption of pumps for fluid movement.
For joining sewer and water lines, a socket connection is used. To do this, a special extension is made at the ends of the pipes, where the other end is inserted. The tightness of the connection is ensured in various ways:
- Sealing with cement. This method is used when docking sewer systems. First, the gap is sealed with tow, and then the cement mortar is poured.
- Sealed with a rubber sealing ring. Before assembly, the ring must be lubricated with glycerin or soapy water.
- Adhesive connection. The ends are treated with sandpaper to roughen. Then smear with adhesive solution inside the socket and the end of the pipe. Both products are pressed tightly and held until the adhesive hardens.
- Connection by welding.
The socket joint provides a reliable connection, however, in some cases, a so-called additional seal is installed, especially for cast-iron sewer systems.