If you look into the recent past, you can see that steel water and gas pipes were used everywhere, since they did not have a worthy alternative. Currently actively developed and implemented in all areas of the pipe from new materials. So, during the construction of modern high-rise buildings, water is supplied to the apartments through plastic pipes. This product has its advantages, but in many respects it is inferior to traditional steel water and gas pipes. This type of pipe is still in stable demand to this day and therefore is included in the range of production of metallurgical plants.
Classification and requirements for pipe products
Requirements, test procedure, production methods and chemical composition are established by GOST 3262-75. Steel water and gas pipes, in accordance with this state standard, are divided into three groups. Belonging to one or another group is determined by the production technology, by the used steel grades and their chemical composition, by the technology of heat and mechanical processing, by the method of protection against corrosion.
Pipe corrosion protection
According to the degree of corrosion protection, all pipe products are divided into the following types: pipe without a protective anticorrosive layer, galvanized water and gas pipe. Galvanizing can be done in two ways: galvanic and thermal diffusion. The second method requires large expenditures of resources and energy, which means that it significantly increases the retail price of products. Indeed, in order to obtain a diffusion layer of sufficient thickness, the water and gas pipe must be kept in an oven at high temperature for at least a day. Given current electricity prices, such processing will be very expensive. It is advisable to apply it only in the process of production of water and gas pipes for very responsible and strategically important facilities.
Electroplating is very fast, but the quality of this protection is much lower than with thermal diffusion galvanizing: the slightest careless touching of the pipe with any solid object can leave a scratch. With this scratch, steel (if it is not alloyed with more than 13% chromium) begins to corrode, as a result of which the entire surface swells.
Nitrogen may be used as a saturating element. The nitrided surface also resists corrosion under normal conditions. However, the nitriding process is rather complicated and expensive, which makes the production of gas and water pipes using this technology economically impractical. Just cleaning the surface from contamination will be very expensive. And without a high-quality cleaning of the surface, the nitriding process will not proceed properly, since dirt will prevent the diffusion of atoms or ions (in the case of ion-plasma nitriding in a glow discharge) of nitrogen deep into the metal.
Classification of pipe products depending on wall thickness
Metallurgical plants produce a wide range of water and gas pipes. So, depending on the purpose and operating conditions, pipes with ordinary wall thickness (2-4 millimeters), lightweight pipes (up to 2 millimeters) and reinforced are produced. The thickness of the latter is not limited and can be very significant. Such pipes, as a rule, are made seamless and designed for well drilling, operation in harsh conditions of the north, etc.
The minimum internal diameter of the gas pipe is 6 millimeters. The maximum value of the inner diameter is one and a half meters. Pipes with a maximum diameter are used when laying oil and gas pipelines, and with a minimum diameter - in the production of hydraulic equipment for machines and mechanisms. At the same time, it is erroneous to assume that stringent requirements are not imposed on pipes of small diameter. Quite the contrary - they must withstand incredible pressure during operation of the hydraulic cylinder and hydraulic pump.
Welded Pipe Production Technology
As mentioned earlier, pipes can be with and without a weld.
In the production of the former, ordinary steel sheet is used. On a special press, it bends into the pipe, and at the junction of the edges, the welded machine inflicts a seam at great speed. The technology has been worked out to the smallest detail, and the productivity of such pipes is simply huge. The speed at which the metal sheet is rolled, bent and welded is comparable to the speed of a bullet fired from a Makarov pistol. However, such pipes have a significant drawback - at high pressures, the weld can burst (especially if deviations from the process were allowed), and an accident occurs. The consequences of such an accident can be disastrous for both nature and man. Therefore, these pipes are not used for the construction of responsible highways and the production of highly loaded products of power engineering.
After completion of the welding process, the pipe section is not round. It is a closed loop of irregular shape. GOST 3262-75 "Steel pipes for water and gas" provides for the calibration and correction of the geometric shape of the section. To align the walls of the pipe, it is fed to a calibration mill. On it, the workpiece is attached to rotation, and it is pressed with considerable force to the rolls. At the outlet, the pipe has an almost perfect circle in cross section.
Seamless pipe technology
More recently (several decades ago), the production of seamless pipes was mastered. The technology is very complex, and equipment and supplies are expensive and imported from abroad (our engineers have not yet learned how to make carbide tips for extruding holes). But despite the fact that this type of product is very expensive, such pipes are in steady demand from oil producers and not only.
In general terms, the production process can be described as follows. The bar immediately after the rolling mill enters the hole extrusion section. At the same time, efficiency is important, since it is impossible to allow the bar to cool (this will lead to the need for re-heating it, and, therefore, to high costs). This operation is performed on a workpiece heated to a temperature above the recrystallization temperature. Only in these conditions does steel become malleable (fluid), and the structure of the deformed grain is dynamically normalized, which ensures good mechanical and operational characteristics.
Benefits of Using Steel Water Pipe
GOST regulates all the characteristics and parameters of pipe products without exception. And if we compare the performance of such pipes with what is offered by the manufacturer of PVC pipes and other materials, it becomes clear that metal pipes are beyond competition.
So, they can be operated at high temperatures, while maintaining their strength. This is very important in heating systems where high pressure steam is supplied through the pipes. The use of pipes made of other materials is simply impossible. They will melt or tear in a matter of seconds.
Additional alloying of steel can significantly increase the threshold of red breaking and mechanical strength of pipes.
Disadvantages of water pipes
GOST is the main source of useful technical information. And when studying the documentation for pipes, a technically competent person will not think for a long time about what disadvantages this product has. First of all, it should be noted that all steel structures (and pipes are no exception) are heavy. This significantly complicates the installation of products and puts forward certain requirements for the reliability of fasteners.
Metal alloys and steels have a very high coefficient of thermal conductivity. That means they give away heat. To increase the efficiency of the heating system, metal pipes when laying on the street must be insulated. Modern enterprises produce ready-made and insulated pipes of various diameters. Such products are quite high-tech and expensive, but it will save money and energy, which is especially important in our time.
How to install pipes
In accordance with GOST 3262, steel water-gas pipes can be connected either by welding or by means of threaded fittings.
When welding, the ends of two pipes are joined, and a weld is made at the joint. All work is manual, which means that they require a highly qualified welder (especially when it comes to laying an oil pipeline). The seam should be uniform, without non-metallic inclusions. Each welded joint is required to be tested by ultrasound.
The installation of the pipe system through fittings is used exclusively when working with pipes of small diameter. On the one hand, such work requires less skill from the contractor than when welding pipes. On the other hand, they will have to tinker more. Only one preparatory stage is what it takes: you must manually cut the thread using a die and a tap on each tube on one side and the other.
Pipe fittings
In general, the assembly of water and gas pipes (GOST 3262) with a thread in a single system is carried out in the following sequence:
- the thread surface is treated with sealant, after which a locknut is screwed;
- the fitting is screwed onto the pipe, and the nut is pressed against it with maximum tightening force;
- Sealant is applied over the fitting and nut (at the junction).
Instead of sealant, you can use wax. When wet, this material swells, and the water stops flowing.
Using copper pipes
Copper pipes began to be used relatively recently. Previously, GOST did not provide for such an opportunity, and copper products were produced exclusively for the purpose of instrumentation and precision engineering. But a little later, the advantages of using such pipes were appreciated, and corresponding changes were made to GOST at the initiative of a group of interested parties.
So, copper pipes are quite easy to bend, have a small diameter. Therefore, they easily hide in the gates. And due to their flexibility, you can use one long tube, bending it in the right places, instead of connecting many short segments, which requires a lot of time and labor.
Under normal conditions, copper is not exposed to the corrosive effects of a humid environment and water, which significantly extends its life and makes it very competitive, despite the fact that copper is a non-ferrous metal and is quite expensive.
How to recognize defective products
GOST 3262-75 “Water and gas pipes” establishes the criteria by which products must be classified as defective. Such pipes must not be used for their intended purpose. They must be sent to the manufacturer with the appropriate protocol (act). Violation of the geometric shape, expansion (swelling) of the pipe, burrs at the ends (the surface must be prepared for welding and have special bevels), peeling of the protective coating are not permissible. Also on the outer and inner surfaces should not be cracks.
Many enterprises carry out incoming inspection of incoming products. If technical means allow, it is necessary, in accordance with GOST 3262 "Water and gas pipes", to conduct a detailed analysis of the chemical composition of the steel from which the products are made, in order to exceed the permissible content of harmful substances (primarily sulfur and phosphorus).
But even if the organization does not have such expensive equipment at its disposal, the visual micro- and macroanalysis in any case must be performed. To do this, cut a small sample from the pipe. In this case, it is desirable to prevent its overheating in order to avoid phase transformations in the metal. One surface (several is better for an objective assessment) is subjected to grinding and then polishing using GOI paste (developed by the State Optical Institute, USSR). Alumina powder is well suited for this purpose. After polishing, the sample must be etched with special chemical reagents, as a result of which grain boundaries and phase components appear and can be observed on a metallographic microscope. In addition, porosity or non-metallic inclusions can be detected. If the content of carbon and harmful impurities does not comply with GOST 3262-75 “Water and gas pipes”, and there are inclusions and pores in the metal itself, then such a product is considered defective. Moreover, as a rule, not one or two pipes go to the marriage, but a whole batch.