If you look into the recent past, you can see that steel water and gas pipes were used everywhere, since there was no worthy alternative to them. Currently, pipes from new materials are being actively developed and introduced into all areas. So, during the construction of modern high-rise buildings, water is supplied to apartments through plastic pipes. This product has its advantages, but in many respects it is still inferior to traditional steel water and gas pipes. This type of pipe is in stable demand to this day and therefore is included in the range of production of metallurgical plants.
Classification and requirements for tubular 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 a particular group is determined by the production technology, by the steel grades used and their chemical composition, by the technology of thermal andmachining, according to the method of corrosion protection.
Protecting pipes from corrosion
According to the degree of protection against corrosion, all pipe products are divided into the following types: a pipe without a protective anti-corrosion layer, a galvanized water and gas pipe. Galvanizing can be done in two ways: galvanic and thermal diffusion. The second method requires a lot 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 a furnace at a high temperature for at least a day. Given the current electricity prices, such processing would be very expensive. It is advisable to use it only in the production of water and gas pipes for very responsible and strategically important facilities.
Electroplating is carried out very quickly, but the quality of such protection is much less than with thermal diffusion galvanizing: the slightest careless touch of the pipe with any hard object can leave a scratch. From this scratch, the steel (if it is not alloyed with more than 13% chromium) begins to corrode, causing the entire surface to swell.
Nitrogen can be used as a saturating element. The nitrided surface also resists corrosion well under normal conditions. However, the technological process of nitriding is quite complex and expensive, which makes the production of water and gas pipes using this technology economically unfeasible. Just one cleanupsurfaces from pollution will be very expensive. And without high-quality surface cleaning, 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 an ordinary wall thickness (2-4 millimeters), lightweight pipes (up to 2 millimeters) and reinforced pipes are produced. The thickness of the latter is not limited and can be quite significant. Such pipes, as a rule, are produced seamless and are intended for drilling wells, operation in the harsh conditions of the north, etc.
The minimum internal diameter of the water and 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 in the laying of 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 a mistake to assume that strict requirements are not imposed on pipes of small diameter. On the contrary, they must withstand the incredible pressure of the hydraulic cylinder and hydraulic pump.
Technology for the production of welded seam pipes
As mentioned earlier, pipes can be welded or not.
In the production of the first, the usualsteel sheet. On a special press, it bends into a pipe, and at the junction of the edges, a welded machine applies a seam at great speed. The technology has been worked out to the smallest detail, and the performance of such pipes is simply huge. The speed at which a 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 technological process were made), and an accident will occur. The consequences of such an accident can be catastrophic for both nature and humans. Therefore, these pipes are not used for the construction of critical highways and the production of highly loaded power engineering products.
After the welding process is completed, the section of the pipe is not round. It is a closed contour of irregular shape. GOST 3262-75 "Steel water and gas pipes" provides for the calibration and correction of the geometric shape of the section. To align the walls of the pipe, it is fed to the sizing mill. On it, the workpiece is given rotation, and it is pressed against the rolls with considerable effort. At the outlet, the pipe already has an almost perfect circle in cross section.
Seamless pipe technology
Relatively recently (several decades ago) the production of seamless pipes was mastered. The technology is very complex, and the equipment and consumables are expensive and imported from abroad (ourengineers have not yet learned how to make carbide tips for punching holes). But despite the fact that this type of product is very expensive, such pipes are in stable demand from oil companies and not only.
In general terms, the production process can be described as follows. The bar immediately after the rolling mill enters the area for punching holes. In this case, efficiency is important, since the bar cannot be allowed to cool down (this will lead to the need to reheat it, and therefore to high costs). This operation is performed on a workpiece heated to a temperature above the recrystallization temperature. Only under these conditions, the steel becomes pliable (fluid), and the structure of the deformed grain is dynamically normalized, which ensures good mechanical and operational characteristics.
Advantages of using steel water and gas pipes
GOST regulates all characteristics and parameters of tubular 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 used at high temperatures, while maintaining their strength. This is very important in heating systems where high pressure steam is supplied through pipes. The use of pipes from other materials is simply not possible. They will melt or tear in seconds.
Additional alloying of steelallows to significantly increase the threshold of red brittleness and mechanical strength of pipes.
Disadvantages of water and gas 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 shortcomings 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 thermal conductivity. This means they give off heat. To increase the efficiency of the heating system, metal pipes must be insulated when laying on the street. Modern enterprises produce ready-made and insulated pipes of various diameters. Such products are quite high-tech and are not cheap, but they will save money and energy resources, which is especially important in our time.
How pipes are installed
In accordance with GOST 3262, steel water and gas pipes can be connected either by welding or by threaded fittings.
When welding, the ends of two pipes are joined, and a weld is made along the joint. All works are manual, which means that they require high qualifications from the welder (especially when it comes to laying an oil pipeline). The seam must be uniform, without non-metallic inclusions. Eachthe welded joint must be tested by ultrasound.
Installation of a pipe system using fittings is used exclusively when working with pipes of small diameter. On the one hand, such work requires less qualification from the performer than when welding pipes. On the other hand, they will have to tinker with more. Just one preparatory step is worth it: you need to manually cut the threads with a die and a tap on each tube from one side and the other.
Procedure for connecting pipes with fittings
In the general case, the assembly of water and gas pipes (GOST 3262) with a thread into a single system is carried out in the following sequence:
- the surface of the thread is treated with sealant, after which the locknut is screwed on;
- a 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).
Wax can be used instead of sealant. When wet, this material swells and water stops flowing.
Using copper pipes
Copper pipes have been used relatively recently. Previously, GOST did not provide for such a possibility, and copper products were produced exclusively for the purposes of instrumentation and precision engineering. But a little later, the advantages of using such pipes were appreciated, and appropriate 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 gates. And due to their flexibility, you can use one long tube, bending it in the right places, instead of connecting many short lengths, which requires a lot of time and labor.
Under normal conditions, copper is not exposed to the corrosive effects of wet environments and water, which significantly extends its service 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 (bloating) of the pipe, burrs on the ends (the surface must be prepared for welding and have special chamfers), peeling of the protective coating are not allowed. Also, there should be no cracks on the outer and inner surfaces.
Many enterprises carry out input control of incoming products. If technical means allow, then 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 levels of harmful substances (primarily sulfur and phosphorus).
But even if the organization does not have such expensive equipment at its disposal, the visual micro- andmacroanalysis in any case must be performed. To do this, a small sample is cut from the pipe. In this case, it is desirable to prevent its overheating in order to avoid phase transformations in the metal. One (preferably several - for an objective assessment) surface is subjected to grinding and then polishing using GOI paste (developed by the State Optical Institute, USSR). For this purpose, aluminum oxide powder is well suited. After polishing, the sample must be subjected to etching 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 recognized as defective. Moreover, as a rule, not one or two pipes go into marriage, but a whole batch.
