Existing pipeline repair methods
Polyethylene pipes HDPE (PE 80 and PE 100) are actively replacing the usual pipes made of steel and cast iron in almost all areas of pipeline application. Long service life (more than 50 years), ease of piping, low weight make synthetic polymer piping a favorite. Pipes made of polyethylene, polypropylene and PVC have practically replaced traditional pipes in water supply, gas supply, sewerage and in protective duct systems for electric cables.
Specialists of LLC "Elf" carry out mainly (which is not surprising, trying to keep up with technical progress and taking into account the core activities of the enterprise) installation polyethylene pipes pipelines from HDPE pipes (PE 100 and PE 80) in various ways, taking into account the nature and purpose of the pipeline, the applicability of various methods in specific conditions and the place of welding. The head of the enterprise or the Chief Engineer visits the site together with the Customer's representative, identifies significant points, then the estimate department makes the necessary calculations, after which an estimate is made for the cost of work.
When installing pipelines, HDPE pipe sections (PE 100 or PE 80) are interconnected by HDPE fittings. There are two types of fasteners: detachable - allows disassembly during operation, one-piece - cannot be dismantled. Depending on the choice of connection, different installation methods are used.
Installation methods for polyethylene pipes:
Butt welding. The method is used to connect products with the possibility of placing bulky welding equipment. The process consists in heating with a heating element, followed by pressure connection of the molten ends of the welded HDPE pipe segments (PE100 or PE80). During the removal of the heater from the connection zone of the heated parts, a technical break occurs. The shortest possible pause will not lead to a decrease in temperature and the ingress of contaminants that affect the quality of the connection. When cooling, the strength of the joint increases.
Electrofusion welding. The process is carried out with special equipment using electrofusion (electrofusion, thermistor) HDPE fittings made of PE100. This method is used in cramped conditions where butt welding of HDPE polyethylene pipes is inconvenient, for example, in wells or when repairing a damaged HDPE pipeline. The couplings are equipped with a wire heating element, which, upon reaching a certain temperature, begins to melt the polyethylene in the contact zone. After cooling, a highly hermetic joint is formed at the junction. Modern electrofusion welding machines allow you to automatically set the welding parameters (voltage and time) for each specific fitting.
With compression fittings.
The cost of electrofusion welding of pressure polyethylene pipelines for water supply and sewerage.
HDPE pipe diameter | Price per joint |
14 000 rub. |
63 | 500 rub. | |
75 | 550 rub. | |
90 | 650 rub. | |
110 | 900 rub. | |
125 | 1200 rub. | |
140 | 1350 rub. | |
160 | 1550 rub. | |
180 | 2000 rub. | |
200 | 2300 rub. | |
225 | 2500 rub. | |
250 | 3300 rub. | |
280 | 3700 rub. | |
315 | 4400 rub. | |
355 | 5500 rub. |
The minimum cost of work performed in one work shift 20 000 rubles (every 40 km from MKAD - plus 3000 rubles) |
400 | 6600 rub. | |
450 | 7700 rub. | |
500 | 9300 rub. |
The cost of butt welding of pressure polyethylene pipelines for water supply and sewerage
HDPE pipe diameter | Price per joint |
The minimum cost of work performed in one work shift* 16 000 rub |
63 | 600 rub. | |
75 | 660 rub. | |
90 | 900 rub. | |
110 | 1100 rub. | |
125 | 1450 rub. | |
140 | 1600 rub. | |
160 | 1800 rub. | |
180 | 2450 rub. | |
200 | 2750 rub. | |
225 | 3000 rub. | The minimum cost of work performed in one work shift 20 000 rub. (for every 40 km from the Moscow Ring Road - plus 3000 rubles) |
250 | 3750 rub. | |
280 | 4300 rub. | |
315 | 5000 rub. | |
355 | 6000 rub. | The minimum cost of work performed in one work shift 24 000 rub. (for every 40 km from the Moscow Ring Road - plus 3000 rubles) |
400 | 7200 rub. | |
450 | 8300 rub. | |
500 | 10000 rub. |
* The table shows the cost of welding work only - i.e. it means that the team of welders performs only work directly related to the welding process, such as: cleaning, degreasing, positioning and checking the geometry of the welded HDPE pipe sections and directly carrying out the welding process. But they do not participate in any way in preparing the trench, backfilling the sand cushion, transporting pipes and fittings to the place of welding, digging a pit, moving interfering objects and reinforced concrete products, and similar processes; the care of carrying out such work lies with the customer or the customer additionally pays for auxiliary workers who are hired by agreement of the parties by the welding contractor.
All prices in the table are based on the welding of polyethylene pipelines for water supply and sewerage.
PRICES FOR WELDING POLYETHYLENE PIPELINES FOR GAS SUPPLY ARE CONSIDERED INDIVIDUALLY IN EACH CASE!
*Working shift - 7 hours + 1 hour mobilization.
Organization of laying of polyethylene pipelines from HDPE pipes (PE 100 or PE 80)
When installing a pipeline made of polyethylene HDPE pipes, the following rules must be observed:
- Observance of the laying depth. To avoid damage to a pipeline made of HDPE polyethylene pipes by a temporary load, the passage of utilities should be 0.2 m more than the depth of soil freezing (in the Central region - 1.6 m).
- Leveling the bottom of the trench. Before laying the system, the bottom of the trench is leveled. A sandy layer 15-25 cm thick is laid out in the soil with solid inclusions at the base of the trench.
Benefits of contacting Elf LLC:
A wide range of services. Extensive experience in this area allows us to troubleshoot problems of a very different nature: local damage to the pipeline; crushing, partial or complete rupture; leak in knots and much more.
Drawing up a budget. Drawing up a detailed report on the cost of all pipeline repair work that will be done.
Repair efficiency. The professional team of Elf LLC performs all technological operations in a short time with consistently high quality. This is especially true in the event of accidents, when it is necessary to restore or replace, for example, water supply networks, with minimal time.
Reliability of work performance. Our highly qualified specialists use only modern equipment in their work. This allows us to guarantee the high quality of the services provided, even when working in particularly difficult conditions.
If you need repair of pipelines, please contact our company by phone numbers listed in the section"Contacts" . The staff will acquaint you in more detail with the types of work that we offer, as well as draw up an estimate indicating the cost of all services for the repair of your pipeline.plumbing
Works on the arrangement of external engineering networks and communications
Construction of external water supply networks;
. installation of external water supply;
. hot and cold plumbing;
. installation of a fire water pipeline;
. installation of gate valves, valves and fittings;
. design of the water supply system;
. installation of pumping equipment;
. wiring of water supply systems;
. flushing water supply;
. installation and maintenance of water treatment systems;
. device for inputs of external water supply;
. supply of necessary equipment;
. installation of fire hydrants;
. repair of water supply systems (elimination of problems with existing and dismantling of emergency sections of the water supply system, replacement of water supply pipes);
. commissioning works;
. service maintenance of water supply systems.
.
Plumbing works
Installation of sewerage and cleaning systems;
. arrangement of storm wells and chambers;
. installation of external sewer networks;
. installation of storm gravity sewers;
. cleaning of sewers and sewer channels;
. installation of septic tanks;
. automated sewer pumping stations;
. engineering networks of pressure (forced) sewerage;
. installation of sanitary appliances and household equipment;
. selection of the optimal composition of equipment (pipes, valves, adapters, couplings, fittings) and its supply;
. construction of sewer wells and drains;
. sewer repair and diagnostics;
. ensuring warranty repair of the sewer system;
. subscriber and service maintenance (cleaning of sewerage from blockages, repair, replacement, cleaning of sewerage, etc.);
Works on the arrangement of internal engineering systems and equipment
- The device of thermal systems with a heat carrier temperature up to 115 degrees. С (including from polymeric materials)
- Installation of plumbing systems and equipment (including those made of polymeric materials)
- Device sewer systems and equipment (including those made of polymeric materials
- Installation of sanitary appliances
- Installation of metering and control devices
- Device gas systems and equipment installation
- Arrangement of technological pipelines
An analysis of publications and a patent search for repair methods for damaged main and distribution pipelines made it possible to divide all existing methods into the following four groups according to technological features and equipment used:
- Repair methods associated with the complete replacement of the defective section of the pipeline with a new pipeline.
- Repair methods that involve sealing the damaged section of the pipe from the outside.
- Repair methods in which sealing is carried out from the inside of the pipeline.
- Repair methods according to the so-called "pipe in pipe" type, in which a new pipe of a smaller diameter is inserted into the damaged section of the pipeline.
The first group of repair methods is still a traditional technology. Given that the repair associated with the replacement of the damaged section with a new pipe is quite expensive, its expediency follows from the presence of large defects in the pipeline, or its complete wear. The considered methods are easier to implement for open pipelines. Here, the main difficulty is cutting off the pumping product in the defective area and removing its residues from the welding zones. In the case of underground pipelines, a complete opening of the damaged area is generally required, which significantly increases the complexity of the methods, especially in hard-to-reach places.
There are technologies for replacing a defective section of a pipeline with a new pipeline without opening. The essence of these technologies is that the old pipe is destroyed with the help of special devices, and its crushed segments are either removed or pressed into the ground with a conical expander, thereby freeing up a passage for laying a new pipe. The destruction of worn pipes is carried out in two ways - dynamic and static. The dynamic method is carried out using a pneumatic punch moving inside the old pipeline. The static method of pipeline destruction is carried out using a cutting working body, made either in the form of a conical head equipped with a flat knife made of high-strength steel, or in the form of a roller knife (cutter) with an expander. The drive of the cutting working body is carried out using special equipment. Currently, equipment for trenchless repair and replacement of pipelines is manufactured by more than twenty foreign companies. There is no serial production of such equipment in Russia. At the Odessa plant of construction and finishing machines, complexes of the MPS-01, MPS-01-01 type are manufactured to replace pipes with a diameter of 150-250 mm.
As you can see, these technologies are quite complex; they require complex and expensive mechanisms for the destruction of the old pipe and devices for pushing them. The defective section of the pipeline must be dilapidated for its complete and unhindered removal and, moreover, not very curved and extended.
When repairing underwater pipelines, the complexity of the considered methods belonging to the first group increases even more, which is associated not only with the release of the defective section of the pipeline from the soil, but often with its rise above the water level.
Solve the problem of mass repair of main pipelines with corrosion and other damage, focusing only on the technology of electric arc welding with the replacement of damaged sections throughout Russia for short term practically impossible and cost-effective. Even with the availability of pipes and financial resources for the reconstruction, the replacement of all worn-out pipelines in the country will take decades. In addition, from the point of view of labor and material consumption, as well as manufacturability, the use of electric arc welding is not always advisable, so it is mainly applicable for reconstruction.
Despite the noted shortcomings, the technology under consideration is quite acceptable and effective for emergency repair of pipelines, which have access to damaged areas for their removal and replacement.
To eliminate local and minor corrosion, erosion and other defects, methods of restoring pipelines from the outside have become widespread. Compared with the previous group, these methods are less expensive and require less time to implement. However, the disadvantage associated with the opening of underground pipelines remains. Sealing from the outside can be carried out by various methods, depending on the diameter of the pipeline and the material from which it is made, as well as on the composition and parameters of the transported medium.
Well-known as a temporary, but quick measure to eliminate the leakage of liquid or gas from metal or plastic pipes, methods using metal clamps, couplings, and other clamping devices. As a sealant, ductile metals, rubber seals, sticky synthetic tape, clay plaster are used. In the presence of small cracks, repairs can be made using welding (for gas pipelines - with shutting off the gas supply and observing the relevant safety rules). As a patch, half-couplings can be used, which are welded to each other with longitudinal seams, and with annular seams with the pipeline, or couplings with through holes for welding to the pipe. In some cases, a sheathing is constructed around the defect and a hardening polymer material is injected into the cavity between it and the pipeline. In this case, the role of the coupling is played by a heat shrink tape.
Among the many ways to repair pipelines from the outside, belonging to the 2nd group according to the proposed classification, the leading place was taken by the method of eliminating defects using the “cold” welding technology using polymer composite materials. Based on the results of many years of research and field tests, Gaznadzor LLC tested various materials, identified effective technologies, developed structures with a guaranteed service life of up to 20 years for the repair of pipelines and equipment in the oil and gas industry using the "cold" welding method. Together with specialized institutes, Gaznadzor LLC developed departmental guidance documentation, which was approved by Gazprom and put into effect on October 1, 2000. In accordance with technological map repair, the surface of the pipe section with a defect is prepared, the pipe geometry is restored using a polymer composite material (PCM). Then, using a PCM adhesive, a glass-polymer composite tape (SPCL) is applied to it, which has a memory of the pipe diameter and strength properties that are higher than those of metal. Installation and fixing of the tape is carried out on the gas pipeline only when the pressure drops by at least 30% of the working one and without stopping the operation of the gas pipeline. The pressure drop is regulated by regulatory and technical requirements in order to ensure the safety of the repair, as well as to enable the repair structure to work. To achieve the necessary adhesion, the SPCL laid on the defect using a template corresponding to the curvature of the outer surface of the pipe is fixed with various clamping devices that provide the necessary force.
The described methods refer to open methods, which, in cases of repairing network gas pipelines in cities, towns or near them, require the opening of the roadway, lawns, the demolition of green spaces, the closure of city highways, followed by reclamation and restoration of disturbed landscaping. As a result, there is a violation of the usual rhythm of life in areas adjacent to the place of work. Thus, the considered group of repair methods is uneconomical due to significant costs.
Methods for repairing pipelines from the inside are trenchless. Sealing can be carried out by different methods. Repair devices are known that make it possible to introduce annular lining liners, special bushings, seals in the form of a flexible patch into the restored pipe, with a rapidly hardening composition with increased adhesiveness applied to its surface or in the form of a hose-like foil.
The largest number of methods in the 3rd group are methods in which the pipeline is sealed by applying a protective restorative coating to its inner surface. Such a coating is obtained in the following way. After preliminary cleaning and drying, a hardening material is injected into the defective section of the pipeline, and then a former is pulled through it, which displaces excess material, and on the inner surface of the pipe, a uniform protective layer of this material hardens over time. In some cases, the protective coating material is placed on the surface of an elastic sheath, which is introduced into the damaged area of the pipeline and inflated. The material is pressed against the inner surface of the pipeline. After the material has cured, the elastic sheath is removed.
In cases of repair by the considered methods of pipelines of large diameters, special devices are offered for applying coatings to the inner surface of pipes. These devices contain a transport module, mechanisms for squeezing out the polymer filling mixture, mechanisms for its radial supply and application to the inner surface, and heating elements for polymerization.
Despite the main advantage of these methods, which is repair without opening the pipeline, they have the following disadvantages that limit their use, especially in the repair of gas pipelines, where high reliability and quality are required.
- The need for sophisticated equipment.
- The need to get the polymer material in the right place and ensure full and reliable contact.
- The strength of the polymer protective coating in cases of high pressure and significant defects, as well as high wear of the pipe, may be insufficient.
- The impossibility of quality control of repair work in the course of their implementation.
- The impossibility of high-quality repair of pipelines laid in soils with high humidity, as well as underwater pipelines.
Methods for repairing pipelines of the "pipe in pipe" type are relatively cheap and fast trenchless technologies, and these advantages often outweigh their main disadvantage - a decrease in the flow area of the pipeline.
Usage metal pipes as repair pipes due to their high bending rigidity, it is possible only in cases where the worn section of the pipeline is practically straight, and there is also space for the formation of shafts of the required length for the introduction of repair pipes. Due to the noted limitations, repairs using metal pipes are carried out mainly on large-diameter pipelines. With an increase in the length of the repaired section of the pipeline, even if it has a slight curvature, the force required to pull the repair pipes increases. In order to reduce this force, centering guide roller elements are used. The support elements are proposed to be placed on the surface of the repair pipe along a helical line, and when an axial force is applied to the pipe, it is necessary to give it a rotational motion. In some cases, to facilitate installation, the repaired section of the pipeline is filled with water, and a new pipe, supported by a special floating pipe, or pontoons, is floated. After laying, water is removed from the pipeline. As a traction device, a winch and a cable are usually used, pulled through the repaired pipeline from the second opened end of it. Instead of this traditional method of moving sections of repair pipes, pressure can be applied to the inside of these sections, the front end of which is temporarily closed with a plug.
The use of plastic, in particular, polyethylene pipes for repair in this way expands its capabilities, since such pipes, compared to metal ones, have greater flexibility and lighter weight, which means they allow repairing pipelines that are longer and have a sufficiently large curvature. However, if the issue of obtaining the necessary flexibility of a plastic pipe is solved by reducing the wall thickness, then problems arise associated with a loss of strength both for abrasion when pulled into a repaired pipeline, and strength when loaded with internal pressure. This is the main disadvantage of using plastic pipes. It is impossible to prevent abrasion of a repair pipe against the walls of a worn, corroded pipeline, and to ensure strength when pumping a medium under pressure, an additional complex technological operation is required to fill the annulus with plugging material, for example, foam cement.
There are so-called "stocking technologies" of repair, which are assigned to the 4th group, since they are associated with pulling special sleeves into the repaired pipeline, sometimes called stockings. As a result, however, these methods are close to the methods of sealing pipelines from the inside with various polymer compositions.
As a stocking, for example, a synthetic sleeve with glue applied to its outer surface is used. After pulling the sleeve, it is pressed against the inner wall of the pipeline with special rollers or by applying pressure inside.
In other methods, combined sleeves made of composite materials are offered as a protective coating. These sleeves are introduced into the pipeline. Then, directly into them or into the auxiliary hose, a heated gaseous or liquid medium is supplied under pressure. The combined sleeve pressed against the inner surface of the pipe polymerizes and forms a sealed protective film. The auxiliary ru-kav is removed.
Quite close to the “stocking” is the “U-liner” technology, in which a U-shaped (maybe of a different shape) in cross section is pulled into the pre-cleaned repaired pipeline, plastic, most often polyethylene, with its subsequent straightening with the help of a coolant of a certain temperature and the formation of a new one-piece plastic pipeline.
The advantage that distinguishes "stocking technologies" and "U-liner" technologies among the methods of the 4th group is that the flow area of the pipeline is practically preserved. but they are not without the shortcomings listed in relation to the methods of the 3rd group. In addition, one more disadvantage, already indicated for plastic pipes, is added - the possibility of damage to the sleeve or plastic pipe against the walls of a worn pipeline when pulled. And this drawback manifests itself the more, the greater the curvature of the defective section of the pipeline and the greater its length.
Noteworthy are the methods of repairing curved pipelines, in which corrugated pipes are used as a repair pipe. Corrugated pipes or sleeves have low bending stiffness, so they can be pulled (pushed) into. defective sections of highly curved pipelines, even containing bends and bends. The reason limiting the use of corrugated pipes is the same as for plastic pipes - their low strength. This refers not only to the pressure load strength, but also to the contact strength and tensile strength required when pulling into the repaired pipe. This drawback is eliminated by supplying them with an external wire braid.
The described methods of repair of all four groups, with the exception of the methods of repair of the 2nd group, for minor damage require a mandatory stop of the pumping of the transported product. At the same time, there are quite a few situations when, despite a detected defect or through damage to the pipeline, it is impossible to stop pumping due to the emergence of significant technological and social problems (metallurgical, glass industry, petrochemistry, cooling system reactors of nuclear power plants, power supply for heating boilers in winter time etc.).
There are ways to repair damage to pipelines without stopping pumping using cold tapping and bypass line installation.
The method of emergency repair of the pipeline without stopping the pumping includes two main stages (figure below):
1. Emergency shutdown of the damaged section of the pipeline.
Scheme of repair work with installation of a bypass line
a - installation of blocking devices to cut off the damaged area from the main line; b - bypass installation; c - removal of the damaged area and its replacement with a new one; d - dismantling of blocking devices and commissioning of the pipeline
2. Laying and inserting a temporary bypass line for continuous pumping.
The main restoration work on replacing the pipe section is carried out in the usual rhythm, which contributes to improving the quality of installation work. Simultaneously with the start of emergency recovery work to open the pipeline section, collect and pump out the flowing oil product, blocking devices are installed on both sides of the removed section of the pipeline (without emptying it) to cut off the damaged section from the main line, for which two types of complex and responsible operations:
- Cutting holes in the pipeline.
- Entering through them overlapping devices.
To do this, at the point of entry of the blocking devices, two branch pipes or split tees are welded to the pipeline, in the flanges of which there are special grooves for installing plugs after the completion of repair work. A special stop valves, to which a mechanism for cutting a hole is mounted. The design of the mechanism allows you to cut holes in the pipeline, which is under the pressure of the pumped product. Holes are drilled with a cylindrical tubular cutter with an end working part. The cutter must be installed very precisely along the axis of the intended hole, and the frame is attached to the flange.
The milling spindle is equipped with a special device that holds the cut piece of metal and allows it to be removed. rotational movement milling cutters and its feed are provided by a pneumatic or hydraulic drive built into the frame. After cutting the holes, the mechanism is dismantled, the fittings are closed and a device for inserting overlapping devices is installed in its place. The blocking device is a plug in the form of a ribbed cone, mounted on rods, and allows you to keep the working pressure of the liquid in the pipeline.
After cutting holes in the pipeline and dismantling the drilling device, a bypass is connected to the valves, through which the flow of the pumped product is directed. The damaged section is removed and replaced with a new one, then the blocking devices are dismantled, the branch pipes are plugged with special segment plugs, the valves on the bypass line are closed, and the oil product flow is directed through the main pipeline.
In order to comply with safety requirements and fire safety standards during installation work, the pipeline cavity is sealed with various sealing devices.
The most widely used in gas distribution systems low pressure the so-called "clay plugs" are fireclay clay packed in elastic cloth bags and rammed into the cavity of the pipeline. The length of the plug depends on the nature of the terrain, the quality of the clay, the time of year, the diameter of the pipeline, etc., but must be at least two pipe diameters and guarantee the safety of manual hot work. The stuffing and tamping of the clay cork is usually done by hand. To seal the cavity of the pipeline, in addition to clay plugs, the creation of which is a very laborious and inefficient operation, other methods are also used, the principle of operation of which is based on the introduction of various balls, plugs, scrapers and other mechanical separators into the pipeline, used when replacing sections of oil pipelines in a planned manner.
In the event of an oil or gas leak, there is a high probability of further development of damage, cracks, negative development of the accident, which can lead to an unacceptable cessation of pumping through the damaged section of the pipeline, and therefore the issue of reducing the time of shutting off the damaged pipeline and building a temporary bypass line is very relevant.
Cutting holes with a tubular end mill must be carried out at low speed so that the cutter teeth do not overheat, jam or break, and therefore on this technological stage there is no reserve for reducing the time of emergency pipeline repair.
Thus, only by reducing the installation time of a temporary bypass line, it is possible to reduce the total time for localization and elimination of an emergency without stopping the pumping that occurred on the pipeline.
It is also necessary to try to improve the first technological stage - emergency shutdown of the damaged section of the pipeline with the possibility of further repair work in the usual mode.
It is necessary to develop technical means and technology for quickly eliminating the accident and restoring pumping by the trenchless method of the "pipe in pipe" type, as well as without stopping the pumping of the transported product.
Study existing ways repair of underground pipelines revealed that quite well developed and successfully used for the repair of pipelines are technologies that provide for the opening and repair of defective sections with stopping pumping. But these technologies are quite expensive and not possible in all cases.
If it is necessary to repair pipelines in cramped conditions when finding places of damage under swamps, highways and other obstacles, the most effective are repair methods of the "pipe in pipe" type.
The use of "cold tie-in" with the simultaneous construction of a bypass line does not solve the issue of reducing the time for restoring a damaged pipeline, preventing the occurrence emergencies associated with the termination of the supply of energy resources to the objects of the industrial and social sphere of human activity, which are of a continuous nature.
Solving the problems of improving the accuracy and efficiency of methods for determining leaks, the formation of constrictions and blockages, creating effective and fast technologies for repairing pipelines using the “pipe in pipe” method, as well as without stopping pumping, would significantly reduce the repair time, loss of transported hydrocarbons, reduce pollution environment, which is very important.
During the current repair, defects noticed during operation are eliminated. Pipelines that coke or corrode during operation in process plants must be inspected and cleaned.
The scope of repair work includes:
inspection and repair of all supports and suspensions;
elimination of leakage in flange connections, tightening of flanges, change of gaskets;
checking the position of compensators;
checking valve seals;
checking the tightness of fittings;
replacement of worn pipelines.
Pipelines to be repaired must be completely emptied of the product.
Leaks in existing pipelines are determined visually, by drips, smell or a change in the pumping mode. Leaks along the pipe body or in welds can be eliminated by applying clamps that are made according to the shape of the pipe. Installed in such a way that when tightened, the gasket (asbestos, rubber, lead, fluoroplastic will hurt) remains sandwiched between the pipe and the clamp and fills the leaks. The clamp must have sufficient strength and rigidity for greater strength, the clamp is welded to the pipe. The material of the gaskets depends on the operating conditions of the pipeline. The gasket must not be dissolved or destroyed by the medium during long-term operation under working conditions. Ordinary rubber can be used at temperatures not exceeding 50 degrees. In pipelines for steam, gas, oil products, hot water and other liquids, at pressures up to 40 at. and temperatures up to 400 degrees, paranite gaskets are installed.
The accident caused by the rupture of the weld is eliminated by removing the defective area with subsequent welding. If the area is large - it is replaced. To do this, the pipeline is freed from the product and a section equal to at least one pipe diameter is cut out. Instead, a piece of pipe is welded.
Pipeline testing.
Upon completion of installation, and periodically after repair, pipelines pass hydraulic strength and density test , then washed and purged, and additionally tested for tightness with air or inert gas.
To do this, the pipeline at both ends will be plugged with welded plugs with air release valves, all installed fittings should be fully opened, mounting coils should be installed in place of control valves and measuring devices, and instrumentation fittings should be plugged. Testing with thermal and anti-corrosion insulation is allowed.
The pipeline is filled with water with a temperature of 5-40 degrees, but so as not to cause sweating. If the temperature is below 0, then measures against freezing are taken.
The piston pump creates the necessary pressure of crimping 1.25-1.5 from the working one, but not less than 2 atm.
Pressure oil pipelines must be subjected to a hydraulic test at a test pressure that is one and a half times the working pressure.
When filling with water, completely expel all air.
Increase pressure slowly. The rate of pressure rise must be specified in the project documentation. Do not use compressed air or gas to raise the pressure.
Disconnect the pipeline from the pump.
Withstand 10 minutes (strength test) and check: no drips, bulging and gusts.
The pressure must be controlled by two pressure gauges, accuracy class not lower than 1.5, with a diameter of at least 160 mm and a scale of 4/3 of the measured one. One is installed near the unit, the other at a remote point.
After that, the pressure is reduced to the working one and a thorough inspection of the welds is carried out (density test). During the inspection, tapping with a hammer weighing no more than 1.5 kg is allowed. During the pneumatic test, tapping is not allowed.
At the end of the inspection, the pressure is again increased to the test pressure and maintained for another 5 minutes, after which it is again reduced to the working one and the pipeline is carefully inspected again.
The duration of the tightness test is determined by the time of inspection and checking the tightness of detachable connections.
Then the air vents are opened and the pipeline is emptied through the drains.
The results are satisfactory if there are no breaks, visible deformations, pressure drop on the pressure gauge, no leaks and fogging. Undercutting of welded seams is prohibited.
If the results are unsatisfactory, the defects are eliminated, and the tests are repeated. The results are documented in an act or entered in the pipeline passport.
Substitution allowed hydraulic test to pneumatic in cases:
if the supports are not designed for the weight of water;
at T below 0 and danger of freezing;
if fluid is not allowed.
Subject to control testing by the method of acoustic emission and positive air temperature.
Pneumatic strength and density test produced by air or inert gas. Raise the pressure smoothly at a rate of 5% of R pr per minute, but not more than 2 atm per minute with periodic inspection of the pipeline at pressures up to 2 atm twice, more than 2 - 3. during the inspection, stop the pressure rise.
Leaks are identified by sound and soap emulsion.
For the duration of the tests, mark with flags a security zone of 10 m for underground laying and 25 m for above-ground, in both directions, and set up posts after 200 m. During the rise in pressure, the presence of people in the security zone is prohibited.
Compressors and pressure gauges should be located outside the security zone.
After the end of the hydraulic test, the pipeline is emptied and purged with air until the water is completely removed. Then, additional pneumatic tightness test air or inert gas under operating pressure for 24 hours new and at least 4 hours repaired.
The rate of pressure drop after holding to equalize the temperature is determined. The temperature is controlled by thermometers at different ends of the pipeline.
The pressure drop must be at least 0.2% per hour.