Compressed air pipeline test. Pneumatic testing of pipelines

Pneumatic test pipelines carried out to test them for strength and density or only for density. In the latter case, the pipeline must be pre-tested for strength. hydraulically. Ammonia and freon pipelines are not tested for hydraulic strength.

Pneumatic testing is supposed to be carried out with air or inert gas, for which mobile compressors or a factory compressed air network are used.

In exceptional cases, arising from the requirements of the project, it is allowed to carry out a pneumatic strength test of pipelines with a deviation from the data given in the table. In this case, the test must be carried out in strict accordance with a specially developed (for each case) instruction that ensures proper work safety.

Pneumatic strength test elevated cast-iron, as well as faolitic and glass pipelines is prohibited. In the case of installation of cast iron fittings on steel pipelines (except for ductile iron fittings), a pneumatic strength test is allowed at a pressure not exceeding 4 kgf / cm 2, while all cast iron fittings must pass a preliminary hydraulic strength test in accordance with GOST.

The pressure in the tested pipeline should be raised gradually, inspecting it when it reaches: 0.6 of the test pressure for pipelines with a working pressure of up to 2 kgf / cm 2; 0.3 and 0.6 of the test pressure for pipelines with a working pressure above 2 kgf / cm 2.

When inspecting the pipeline, an increase in pressure is not allowed. The final inspection is carried out at operating pressure and combined with a pipeline tightness test. At the same time, the tightness of welded joints, flange joints and glands is checked by coating them with a soapy or other solution.

Tapping a pipeline under pressure with a hammer is not allowed.

The results of the pneumatic test are considered satisfactory if during the strength test there was no pressure drop on the pressure gauge and during the subsequent tightness test, no leaks or gaps were found in the welds, flange joints and glands.

Pipelines transporting potent toxic substances and other products with toxic properties, liquefied petroleum gases, flammable and active gases, as well as flammable and combustible liquids transported at temperatures above their boiling point, subjected to further testing for density.

In this case, the test is carried out with the determination of the pressure drop. Shop pipelines transporting the products listed above undergo additional density tests together with the equipment to which they are connected.

The density test with the determination of the pressure drop can only be carried out after the temperatures inside the pipeline have equalized, for which thermometers should be installed at the beginning and end of the test section. Test duration intershop pipelines on the density with the determination of the pressure drop is set by the project; it must be at least 12 hours.

The pressure drop in the pipeline during its density test is determined by the formula:

DYA=10O / Rkon X Rnach

where DYa value of pressure drop, %;

Rcon and Rnach the sum of gauge and barometric pressures, respectively, at the end and beginning of the test, kgf/cm 2 ;

Tcon and Tnach are the absolute temperature of air or gas, respectively, at the end and beginning of the test, deg.

The pressure and temperature of air or gas in the pipeline is determined as the arithmetic average of the readings of all pressure gauges and thermometers installed on the pipeline.

An intershop pipeline with a conditional passage of 250 mm is recognized as having passed additional test on the. density, if the pressure drop in it for 1 hour as a percentage of the test pressure is not more than: 0.1 when transporting toxic products; 0.2 when transporting explosive, flammable, combustible and active gases (including liquefied ones).

When testing pipelines of other diameters, the fall rates in them are determined by multiplying the above figures by a correction factor.

For the duration of pneumatic tests, both indoors and outdoors, it is necessary to establish a protected area and mark it with flags. Minimum distance in any direction from the pipeline under test to the boundary of the zone: at overhead laying 25 m, and with underground 10 m.

Control posts are set up to monitor the protected area. During the rise in pressure in the pipeline and when testing it for strength, it is not allowed for people to stay in the protected area, except for persons specially designated for this purpose and instructed. An act is drawn up for the results of pneumatic tests of the pipeline.

To conduct a pneumatic test, pressure inside gas pipelines, oil and oil product pipelines is created with air or natural gas. Mobile devices are used as sources of compressed air. compressor units, which, depending on the volume of the cavity of the test area and the magnitude of the test pressure, are used one at a time or combined into groups. The time of filling the pipeline with air can be determined by the nomogram of the recommended app. 1. Natural gas for testing pipelines should be supplied from a well (only for field pipelines) or from existing gas pipelines crossing the facility under construction or passing directly near it. The pressure during the pneumatic strength test of the pipeline as a whole is last step should be equal to 1.1 R slave, and the duration of holding under this pressure is 12 hours. The graph of pressure changes in the pipeline during a pneumatic test is shown in Fig. 11. Filling the pipeline with air or natural gas is carried out with an inspection of the route at a pressure equal to 0.3 of the strength test, but not higher than 2 MPa (20 kgf / cm 2). An odorant should be added to natural gas or air during injection, which makes it easier to later find leaks in the pipeline. To do this, it is necessary to install installations for dosing odorant at the connection points to gas or air sources. The recommended rate of odorization with ethyl mercaptan is 50-80 g per 1000 m 3 of gas or air. If a leak is detected during inspection of the route or in the process of raising pressure, then the supply of air or gas to the pipeline should be immediately stopped, after which the possibility and expediency of further testing or the need to bypass air or gas to the adjacent section should be established.

Rice. 11. Graph of pressure changes in the pipeline during pneumatic testing:

1 - pressure rise; 2 - inspection of the pipeline; 3 - test of endurance; 4 - pressure release; 5 - tightness test.

Inspection of the route with an increase in pressure from 0.3 R use before R use and the passage of the strength test time is prohibited. After the end of the pipeline strength test, the phenomenon must be reduced to the design working level and only after that a control inspection of the route should be performed to check for tightness. Air or gas should, if possible, be bypassed to adjacent areas when depressurized. Considering that during pneumatic testing, the processes of filling the pipeline with natural gas and air up to the test pressure take a significant time, it is necessary Special attention turn to rational use energy accumulated in the pipeline by repeated bypass and pumping natural gas or air and tested areas to areas to be tested. To prevent loss of gas or air during ruptures, filling the pipeline with a pressure medium and raising the pressure to the test pressure must be carried out through bypass lines with closed line valves.

Page 2

Pneumatic tests are more responsible than hydraulic tests and aim to test the pipeline for tightness or strength. The pressure in the pipeline is created by filling it with compressed air or an inert gas, most often nitrogen. To carry out the test, mobile devices are connected to the pipeline. air compressors or other sources of compressed air or compressed gas. The supply of compressed gas is carried out in accordance with the requirements for temporary pipelines under pressure.

Pneumatic strength testing of pipelines located in existing workshops, as well as on overpasses, in channels and tunnels next to existing pipelines, is not allowed.

Pneumatic tests for the strength and tightness of the connection are carried out by pressure testing with air on a special stand. It is advisable to test a series of flanges simultaneously.

Pneumatic tests are explosive and therefore carried out in separate rooms or in fenced areas of the workshop. The air ducts are supplied with safety valves and verified pressure gauges.

Pneumatic test is different heightened danger, which increases when natural gas is used for testing. Then, in addition to the destruction of the pipeline, explosions and fires are possible. The destruction of the pipeline during pneumatic testing occurs with the ejection of soil and metal over considerable distances.

The pneumatic test is carried out with compressed air at the working pressure of the vessel. The density of the seams is checked by smearing them with a soapy solution or immersing them in water, if the dimensions of the vessel allow this. Bubbles form in places of leaks. For safety reasons, a pneumatic test is performed only after a preliminary hydraulic test of the vessel.

Pneumatic testing is carried out twice: preliminary - with powdering of pipes and final - after backfilling of trenches. Pipelines from cast iron pipes can be tested pneumatically if operating pressure in them does not exceed 0 5 MPa (5 kgf / cm2); with a higher working pressure, only a preliminary test is performed pneumatically, and a final test is carried out with water.

Pneumatic testing is carried out twice: preliminary - with powdering of pipes and final - after backfilling of trenches. Pipelines made of cast iron pipes can be tested by pneumatic methods if the working pressure in them does not exceed 0 5 MPa (5 kgf / cm2); with a higher working pressure, only a preliminary test is performed pneumatically, and a final test is carried out with water.

The pneumatic test shall be carried out with air or an inert gas and only during daylight hours.

Pneumatic testing is carried out according to several schemes, depending on the air or gas source used. Sources of natural gas for testing gas pipelines can be: gas fields; operating gas pipelines, to which the pipeline under construction is connected - branch; an existing gas pipeline crossing a pipeline under construction or passing in close proximity to it.

Pneumatic tightness test after tightening the flanges, which is accompanied by washing of welded and brazed seams, flanged joints of vessels, apparatus and pipelines.

The pneumatic test is carried out with air or, even better, with nitrogen at a pressure equal to the working one, but not less than 1 atm. After filling the system with gas, the specified pressure is maintained for 15 - 30 minutes. During this time, the temperature of the pipeline wall and the gas temperature equalize. If, after 1 hour after turning off the gas, the pressure in the system drops by no more than 1%, then the system can be considered tight.

The pneumatic test is carried out with air or an inert gas. At the same time, a pressure equal to 1 25 of the maximum working pressure is maintained, but not less than 0 2 MPa for steel pipelines.

ENiR

§ E9-2-9. Pipeline testing

Characteristics of the conditions for the production of work

Pipelines are tested hydraulically or pneumatically.
Pipelines are tested for strength and tightness, as a rule, in a hydraulic way. Depending on the climatic conditions in the construction area and in the absence of water, a pneumatic test method can be used for pipelines with an internal design pressure Pр, not more than: underground cast iron, asbestos-cement and reinforced concrete - 0.5 MPa (5 kgf / cm2); underground steel - 1.6 MPa (16 kgf / cm2); elevated steel - 0.3 MPa (3 kgf / cm2).
Trial pressure pipelines of all classes is carried out, as a rule, in two stages:
the first - a preliminary test for strength and tightness is carried out after backfilling of the sinuses with soil tamping to half the vertical diameter and powdering of pipes in accordance with the requirements of SNiP III-8-76 "Earthworks" with butt joints left open for inspection, but before closing the channels and installation of stuffing box compensators, sectional valves, hydrants, air vents, safety valves;
the second - the acceptance (final) test for strength and tightness is carried out after the pipeline is completely backfilled and construction and installation work is completed, all heating network equipment (gate valves, compensators, etc.) valves, instead of which flange plugs are installed for the duration of the test.
Preliminary testing of pipelines available for inspection in working order or subject to immediate backfilling during the construction process (performance of works in winter time, in cramped conditions) with appropriate justification in the projects, it is allowed not to produce.
Non-pressure pipelines are tested for tightness twice: preliminary before backfilling and acceptance (final) after backfilling.
The assembled gas pipeline is tested for strength and density with air after the installation of the shut-off valves.

Scope of work

During pneumatic testing of pipelines

1. Cleaning and purging of pipelines.
2. Installation of plugs and pressure gauge.
3. Accession to the pipeline of the compressor or a cylinder with air.
4. Filling the pipeline with air up to the specified pressure.
5. Preparation of a soap solution. 6. Inspection of the pipeline with lubrication of the joints with soapy water and a mark of defective places.
7. Elimination of detected defects.
8. Secondary testing and delivery of the pipeline.
9. Disconnect the compressor or cylinder and bleed the air from the pipeline.
10. Removing plugs and pressure gauge.

At hydraulic test pipelines

1. Cleaning of pipelines.
2. Installation of plugs with fixing them with temporary stops, pressure gauge and taps.
3. Connection of water supply and press.
4. Filling the pipeline with water up to the specified pressure.
5. Inspection of the pipeline with a mark of defective places.
6. Elimination of detected defects.
7. Secondary testing and delivery of the pipeline.
8. Disconnecting the water supply and draining the water from the pipeline.
9. Removal of plugs, stops and pressure gauges.

When flushing pipelines

1. Water connection.
2. Filling the pipeline with water.
3. Flushing of the pipeline until the water is completely purified from turbid impurities.
4. Draining water from the pipeline.
5. Filling the pipeline with chlorine water.
6. Draining chlorine water from the pipeline.
7. Secondary filling and flushing of the pipeline after chlorination.

Table 1

table 2

Norms of time and prices for 1 m of pipeline

Notes: 1. Table. 2 provides for the testing of steel, cast iron and asbestos-cement pipelines in sections up to 500 m, and ceramic, concrete and reinforced concrete sections up to 100 m. When testing steel, cast iron and asbestos-cement pipelines in sections of St. 500 m, and ceramic, concrete and reinforced concrete sections of St. 100 m Multiply time limits and rates by 0.75 (PR-1).
2. When testing pipelines by various links of workers for preliminary testing, multiply the Time Rates and Prices by 0.6 (PR-2), for the final test by 0.4 (PR-3).
3. During hydraulic testing of pipelines from hand press Multiply time limits and rates by 1.2 (PR-4).
4. The laying of a temporary water pipeline should be normalized according to § E9-1-2, table 2, note 1.
5. When flushing pipelines without chlorination, multiply the Time Rates and Prices of columns "e": for double filling of the pipeline - by 0.6 (PR-5), for a single filling - by 0.4 (PR-6).

There are two main types of testing of laid pipelines - preliminary and final.

Pressure pipelines are tested for strength and density (water tightness) hydraulically or pneumatically. The choice of method depends on the specific test conditions - climatic conditions, the availability of water for testing and the possibility of its discharge. In plumbing construction, the hydraulic method of testing pipelines is more often used.

Pressure pipelines laid in trenches or impassable tunnels and channels are tested twice. First, a preliminary test (for strength) is performed - before backfilling the trench and installing reinforcement, and then their final test (for density) - after backfilling the trench and completing all work on the test site.

Tests of pressure pipelines are carried out before the installation of hydrants, air vents, safety valves, instead of which flange plugs are installed for the duration of the tests (both stages).

A preliminary test for strength and tightness (first stage) is carried out after filling the sinuses with soil tamping to half the vertical diameter and powdering each pipe in the middle 0.5 ... insulation for welded joints.

The second stage - acceptance (final) test for strength and tightness is performed after the pipeline is completely backfilled.

It is recommended that all pipelines, except for plastic ones, be tested with a section length of at least 1 km. A long section is allowed, but the value of the allowable flow of pumped water should be determined as for a section 1 km long.

Pipelines made of HDPE, HDPE and PVC, regardless of the test method, should be tested in sections no longer than 0.5 km at a time.

The value of the test pressure is equal to the value of the internal design pressure plus the value of the additional pressure, taken depending on the upper limit of pressure measurement, the material and type of butt joint and the accuracy class and division value of the pressure gauge scale, according to SNiP.

The filling of the tested pipeline must be carried out with a certain intensity (m 3 / h) depending on the diameter of the pipeline.

The acceptance hydraulic test of the pressure pipeline begins after the trench with the seal is backfilled with soil. Then the pipeline is filled with water and kept filled, depending on the material of the pipes.

During the strength test, the pressure in the pressure pipeline is increased to the test pressure and maintained by pumping, then the pressure is reduced to the design internal pressure and maintained by pumping for the time required for inspection and detection of defects. If defects are found, they are eliminated and the pipeline is retested.

After a preliminary test, the backfilling of the pipeline is carried out, then they proceed to the tightness test. In this case, the pressure rises to the test one and the set time is maintained, if the pressure does not fall below the internal calculated one, then the pressure drop monitoring ends. If the pressure drops below the internal calculated value, then further testing is terminated and the defects are eliminated.

The pressure pipeline is recognized as having passed the preliminary and acceptance hydraulic leak test if the flow rate of the pumped water does not exceed the allowable flow rate given in SNiP. If the flow rate of the pumped water exceeds the allowable one, then defects are detected, they are eliminated, and the test is repeated.

89. Hydraulic testing of non-pressure pipelines. Testing and acceptance of non-pressure pipelines. Non-pressure gravity pipelines (sewer, storm) are tested only for density (tightness), and twice: before backfilling (preliminary) and after backfilling (final test). They are tested by filling with water in sections between adjacent wells, and they are filled from the upper well, and if the well is not tested, then through a riser, hermetically connected to the pipeline in the upper well. The filled section of the pipeline is kept for a day. The identified defects are eliminated, after which the pipeline is filled with water to the original level and the test begins, i.e., measurement of water leakage. Hydrostatic pressure in the pipeline during the leakage test is created by filling the upper well or the riser installed in it with water , and the value of this pressure at the top of the pipeline is determined by the magnitude of the excess of the water level in the well or riser above the pipe line or above the horizon ground water, if the latter is located above the shelyga. The value of the hydrostatic pressure must not be less than the depth of the pipes, counting to the top of the well in the upper "well of each tested section. When pre-testing non-pressure pipelines for density, they are inspected, during which, to maintain pressure in the pipeline, water is pumped into the riser or well. Pipeline is considered to have passed the preliminary test if no visible water leaks are found during its inspection.The final test of pipelines consists in determining the water leak and comparing it with the permissible (normative).The amount of leakage is determined in the upper well by the volume of water added to the well or riser to the initial level, creating the necessary hydrostatic pressure.This test should last at least 30 minutes, and the decrease in the water level in the well or riser is allowed no more than 20 cm. blunt water in the lower well in a volumetric way or with the help of a weir.

90 Ways to develop underwater trenches. The development of underwater trenches is carried out mechanically or hydraulically using rope-scraper installations, hydraulic monitors and suction dredgers, and in the presence of rocky soils, using an explosive method. Development of underwater trenches by rope-scraper installations, consisting of a scraper bucket, head and tail bearings with blocks, a set of ropes and a scraper winch, can be carried out in almost all soils, including loosened rock. The width of the trench depends on the width of the scraper buckets and ranges from 1.3 to 2.2 m. Winches are used to move the scraper bucket in an underwater trench. In recent years, rope-scraper installations of one- and two-way action (both strokes are working) with a bucket with a capacity of up to 7 m 3 and a winch with a pulling force of up to 1000 kN have been created. Self-discharging scraper buckets with an opening bottom have also been created, which speeds up the emptying of the buckets from the ground. Underwater trenching hydraulic monitors is the simplest and most economical, since there is no need to lift and transport the soil. For large volumes of work, jet projectiles are used, the water to the jet nozzle of which is supplied from centrifugal pump with a supply of up to 1000 m 3 / h at a pressure of up to 200 m. The projectile's telescopic tube allows excavation at a depth of up to 20 m. pumping units low power (50 ... 100 m 3 / h) with the development of soil under water by divers. Underwater excavation with suction dredgers most effective when constructing underwater trenches in non-cohesive soils of small size (sands, fine gravel). The depth of soil excavation from the water surface by modern dredgers reaches 40 ... 50 m, and the productivity is 2500 m 3 / h . Development of underwater trenches in rocky soils often carried out with the help of explosions with overhead or blast-hole charges, and the work is carried out in two stages: crushing the rock and cleaning the rocky soil. But explosions under water lead to the death of "fish, therefore, in recent times, the development of rocky soils is more often performed using special rock-crushing shells, which are a vessel with a well (mine), in which a chisel weighing up to 20 tons is placed in the guide holder, with which the rock is crushed .

91. Ways of laying siphons in underwater trenches.Pulling pipelines throughbottom used for laying pipelines of large diameters. Laying is carried out in the following sequence: installation of the pipeline with applying insulation, lining, equipping it with ballast weights and pontoons; track device; laying the pipeline on it; arrangement of coastal supports and installation of a system of blocks for pulling the pipeline; laying a traction cable along the bottom of the trench; pulling the pipeline with a winch or tractor. The descent path is arranged in the form of a narrow-gauge rail 750 mm wide with a slope towards the river. The pipeline is lowered along the rail track on trolleys, which at the end of the track roll into a specially arranged pit, from where they are removed by a crane or diverted along a bypass track. The pipeline with plugs at the ends is rolled into the water and transported afloat to the place of laying. By way of free diving is carried out in the following sequence: launching the pipeline into the water; towing to the place of laying; installation in the crossing section; lowering it to the bottom of the trench. The pipeline, covered with insulation and with plugs welded at the ends, is lowered from the shore or from slipways into the water. Further, the lashes of the pipeline are towed by the alloy method using boats. After installing and fixing the pipeline, water is pumped into it exactly at the crossing point and immersed to the bottom of the trench. From floating supports used for a significant length of underwater pipelines laid at great depths, when the methods of dragging and free diving are not applicable. The assembled pipeline, after its isolation and installation of plugs, is moved from the onshore slipway and installed afloat parallel to the shore above the siphon alignment. Then the floating supports are brought to the pipeline, dispersing them at the calculated distances from each other, and the pipeline is fixed with the help of towel slings and ropes to the lifting devices of these floating supports. Floating platforms are also brought to the pipeline and fixed, which serve to hold the pipeline in alignment. After that, the pipeline with floating platforms and supports is brought afloat into the alignment of the siphon with the help of tug boats. During the laying process, the pipeline is filled with water and held on the lifting devices of the floating supports, and then the ropes of the supports are evenly released (pitted), ensuring a gradual immersion of the pipeline to the bottom of the trench. Sequential extension method used for laying underwater pipelines through wide water barriers. The extension of the whip is produced in two ways: in the surface position and underwater. In the first case, the whips are built up on pontoons or specially equipped ships that serve as an assembly site. On them, whips are assembled and welded from pipe sections prepared in advance, insulated and ballasted on the shore. In a submerged position, the build-up is carried out by connecting sections laid on the bottom by divers, most often on flanges. To prevent the ascent of siphons, they are loaded with loads, most often reinforced concrete in the form of half-couplings or saddle-shaped loads. Ice pack carried out in various ways. In winter, pipelines are laid from ice using supports and free immersion. For laying pipelines along the alignment of the siphon in ice circular saws cut a through hole (manna). The prepared pipeline is laid over the lane on linings (beds) laid across the hole. Then they install supports (goats) with hoists, with the help of which it is lowered to the bottom. With the method of free immersion of the pipeline with filling with water, it is lowered without the use of supports and hoists. The advantage of laying siphons from ice is the convenience of work, since floating equipment is not required, the delivery of pipe strings to the installation site is greatly facilitated, which generally reduces the cost and speeds up work.

92 Laying pipelines through dry ravines. Complicated by the need to work in conditions of steep slopes. At the same time, depending on their steepness, various methods of pipe installation are used, including “top-down”, “bottom-up” and a combined method. Installation "from the bottom up" is carried out with the delivery of pipe sections to the slope by pipe-laying cranes (Fig. a), tractors or winches installed on the top of the slope (Fig. b). With a slope of up to 20 ° and good soil condition, pipes or sections are delivered to the installation site by tractors and built up sequentially. Docking is carried out using one or two pipelayers. When mounted with a winch, the length of the sections can be significant. Installation of the siphon pipeline using the “top-down” method can be carried out on any slopes, but it is more advisable for steep slopes (Fig. c). At the same time, the assembly and welding of pipes or their sections are carried out without machines and mechanisms working on the slopes. The first section is lowered into the trench with one or two pipe-laying cranes and fastened with cables to the tractors. below and above. The tractor pulls the stackable pipeline down, and the other keeps it from spontaneous slipping when joining each subsequent section. After docking at the top of the next section, the pipeline is pulled down to the length of this section (Fig. d). In order to avoid damage to the insulating coating of the pipeline, a lining is made of wooden slats over the insulation. Siphons through small ravines are mounted from one or more elements, which are isolated, lined, laid in the design position and then connected to the pipeline.

1 - laid pipeline; 2 - docked pipe section; 3 - anchor cable; 4 - delivered section; 5 - traction cable; 6 - winch; 7 - trench; 8, 9, 10, - pipelayers; eleven - insulated pipe; 12 - clamping grip; 13 - mounting platform; 14 - stackable string of the pipeline; 15 - sled; 16 - plug; Tr 1 Tr 2 - tractors

93 Cable-stayed and beam crossings of elevated pipelines. During installation cable-stayed crossings available for floating facilities, for the installation of pipelines, sites are arranged along the crossing line within the water table at the minimum possible distance from each other (Fig. c). Bearing and wind ropes are dragged with the help of a temporary traction rope and a winch in a taut state so that they do not come into contact with water, after which they are raised to the pylons. Installation, welding and hydraulic testing of the prepared pipeline section is carried out at the installation site located at the crossing on the shore. The finished whip is pulled through with a winch or tractor and a hauling rope. Depending on the length of the span and the height of the coast, the whip is dragged along the floating supports or along the supporting saddles of the span.

13 - carrying cable; 14 - rollers; 13 - dragged section of the pipeline; 16 - roller support; 17 - pontoon with roller support; 18 - rope to winch

Beam transitions are mounted at the bottom of the stage: first, supports are installed, and then the pipeline is mounted overhead or lifted. If the span exceeds 10 m, intermediate supports are installed (Fig. a). With the method of sliding the pipeline strings on rollers, winches (traction and brake) are pulled onto the supports. When installing single-span beam transitions from one section or lash with an accessible transition for machines, assembly, welding and hydraulic testing of the lash are carried out at the bottom of the obstacle. If it is necessary to mount a multi-span passage under such conditions, then the lashes are delivered directly to its supports and then placed by cranes in the design position (Fig. a). If the passage is not available for machines, the whips are delivered to the installation site by water and then mounted by floating cranes. The simplest single-span beam crossings through water obstacles are mounted by dragging (Fig. b), followed by lifting and laying by cranes on supports (Fig. c).

/ - laid pipeline; 2 - anchor; 3 - mounting joint; 4, 5 - supports (temporary and permanent); 6 - mounting elements; 7 - braces; 8 - electric welding unit; 9 - dragged pipeline section; 10 - cap with bracket; // - cable to the tractor or winch; 12 - the laid section of the pipeline;

94 Arched and hanging pipes of overhead pipelines. Arched pipeline transitions are mounted from enlarged blocks - semi-arches (Fig. d). Installation begins with the installation of shore stops with nests left and concreted metal support frames. Then, on special stands, mounting elements (semi-arches) are prepared for lifting. When crossing railway tracks, the arched passage is mounted by railway cranes using a mobile temporary mounting support (Fig. e).

/ - laid pipeline; 4, 5 - supports (temporary and permanent); 6 - mounting elements; 13 - truck crane or pipelayer; 14 - coupling with a thrust bearing; 15 - traverse; 16 - stretch marks; 11 - support with a jack; 18 - railway platform with mounting support; 19 - bandages for closing the arch; 20 - railway crane; 21 - crawler crane; 22 - area for pre-assembly of sections; M1-2, M-3, M4-5, M6-7-6 - mounting elements of the arched transition

hanging.Installation of pipes on pylons is carried out by lifting or overlaying. With both methods, pylons and massive reinforced concrete anchors are first installed. with straps attached to them. Then risers are mounted with compensation loops of the pipeline. Further, between the pylons on floats or temporary supports, lay out the lash of the pipeline. When installing the pipeline by lifting, the whip is lifted to the design position by synchronously operating chain hoists on both pylons, after which it is connected to the suspension units and the main conduit. When installing by sliding (Fig. b) a temporary mounting cable is pulled between the pylons on the blocks, and a traction cable is attached to the pipeline laid at one of the pylons and rollers are attached to the pipeline every 14 ... 15 m on rigid racks. Both cables are thrown over blocks at the tops of the pylons and attached to a tractor on the opposite bank. Then, with two or four pipe-laying cranes, the prepared pipe string is lifted and fed so that it moves to the opposite pylon, leaning on the mounting cable with rollers. The whips give the design deflection, attach it to the veneer hangers and weld it into one thread with the pipeline sections on both sides of the transition.

1

- pylons; 2 - chain hoists; 3 - working rope with suspensions; 4 - outlet blocks; 5 - anchor; 6 - permanent supports; 7 - winch with chain hoists; 8 - overhead pipeline; 9 - temporary support; 10 - blocks (rollers) on hangers through 12...14 m; 11, 12 - traction and mounting cables;