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When assembling transportation networks for various purposes, for example, heating communications or pipelines intended for the distillation of oil and gas, until recently, ordinary pipes made of steel were mainly used. For the most part, products of this type still cope well with their work. However, such pipes still have one rather serious drawback. Whatever the thickness of their walls, they cannot protect the distilled liquid from the cold in winter.
The result of freezing of water or coolant in the lines is usually the failure of the latter. At the same time, in the municipal steel networks during the cold season, among other things, significant heat losses are also observed, which makes their operation much more expensive.
What are PPU pipes
To prevent freezing of liquids transported along highways, the latter, when assembling the network on the street, are either laid very deep underground, or additionally insulated using special materials. Both methods are labor-intensive and technologically complex. Therefore, recently, pipes of a special design - pre-insulated - have become increasingly popular.
Products of this type are insulated even at the production stage using a modern insulator with a very low degree of thermal conductivity - polyurethane foam. These pipes are more expensive than conventional ones. However, the highways assembled from them can serve in the future without the need for repairs for decades.
Design of PPU pipes
Outwardly, such products are very similar to the well-known sandwich chimneys. That is, they consist of three main layers:
the steel pipe itself, through which liquid will be pumped in the future;
a layer of polyurethane foam;
outer protective shell.
Special signal cables pass through the polyurethane foam layer in such pipes. Thanks to their presence, it is always possible with high precision determine the location of the accident on the highway and quickly carry out repair work.
What technical characteristics can have
Today, pre-insulated pipes are supplied to the market in a wide range. Such products may differ in:
diameter
wall thickness;
thickness of the insulating layer;
the number of signal cables laid, etc.
The cost of products of this variety directly depends on their diameter and the thickness of the insulating layer. According to the latter indicator, PPU pipes are selected taking into account the climate of the region in which the network is supposed to be assembled, as well as the depth of the latter. In warm areas, pipelines are usually assembled with a thickness of an insulating layer of 5 cm. In the northern regions, pipes with an insulating layer of 10 cm or more are used.
Two or three signal cables can be laid in the insulating layer of such products, depending on the diameter.
GOST standards
Pre-insulated pipes are produced in our country with strict observance of GOST requirements. The insulation used in the manufacture of such products, in any case, must meet the following requirements:
water absorption by volume - 10%;
compressive elasticity - not less than 0.3 MPa (deformation in all directions - up to 10%);
density - up to 60 kg / m 3.
When heated to 110 ° C, the length of the PPU insulator used in the assembly of pipes should not exceed 3%.
Polyurethane foam for pipe insulation can be made using different technologies. But most often such material is made on the basis of carbon dioxide and freon. In most cases, in the manufacture of PPU pipes, polyurethane foam of such well-established brands as Dow, Izolan, Huntsman, Elostokam is used.
Types by design
There are currently two main types of pre-insulated pipes on the market:
Products of the first variety are made of ordinary or galvanized steel with polyurethane foam insulation. Outside, such pipes are sheathed with sheets of hard steel or stainless steel.
Flexible products of this type are made using a similar technology. However, such pipes are not covered with a sheath of steel, but of corrugated plastic. Of course, such products do not differ in too much flexibility. After all, polyurethane foam - the material itself is quite rigid and not too elastic. However, it is still possible to slightly bend the pipes of this variety during installation.
Of course, in the manufacture of plastic shells of pre-insulated pipes, GOSTs are also observed without fail. Used for their assembly is usually the highest quality light-stabilized material.
Sometimes protective sheaths with an insulating layer can be supplied separately from the pipes themselves. In this case, before their installation during assembly, they are preliminarily checked for leaks, and then coated with an anti-corrosion compound.
How is an insulating layer applied to a PPU pipe?
Many domestic factories produce such products. Pre-insulated pipes are also supplied to the Russian market, of course, by foreign companies.
Judging by the reviews, the quality of domestic products of this type today at a lower cost is practically in no way inferior to imported ones. For example, simply excellent reviews from consumers have earned such products manufactured by the Novosibirsk Preinsulated Pipe Plant, Orlovsky Pipe Insulation Plant, the Stroyizolatsiya plant (Seversk), etc.
In any case, in the manufacture of such products, specialists without fail, among other things, make sure that the adhesion between the polyurethane foam and the steel pipe is as strong as possible. To prevent the insulation from slipping on steel and holding it as securely as possible, before applying it, the base is carefully cleaned to form a rough surface while removing rust.
When foaming the polyurethane foam itself, the specified thermal regime must be maintained exactly. It is also possible to improve adhesion between the inner shell with foam filler by treating the latter with a discharge.
So that the insulator that has not yet solidified does not flow out, a special metal plug is attached to the end of the pipe. After the material has hardened, this element is removed from the pre-insulated PPU pipe. Such products go on sale with an uncovered end of the polyurethane foam layer.
Scope of use
The most widespread PPU pipes at the moment are, of course, primarily in industry. Such products are used during assembly mainly:
oil pipelines;
gas pipelines;
steam pipelines.
Very often, pre-insulated pipes are also used for heating networks intended for pumping heated liquids. Such communications are usually mounted in hot shops of enterprises of various specializations.
Recently, pre-insulated pipes have begun to gain immense popularity among public utilities. Organizations of such specialization use these products when laying centralized heating systems and water pipelines of cities and towns. The use of such pipes in this case significantly improve the quality of public service.
Main advantages
Pre-insulated pipes for heating mains, water pipelines, oil pipelines, etc., or rather, for assembly, are used in our country, therefore, quite often. But what explains such popularity of modern products of this type?
The undoubted advantages of PPU pipes, in comparison with conventional ones, include:
the ability to install any communications in the shortest possible time and with minimal labor costs;
reduction of heat loss (usually from 40% to 2%);
a significant increase in the efficiency of pipelines;
increasing the service life of networks by 2-5 times;
reducing the cost of repairing pipelines.
Due to the presence of a protective shell, such lines are practically not afraid of exposure to aggressive environments. It is allowed to lay PPU pipelines without grounding and preliminary drainage arrangement. Polyurethane foam differs, among other things, in that it does not allow moisture to pass through. Consequently, steel pipes insulated using this material are much less prone to rust.
Flaws
There are practically no minuses for PPU pipes. Perhaps the only drawback of such products is their rather high cost. However, this minus is more than offset by the long service life of the PPU mains and the lack of the need for their frequent repairs.
Mounting Features
PPU pipes are made, therefore, from high-quality steel. Consequently, their installation is carried out using welding. Of course, the laying of pre-insulated pipes during the assembly of various kinds of industrial and utility networks is carried out using a special technology. Polyurethane foam is a material that, unfortunately, does not tolerate too much high temperatures. Therefore, when welding such pipes, special protective screens are mandatory.
After connecting the segments, the craftsmen who assemble the PPU line must check the quality of the seams made. After the metal has completely cooled at the joints, special couplings are applied to the pipes, among other things. A feature of such structural elements of PPU-lines is that they are made of heat-shrinkable material. After cooling, such a coupling decreases in size and tightly fits the weld, thereby ensuring complete tightness. When using docking elements of this type, a small cavity remains at the joints of the pipes, into which mounting foam or polyurethane foam is subsequently poured.
The technology described above is used both in the assembly of large industrial highways and small household engineering communication networks.
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Pre-insulated heating mains: what are the advantages?
Pre-insulated pipes are a special type of product that is used when laying large heating mains and heating systems. Unique features of such products are given not only by materials, but also by the presence of a technical control system, which is not used for pipes of other types.
Pipe scheme
1 - pressure corrugated pipe stainless steel; 2 - conductors-indicators (when producing pipes with the ODK system); 3 - thermal insulation made of polyurethane foam;
4 - corrugated protective sheath made of polyethylene.
When laying such routes, heat losses are reduced significantly, they amount to a value of up to 2%, which was previously considered impossible even when using heaters. Pre-insulated pipes are already fully finished products that do not require additional work during installation, which significantly reduces all costs for installation and further maintenance.
Feature of pre-insulated pipelines
The pre-insulated pipeline is a special system that is designed for laying heating mains. Such pipes have numerous advantages and features, the main thing being that the pipe consists of several layers, each of which has its own characteristics.
So, part of the pipes, which is intended for underground laying, is made of steel and a polyurethane sheath, between which a heat-insulating layer is laid, but for pipes of the above-ground system, the outer sheath is made of galvanization, which effectively protects the route from corrosion, adverse weather conditions, and other influences. .
Production specifics
Pre-insulated steel products are intended for laying heating mains, while pipelines in a steel or polyethylene sheath are laid in a channelless underground way, and in galvanized - in through channels or tunnels above the ground.
The pipes themselves are a “sandwich” structure, consisting of the following layers: a pressure steel inner pipe, a special signal wire SODK (technical control), a heat-insulating layer (usually made of foamed polyurethane), a protective sheath. It turns out a special pipe, consisting of two separate pipes with thermal insulation, which is located between them.
It is the features of production that ensure the resistance of pipes to corrosion, which is very important for the constituent elements of any heating main.
Before the start of insulation, the pipe undergoes special treatment in a shot blasting machine. This gives the surface a slight roughness, which improves the adhesion of the thermal insulation layer to the core of the inner tube.
The polyethylene sheath is also subjected to a corona treatment on its inside, which guarantees excellent adhesion between the insulation and the pipe. All pipes pre-treated in this way acquire their own unique properties allowing them to be used in the most adverse conditions.
Technical quality control
Today, insulated pipes are offered, which can have sheaths made of various materials. Most often, these are shells made of polyethylene and galvanized steel, which may be suitable for laying underground and aboveground routes.
A casing made of such materials provides protection against any mechanical damage, moisture, and corrosion. In addition, the diffusion of polyurethane, which is the main material for the production of the pipe itself, is prevented.
Solder pipe connections.
Most often, high-density polyethylene is used for the manufacture of an insulating sheath, which is considered the most effective for underground laying. Polyethylene itself is thermally and light-stabilized, its color is black, it is produced strictly in accordance with GOST 16330, but in some cases GOST 18599 can be used.
It is used for insulation and polyurethane foam, which is excellent for steel pipes.
All pre-insulated pipes are subject to mandatory technical control, which allows us to guarantee the quality of the product. During laboratory tests, such characteristics of the pipe are determined as:
- density;
- compressive strength at 10 percent strain;
- volume fraction of all closed pores;
- water absorption during boiling;
- shear strength;
- thermal conductivity.
Welded joints are 100% tested using modern method ultrasonic testing, which is a mandatory requirement before implementation.
Benefits of using
Scheme of assembly of parts of a pre-insulated flexible piping system.
All pre-insulated steel products differ from others for laying heating mains by the following advantages:
- The on-line remote control system makes it possible to significantly increase the strength and reliability of such pipes, and to reduce all the costs of repairing the laid heating mains.
- The service life is about 30 years, while simple uninsulated pipelines last only 10-15 years. This reduces the cost of replacing unusable pipes, maintenance of the route, and repairs.
- Such a pipe reduces heat loss during use to 2%, although when laying uninsulated pipelines, such losses are quite significant - from 25%.
- Steel insulated tracks are laid much easier and faster than usual, construction time is reduced by about two to three times, since there is no need to arrange channels and wells, and this causes a reduction in all costs.
- All steel pipes do not require additional anti-corrosion coating, as they already have all the necessary properties. This allows you to reduce the cost of laying many times over.
- The heat resistance of pipes is up to 150 degrees.
We can draw the following conclusions: all pre-insulated pipelines are much more profitable for the installation of heating mains, since they are more modern and less expensive. Their durability is twice as long, and maintenance and repair costs are reduced by the same amount. In a word, this is a profitable and promising option.
Materials of the pre-insulated pipeline of the heating network
For the construction of heating networks, pre-insulated pipes and parts are used
according to manufacturer's catalogues.
The material of the steel pipe must comply with the requirements of the Design Rules and
safe operation of steam pipelines and hot water approved
Ministry of Emergency Situations and Ministry of Labor of the Republic of Belarus
(3.1.1 and 3.1.2).
Changing the direction of the pipeline route of the heating network is carried out using
pre-insulated bends with an angle of 15, 30, 45, 60, 75, 90° factory-made.
Route turns at an angle of 15 ° or less are carried out by trimming individual
sections of the pipeline at an angle of not more than 5 °.
Fittings - preinsulated Ball Valves(valves).
Compensation for temperature elongation of pipelines is carried out due to
applications L, Z, U-systems, disposable compensators, preheating
pipeline during installation.
The connection of steel pipelines of different diameters is carried out by welding with
using standard transitions.
Connection of joints of external polyethylene pipes is carried out using
a special sheath to be put on the pipeline, made of low-density polyethylene
pressure grades 273-79, 273-80, 273-81 according to GOST 16338 or polyethylene high pressure
Sealing of butt joints is carried out using heat shrink tape
or heat shrink bandage.
For thermal insulation of butt joints, polyurethane foam PPU-317M (TU
6355-55-221-1472), consisting of component A 317M / 1 according to TU 6.55.221.14.71 and component B
(polyisocyanate) according to TU 113.03.38-106.
5.10
To perform thermal and hydraulic insulation at the ends of the pipeline
a special end nozzle, polyurethane foam components are used, as well as
heat shrink tape or sleeve.
Transportation and storage of pre-insulated elements
During transportation, loading and unloading of pre-insulated pipes and their elements
precautions must be taken not to damage the outer
polyethylene pipe-shell.
Loading and unloading operations must be carried out using soft
wide slings and slings with end grips. Cannot be used as steel slings
cables, cords, etc., causing deformation of the surface of polyethylene pipes. Throw
pipes are prohibited.
Transportation of pipes by road and loading and unloading operations
allowed at outdoor air temperature up to minus 20 °C. Pipes should be stored in
stacks on a flat platform, equipped with beds, located in 2 m increments.
The height of the stack should not exceed 1 m. The stacks should be placed under a canopy,
protecting pipes from impact sun rays and atmospheric precipitation.
The duration of storage of pre-insulated products should be specified by their
manufacturer.
5.15
Liquid components of polyurethane foam should be stored in heated rooms
at temperatures from 15 to 30 °C.
Earthworks and auxiliary works
Excavation, auxiliary and preparatory work should be carried out in accordance with
the requirements of SNB 5.01.01 and SNiP 3.05.03.
The depth of the trench is determined by the project according to the longitudinal profile on the basis
permissible depths of laying pipelines, taking into account leveling sand bedding
not less than 100 mm thick. The density of the backfilled soil after compaction should
be in the range from 1700 to 1800 kg/m"
The minimum width of the bottom of the trench depends on the size of the corresponding
pipe diameters and regulated horizontal distances between pipes and the wall
trenches. The distance from the pipe to the trench wall must be at least 100 mm. Distance
between pipes, mm, is accepted for pipes with a diameter of:
from 250 to 780 mm - 250;
more than 900 mm - 350.
In the places where the connections of pre-insulated elements are made, the trench must be
expand and deepen, based on the convenience of performing work.
The bottom must be flat and sloped in accordance with the design.
The tolerance for bottom unevenness should not exceed 3 cm over a length of 1 m.
6.1
Heating network from pre-insulated pipes are mounted in compliance with the requirements
supervision by representatives of the design organization and the customer. The work must be carried out under favorable weather conditions. Welding of pipes should be performed at a temperature not lower than 0 °C, and insulation and sealing of joints should be performed at a temperature not lower than 10 °C. In case of precipitation, the sealing of the joints must be carried out under cover (a tent made of film, tarpaulin, etc.).
Pipeline laying
6.2 The pre-insulated pipeline should be laid on a leveling layer of sandat least 10 cm thick.
Lowering into the trench of pre-insulated pipes with an outer diameter of up to 160 mm is allowed to be carried out manually or using a winch (crane). When doing so, care must be taken not to damage the jacket pipe.
Pre-insulated pipes containing detection alarm devices
faults in the insulation of the pipeline, must be laid so that the control
the wires were at the top of the pipe.
The pipeline should be laid with a slope of at least 2% 0 .
6.5 Welding of joints and branches of pre-insulated pipelines is carried out
directly in the trench. In some cases, it is allowed to weld the pipeline over
trench, which is stipulated by the project.
In this case, pre-insulated pipes must be laid on wooden linings with a section of 100x100 mm, which are placed in steps of 2 to 3 m.
Before laying pre-insulated pipes and elements in a trench, it is necessary to
pipes to put on temporary plugs.
All connections of steel pipes and their elements should be made by electric welding.
Gas welding is allowed for pipes with a diameter of up to 50 mm.
Welding work when connecting pre-insulated pipes should be carried out in accordance with
requirements of current regulations.
During gas welding it is necessary to use protective screens to protect the insulation and the jacket pipe from the action of the burner flame.
Before starting welding, the ends of steel pipes must be thoroughly cleaned of
anti-corrosion oil with active degreasers, without solvents, as well as
from polyurethane foam, because when it burns, toxic gases are released.
After making welded joints and testing pipelines for tightness
proceed to the implementation of the device alarm system.
If you want to shorten a pre-insulated pipe, you must
the following operations:
measure the given segment and mark the place of the cut;
measure from the cut point on the remaining pipe 200 mm and mark with a circular line;
so as not to damage the signal wires;
Remove the cut section of the polyethylene sheath pipe;
remove the polyurethane foam insulation in the area of removal of the jacket pipe using
knife or other cutting tools, being careful not to damage the wires
alarms;
Thoroughly clean the surface of the steel pipe to prevent
incineration of polyurethane foam residues that emit toxic gases;
Installation of butt joints
6.13
Wooden linings are laid on a sandy base, the distance between
which should be no more than 3.0 m. The alignment of the welded pipes is ensured.
Before starting the connection, a coupling is put on one of the ends of the pipe. If a
heat shrink rings are used, then you need to put them on as well.
After checking the alignment, the pipes are welded.
If pipes with signal wires are installed, it is necessary that the wires are at the top in the position "10 minutes to 14 hours".
When installing the transition, two couplings of different diameters are required, which are first put on the ends of the pipes to be welded. When installing a heat shrink seal, the following steps must be taken:
complete, if necessary, the installation of an alarm;
run the signal wires through the heat shrink seal, and if there is
the need is to connect the signal wires to each other;
clean the steel pipe with a metal brush from rust;
clean the outer polyethylene pipe from foreign objects and clean it;
heat steel and polyethylene pipes up to 60 °С;
After checking the coupling for tightness, components are poured into the coupling hole
polyurethane foam. After the foam has hardened, the hole is sealed with a cork.
Alarm system
6.14
To monitor the condition (humidification) of the heat-insulating layer of the pipeline
an alarm system is installed.
The system consists of two copper wires (hereinafter - wires) with a cross-sectional area of 1.5 mm 2, mounted in polyurethane foam insulation at a distance of 15 to 20 mm from the steel pipe in the "10 minutes to 14 hours" position.
Installation of butt joints
Sealing the end of the pipeline
6.26 Before sealing the end of the pipeline, it is necessary to close the opening of the steel pipe.
After positive test results for tightness at the end of the pipeline
put on the end sleeve so that between the bottom of the sleeve and the end of the steel pipe
thermal insulation thickness was 5 cm for pipes up to 200 mm in diameter and 7.5 cm for pipes
with a diameter of more than 250 mm.
For hydraulic isolation of the end of the pre-insulated pipeline, heat-shrink sleeves are used.
Backfilling of pipelines with soil
6.27 Backfilling starts with sandfilling.
Sand sprinkling should be done in two layers. The first layer is to fill the space between the pipelines, as well as between the pipeline and the trench wall, and then compact the layer. Lay the second layer horizontally, at least 10 cm above the pipeline and seal.
After the sand filling is completed, fill the remaining part of the trench with the soil previously selected from the trench (removing large stones and hard blocks from it) and compact it mechanically.
Special Requirements
In the case of laying pre-insulated pipelines in places subject to
dynamic loads (exceeding 5.0 t/axle), as well as with a covering layer less than
50 cm, in the places provided by the project, at a height of at least 30 cm above the surface
pipeline must be laid reinforced concrete slab, or lay the pipeline in
protective pipes or reinforced concrete channels.
Mark the heating network with a warning tape laid at a distance of 30 cm
above the pipeline.
7.1 Testing and flushing of heat pipelines is carried out in accordance with the requirements
SNiP 3.05.03 and "Rules for the design and safe operation of pipelines for steam and
hot water", ed. 1994
Heat pipelines must be subjected to preliminary and final tests for strength and tightness.
Preliminary testing of pipelines should be carried out in separate sections as installation and welding work is completed before the installation of start-up equipment, bellows expansion joints, shutoff valves, but after the welded section of the heat pipeline is laid and the ends of the test section are welded with plugs. The use of shut-off valves to disconnect the test section is not allowed.
Acts are drawn up on the results of testing and washing.
Acceptance of pipelines into operation must be carried out in accordance with
the requirements of SNB 1.03.04, taking into account the instructions of SNiP 3.05.03.
The customer and the general contractor represent acceptance committee, Besides
stipulated by SNiP 3.05.03 documents, additionally:
passports of manufacturing plants for equipment and certificates for pipelines;
acts on the stretching of expansion joints and pre-heating of sections
heat pipelines;
7.5 The operating organization must necessarily store information about the sections of the heating network laid with preheating of heat pipelines.
8 Safety requirements for the production of work
When performing work, it is necessary to comply with the requirements of SNiP Sh-4-80*.
To work on the installation of heat networks from pipes with thermal insulation from
polyurethane foam in a polyethylene sheath allowed persons over 18 years old,
passed a medical examination, special training, introductory briefing
and on-the-job safety training.
8.3 In case of fire of the thermal insulation of pipes, fittings, parts and elements,
use conventional fire extinguishing media; in the event of a fire in an enclosed space,
use BKF brand gas masks.
When drying or welding the ends of steel pipes free from thermal insulation, the ends of the thermal insulation should be protected with detachable tin screens with a thickness of 0.8 to 1 mm to prevent ignition from a propane burner flame, arc welding sparks.
When heat shrinking polyethylene sleeves and cuffs with a propane burner flame
it is necessary to monitor the heating of couplings, cuffs and polyethylene pipe sheaths, do not
allowing polyethylene to burn or ignite.
Waste polyurethane foam and polyethylene when cutting insulated pipes and
release of steel pipes from insulation should be immediately after the end of the working
operations are assembled and stored in a specially designated place on the construction site on
distance of at least 2 meters from heat-insulated pipes and parts.
Thermal insulation of pipes and parts (foamed polyurethane foam and polyethylene) does not
explosive, under normal conditions does not emit in environment toxic substances
and does not have a direct contact with a harmful effect on the human body. Handling it does not require special precautions (hazard class 4 according to GOST 12.1.007).
(preparation of a mixture of polyurethane foam, pouring the mixture into a joint) should be carried out using special protective equipment (cotton suit, safety shoes,
rubber gloves, cotton mittens, goggles).
When filling with polyurethane foam the joints of pipelines laid in through channels (tunnels), it is necessary to use a RU-60M type respirator.
8.8 At the place where the joints are filled with polyurethane foam, there should be means for degassing the substances used (10% ammonia solution, 5% hydrochloric acid solution), as well as a first-aid kit with medicines (1.3% saline solution, 5% boric acid, 2% solution of baking soda, iodine solution, bandage, cotton wool, tourniquet). It must be remembered that component "B" of the mixture of polyurethane foam (polyisocyanate) refers to toxic substances.
9 Environmental protection
When laying heating networks, the requirements of SNiP 3.05.03 for
environmental protection.
It is not allowed without obtaining permission in accordance with the established procedure to produce
work on the construction of a heating network.
Flushing of pipelines should be carried out with the reuse of water.
Drainage of water from pipelines after washing (disinfection) should be carried out in places
provided by the PPR.
The territory after completion of work on the installation of a heating network should be
cleared of waste from construction and installation works and restored in accordance with
project requirements.
Waste insulation from polyurethane foam and polyethylene should be collected for
their subsequent removal to the plant for disposal or disposal in permitted places.
The use of pre-insulated pipelines with an insulation control system device makes it possible to stop the process of damage to pipelines from external corrosion. Moreover, the undoubted advantages of pre-insulated pipelines are to ensure less heat loss due to polyurethane foam insulation, in comparison with conventional channel laying, heat losses are reduced by about 3-3 .8 times.
The laying of pre-insulated pipelines, in addition, has significant advantages compared to the traditional one, it does not require the use of reinforced concrete products and structures, has a significantly lower pipeline laying depth and reduces construction time by 3-4 times.
Finished pre-insulated pipelines and fittings are manufactured by SKTB "Sarmat" in accordance with TU RB 14739482.130-97.
Pre-insulated pipes and parts are made of steel pipe with a thermal insulation coating of industrial polyurethane foam (CFC-free and ozone-resistant) with a waterproof coating of polyethylene or galvanized sheet.
The insulation is made of rigid polyurethane foam. The thermal conductivity coefficient is not more than 0.033 W\mK.
The total density is 80 kg \ m 3.
The resistance to compression is not less than 0.3Mpa.
Shear resistance - (0.15-0.4) MPa.
The shell pipe is made of polyethylene. The thermal conductivity coefficient is not more than 0.43 W\mK.
Density-950kg\m.
Service life-50 years.
Polyethylene pipes made without a seam are resistant to impact, corrosion, and also to the action of ultraviolet rays. For air laying, there is a sheath made of galvanized sheet in the form of a spirally coiled pipe TU RB 00012262-166-9.
Pre-insulated pipelines are used in heating networks both for channelless underground laying and for above-ground laying. In the practice of building heating networks, pipelines with polyurethane foam thermal insulation of the "pipe in pipe" type (PPU pipes) are used. The pipeline consists of a pipe, polyurethane foam insulation and a protective sheath (Fig. 3). Steel or polymer (for hot water supply) pipes are used. Polyethylene centering supports are installed between the pipe and the casing.
Pre-insulated piping provides the following advantages over existing structures:
Increased durability (pipeline resource) by 2-3 times;
Reduction of heat losses by 2-3 times;
Reducing operating costs by 9 times (specific damage is reduced by 10 times);
Reducing capital costs in construction by 1.3 times;
Availability of a system of operational remote control over the dampening of thermal insulation.
Pre-insulated pipes have been successfully used for the construction of:
Heating networks;
Hot water supply systems;
Technological pipelines;
Oil pipelines.
Thermal insulation is applied to the entire length of steel pipes and fittings, with the exception of end sections equal to 150 mm for pipes with a diameter of up to 219 mm, and 210 mm for pipes with a diameter of 273 mm or more. The joints are thermally insulated at the construction site, after welding and testing of the pipeline. Insulation of pipe sections with welded joints can be carried out according to one of the methods: installation of insulating shells made of rigid polyurethane foam with the application of a waterproofing material; installation of polyethylene couplings with polyurethane foam filling into the cavity of the coupling.
Protective shells are made in the form thin-walled pipes made of high density polyethylene. They are intended for pipelines directly located in the ground, providing their water tightness and mechanical protection.
For pipelines located above the ground, a protective sheath made of galvanized steel with a zinc coating thickness of at least 70 microns is used.
Pipelines made of steel pipes are equipped with an on-line remote control system for wetting insulation, consisting of two copper wires (one of which is electrically insulated, and the second without insulation) and an electronic signaling unit. When the insulation becomes wet due to corrosion of the pipe or violation of the integrity of the containment, the ohmic resistance of the system changes, which is recorded by the alarm unit.
The service life of the thermal insulation of pipes and fittings must be at least 25 years. Polyurethane foam does not have a harmful effect on the environment and ensures high-quality operation of the insulation at temperatures up to 130 °C.
Very often, when creating water supply systems or transporting various kinds of industrial liquids, the question of protecting pipelines arises.
They need to be protected from mechanical damage, atmospheric influences, but first of all, protection is needed from the effects of cold. Be that as it may, it is the too low temperature on the street that most seriously affects the condition of the pipes, as well as their carrier.
Thermally insulated pipes perform their functions at any air temperature, which distinguishes them from ordinary ones. Realizing the popularity of thermal insulation of pipelines, the developers decided to go further and created the so-called pre-insulated samples.
What is it and what are they? We will enlighten you on this matter.
Article content
What is the difference between simple pipes?
An ordinary pipe for transporting a certain kind of substance, what is it? Most likely, a steel or plastic elongated segment of a hollow cylinder is called a pipe.
The pipe can have walls of different thicknesses, a certain diameter, and can even bend. The walls are both very thin, for domestic use, and quite thick, up to 10-15 mm or even more.
In the latter case, we are talking about high pressure lines mounted on industrial enterprises, where it is necessary to be able to distill carriers under enormous pressure and temperature through communication systems.
No matter how thick the wall of the pipe is, it still cannot protect its insides from freezing. Metal conducts heat very well, as does plastic, although the latter has a slightly lower thermal conductivity.
At zero temperature, a pipe without protection can still function properly, but at -10 it can no longer. The carrier will either freeze completely or begin to slowly deposit on the walls. Sooner or later, all this will affect the functioning of the system, completely blocking it.
That's why it's so necessary. Without it, any pipeline laid along the street will simply freeze during the winter. An exception will not be the system of warm water supply or heating.
Even if the heating pipe does not freeze due to the conflict of high and low temperatures there will be a discrepancy in the temperature of the carrier at the inlet and outlet of the line.
The carrier will lose a rather impressive part of the thermal energy free of charge, which is also not very good. After all, the efficiency decreases, and resources for its artificial increase will have to be spent many times more.
Alternative option
Protecting heating or water pipes is easy enough. You just need to think over the system of their thermal insulation. The materials are used from the same line as the raw materials for insulating the load-bearing structures of the house.
Most often used:
- mineral wool;
- expanded polystyrene;
- penoizol;
- foam polyethylene.
Each option is good in its own way. But all of them, one way or another, involve additional processing of the pipe, which takes time and money. This process can be simplified.
Unlike the load-bearing structures of the house, which, by the way, have also recently been produced pre-insulated, pipes are very easy to pre-process.
After all, all samples are unified, manufacturers know which models to focus on and what exactly the buyer needs, and therefore they act in key areas.
This is how pre-insulated pipes appeared - that is, those that were treated with thermal insulation at the production stage at the factory.
Technology and design
Most often, pre-insulated pipes are produced large sizes. This is due to the fact that household pipelines are laid mainly inside buildings or underground.
That is, they do not have access to air, which means that there is no danger of freezing. If, however, some section is nevertheless laid on the surface, then due to the small length, it will not be difficult for the owner to isolate it.
While in industry they try to keep all pipeline lines on the surface in order to have access to any of their sections if necessary.
This, in turn, creates the need for high-quality protection of pipes from low temperatures, which automatically increases the demand for industrial pre-insulated pipes.
Their design is very simple. In fact, we have an ordinary pipe with a coaxial sheath. That is, the outer shell is mounted on the inner, solid body of the pipe. They are mounted when the axes coincide, that is, the axes do not intersect and are kept parallel to each other.
The gap between the pipe body and its protective sheath is filled with a heat insulator. At the very beginning they used different materials, now preference is given to penoizol.
So it turns out that heat-insulated products are analogues of conventional ones, only in a two-layer protective casing. Its first layer functions directly as thermal insulation, and the second as additional mechanical protection.
As an outer shell use:
- tin steel;
- plastic (including corrugated).
Penoizol properties
Manufacturers of pre-insulated pipes chose Penoizol for a reason. He has mass useful properties but at the same time it also has disadvantages.
Of the useful properties are:
- Low thermal conductivity.
- High strength.
- Efficiency.
- Low weight.
- Vapor permeability.
- Zero reaction to moisture.
- No corrosion.
- Durability.
Great stuff, isn't it? It has all the properties that are necessary for high-quality insulation. The problem here is only that penoizol is applied in the form of finished foam.
The process is very similar to applying polyurethane foam, only on a much larger scale.
And this, frankly, is not always convenient. Normal interaction will require expensive equipment, ingredients for mixing the composition, as well as some experience, since penoizol tends to shrink, and unevenly, depending on many factors.
For independent use, and even on pipes, this option is unacceptable. The result will be shapeless, unaesthetic, and the process itself will take a lot of time.
Another thing is processing at the factory, where all stages are automated and calculated to the second. Here, pipes pre-insulated with penoizol have become a real breakthrough.
They are easy to produce (you just need to assemble a coaxial base and fill the gap between the shell and the protective casing), they are extremely effective and quite cheap (the price drops due to unification and acceleration of production).
At the exit, pipes are obtained with perhaps the best, additional mechanical protection and good cost.
Note that pipes insulated without penoizol can also be found on the market. For example, foamed, flexible models with a shell filled with foamed polyethylene, etc.
But they are almost always inferior to the above-described samples in all respects, including economic ones, and therefore they have not found such popularity.
Types of pre-insulated pipes
There are two main types of pre-insulated pipes. There are pipes:
- hard;
- flexible.
Rigid pipes are standard. There is an inner section of a pipe of a certain diameter, treated with a layer of penoizol. The thickness of the layer depends on the tasks that are set for a particular system.
In cold regions, it can be 10 centimeters or more, and in warmer regions, insulation with a thickness of 5 cm is enough.
The outer protective layer is made of tin steel, in rare cases, stainless steel. Such products are perfect for assembling main water supply systems, pressure industrial pipelines, central wiring, etc.
Flexible variations are produced using a similar technology, only instead of an outer shell of metal, a corrugated plastic frame is made. It cannot be called exceptionally flexible, and penoizol inside is not so easy to bend, but still some degree of freedom is allowed.
The segment can be laid along a small radius, if desired, bent and twisted the way you want. Even if the insulation inside is damaged, you will not feel any significant consequences on the functioning of the water supply system.
Connection of pre-insulated pipes (video)
Additional Variations
Pre-insulated pipes are produced mainly single and monolithic. But this is not always the case. For narrower tasks, models with combined wiring are also produced.
That is, they may have not one large segment inside the casing, but several. Of course, they are much thinner and not as effective, but they are well insulated and reinforced. Any damage or freezing of such a structure does not threaten.
The option with several small pipes is interesting in that it is possible to lay entire clusters of communications in this way, while forming a compact, aesthetic and extremely convenient system.
Its only drawback is the need to open the casing in the event of a breakthrough in one of the pipes. Moreover, it is not so easy to understand what exactly broke through and where.
Also, any self-respecting manufacturer of pre-insulated pipes is engaged in the manufacture of protected fittings that would fit their products. The most common options are quadruple wiring, corner fittings, locking elements, etc.
