Graphically, this is shown in Figure 4. Layered crystalline structures are connected through amorphous polymer segments, i.e. cross chains. The probability of the formation of cross chains increases with the length of the polymer chain.
Cross-chain molecules are known to increase the stiffness of a material and improve its flexural stress cracking resistance (ESCR) or long-term creep properties by "bonding" a plurality of crystals together. The side chains exhibit stretchability and mobility and as such can absorb and dissipate energy.
Figure 4: Cross-chain molecules increase compound stiffness
Cross-chain molecules increase ESCR and stiffness by "linking" multiple crystals
Cross chains are stretchable and mobile (can absorb/dissipate energy)
The type of introduced co-monomer also affects the concentration of cross chains. As the chain length of the α-olefin com-monomer increases, the cross-chaining ability also increases. Figure 5 shows that 1-octene is more efficient than the shorter α-olefins. The reason for this is that the side chains of octene are longer and therefore more difficult for them to incorporate into the growing crystal. This leads to a higher probability of cross chain formation at the same comonomer concentration.
Figure 5 : The type of comonomer affects the likelihood of forming cross-chain molecules
When designing a molecular structure, it is important to control the concentration of the comonomer and how it is incorporated into the polymer chain. Figure 6 shows a curve showing the relationship between molecular weight and the likelihood of cross-chain formation in ethylene-octene copolymers made using Dow's patented solution polymerization technology. By controlling the incorporation of co-monomer, different polymer morphologies can be obtained leading to a different balance of properties.
By applying these ideas, a new family of DOWLEX polyethylene compounds has been developed for the production of utility pipes.
Figure 6: Influence of Molecular Weight on the Probability of Formation of Cross-Chain Molecules
These developments form the basis for a new class of polyethylene materials for high temperature applications. These compounds are defined in the ISO-1043-1® standard as PE-RT or high temperature resistant polyethylene.
PE-RT exhibits excellent long-term hydrostatic strength without the need for crosslinking. This allows pipe manufacturers to gain significant processing advantages over cross-linked PEX. As defined in the ISO 10508 standard, PERT can be used in the production of any hot water pipes.
DOWLEX Polyethylenes have been successfully used in hot water pipe manufacturing for over 20 years, with more than 1,000,000 km of pipes already installed.
For potable water pipes, it is important to comply with national requirements for products intended to come into contact with water. These requirements include taste and odor characteristics, inhibition of microbial growth, and disclosure of material composition to ensure that all additives used in the production of that material are on the "positive list".
Due to good long-term hydrostatic strength at high temperatures, combined with excellent flexibility, DOWLEX 2344E and DOWLEX 2388 are the best solution for pipes for heating and water supply.
DOWLEX PE Pipe Compounds: Worldwide Certification
- Certified as non-crosslinked in the following countries: Austria, Australia, Canada, China, Czech Republic, France, Germany, Hungary, Iran, Netherlands, Poland, Russia, Slovakia, Slovenia, Spain, Switzerland, USA
- Approved for drinking water in Austria, Denmark, France, Germany, Italy, Netherlands, France, Russia, UK, USA.
Tubing made from DOWLEX 2344E exhibits excellent long-term hydrostatic strength at elevated temperatures without the need for crosslinking. This makes this product particularly suitable for the production of hot water pipes. Approvals for this material have been issued in a number of countries, for example DOWLEX 2344E complies with the German standard DIN 16833(6) (PE-RT) and the corresponding DIN 4721 application standard.: KIWA(8) approved for all hot water pipes in the Netherlands; and in the US, this material is listed on the PPI(9) list at 180°F (approx. 82°C). DOWLEX 2344E DOWLEX 2388 are the only non-crosslinkable polyethylenes in this class. Multilayer multilayer pipes meet the requirements of ASTM1282-01A00.
Pipes made from DOWLEX 2344E are extremely flexible, making them easy to install. It is possible to apply standard PE welding technologies without the need for crosslinking. In addition, the lack of crosslinking allows high production speeds to be achieved. This advantage is important for the production of multilayer composite pipes. The high smoothness of DOWLEX tubing results in reduced head loss and minimal fouling.
The newest member of the DOWLEX family of polyethylene pipe compounds is DOWLEX 2388, an ethylene-octene copolymer manufactured using Dow's patented solution polymerization technology. This product is designed to combine excellent long-term hydrostatic strength with excellent machinability.
Benefits of PE-RT for pipe production
- Line speed > 60 m/min. without technological additives
- No loss of raw materials during start-up of the equipment, since the material can be recycled
- Saving time + production costs:
- No additional vulcanization step required
- No laboratory analysis required to determine degree of crosslinking
- Good taste and smell characteristics
- Excellent weldability
Figure 7 DOWLEX 2388 Ring Voltage Characteristics, Scanning Electron Microscope according to ISO 9080
As can be seen from Figure 7, the regression curves of DOWLEX 2388 are very "sloping", which ensures high design stresses over a long period of time, especially at elevated temperatures. At a temperature of 110 °C, the failure time, which is much longer than one year, makes it possible to predict the service life of pipes at 70 °C over 50 years, at 60 °C about 100 years (using extrapolation indicators according to ISO 9080). The resulting design stress is not only comparable to cross-linked PEX, but exceeds it.
Plastic pipes for water supply - withstand temperatures from -70°C to 110°C (min and max temperature conditions are indicated), have a blue coating. For gas supply - has a yellow or orange color.
Production of PERT pipes
The HDPE pressure pipe is made of polyethylene and has a protective layer. Manufacturers use different coatings (protection) from modified additives, minerals, light and heat stabilized compositions based on propylene and polypropylene.
Connection methods
To connect pipes made of polyethylene with increased heat resistance, the same methods are used as for cross-linked PE:
- Sliding fittings. Installation is available to a specialist of any qualification. Mainly used for small diameter pipes.
- Crimp fittings. Polyethylene fills the entire docking space, so the connection is reliable and installation is quick.
- Electrofittings. The most reliable connection method.
- Flanges. It is used for pipes of large diameter and connection of sections of critical pipelines.
Connection of pe-rt pipes with pipes made of other material (PP, PA, PB, metal) transitional removable and non-removable couplings are used.
PERT pipe installation
Installation is carried out in several ways:
- Trench method, without the use of sand backfill.
- For laying are used incl. and gentle methods.
- Different types of drilling, for example, horizontal directional.
- Trenchless laying by the methods of punctures with a pneumatic punch.
- It is possible to lay in unstable soils using the plow-rotary laying method, as well as in other soils (rocky terrain, coarse-grained, excluding boulder, crushed stone, pebble-gravel).
- Rotary excavation - backfilling.
- Restoration in a trenchless way without dismantling the old one - relining.
- During the current repair of external systems - renovation.
PE-RT is a modern and versatile polymeric material, characterized by a large margin of safety and high resistance to temperature effects. Type 2 PE-RT pipes can be used for heating, cold and hot water supply. They are also widely used to protect power supply and communication cables. Compared with other types of polyethylene pipes, PE-RT type 2 products have the following advantages:
Widest operating temperature range. Permissible constant temperature of the heat carrier is 95°С. At the same time, flexibility is maintained at sub-zero temperatures, down to -50°C, which eliminates the formation of cracks during storage and transportation in winter. When water freezes inside, pipes are also not damaged; after defrosting, they retain their original shape.
Corrosion and chemical resistance. PE-RT pipes are not affected by hard water and can withstand acidic and alkaline environments. There are no deposits on the walls of polyethylene pipes that reduce the throughput.
Flexibility and elasticity. Pipes of small diameters are suitable for hidden wiring and allow concreting. PE-RT pipes with a diameter of up to 110 mm inclusive can be supplied in coils, which allows such a pipe to be laid using a trenchless method, as well as inside old metal pipelines without dismantling them.
High working pressure. For pipes with sufficient wall thickness, the nominal working pressure is 16 atmospheres at a medium temperature up to 95°C. Thin-walled pipes are designed for constant pressure up to 10 atmospheres.
Fast installation. The length of the segment in the bay allows you to do without intermediate connections. It also reduces the amount of waste.
Low thermal conductivity minimizes heat loss in heating networks.
Reliable connection. PE-RT pipes can be welded in the same way as any other polyethylene pipes - butt-welded or with electrofusion fittings.
Using PE-RT pipes for cable laying
Type II PE-RT pipes are often used for cable installation. In this case, both standard pipes and pipes specially designed for this purpose with an additional protective layer can be used.
Manufacturers offer several options for pipes designed for laying power, telecommunications and signal cables, as well as fiber optic lines. For example, the company "Tehstroy" produces a series of pipes TEHSTROY TR (temperature resistant) made of polyethylene with increased heat resistance. High resistance to temperature fluctuations allows laying a pipe at any depth, including above the depth of soil freezing. Operating temperature ranges from -20°C to +95°C.
The TEHSTROY TR series includes single-layer pipes with a nominal outer diameter Dn and pipes with an additional protective layer, sold under the brand name Techstroy TR-1 Prosafe. The protective sheath, made of thermoplastic polymer, may be red or green. Both types of pipes are produced in diameters from 16 to 630 mm, which allows you to choose the optimal size for both mains and single signal and communication lines.
The use of pipes with a protective layer makes it possible to lay pipelines directly into the ground, as well as along the bottom of reservoirs with or without penetration into the ground. The use of the HDD method often makes it possible to reduce laying costs, since it does not require excavation and greatly reduces the number of joints.
Pipe Thermotech Thermosystem®(old name Thermotech >MIDI< Composite) является модернизированным вариантом труб PE-RT, полностью изготовленной из материала Dowlex 2344 (тип 1) и 2388 (тип 2) (PE-RT, торговая марка Dowlex принадлежит концерну DOW Chemical Corp.) с большим числом связей между молекулами, с кислородным барьером (EVOH), спрятанным внутрь трубы между слоями полиэтилена. Т.к. все слои являются полимерами, то в результате последовательного соединения слоев образуется труба, как единое целое, стабильная в условиях колебания температуры и давления, с небольшим линейным удлинением, устойчивая к механическим воздействиям.
Let's decipher the abbreviation PE-RT - PolyEthylene of Raised Temperature resistance - polyethylene of increased heat resistance - the secret lies in the large number of carbon bonds in the molecules. The side chains of the linear Standard Polyethylene (PE) molecule are formed by a combination of butene molecules. Two carbon atoms are used to connect the main chains to each other, so the likelihood of entanglement is low. The side chains of the linear PE-RT polyethylene molecule increase the number of bonding carbon atoms to 6, while the degree of interlacing is much higher. If the original material for PEX - Polyethylene, with the same content of monomers, is not "cross-linked", then it will provide much lower strength under prolonged exposure to pressure.
Underfloor heating pipe Thermotech Thermosystem®- has an anti-diffusion layer OXYDEX (EVOH polyethylene), which prevents the penetration of oxygen and an anti-creak layer, which make up a single whole with the pipe.
Anti-diffusion layer OXYDEX: During the production of pipes, a thin layer of modified polyethylene, 0.1 mm thick, is applied to the surface of the “main” PE-RT pipe. This is followed by the same layer of EVOH plastic (ethyl vinyl hydroxide). Previously, this anti-diffusion layer was applied on the outside of the pipe. Over time, some manufacturers also used Thermotech pipes, incl. another one was applied to it - a protective layer of polyethylene.
The new polymer pipes from Thermotech - ThermoSystem pipes made of PE-RT type II polyethylene - are more flexible and more reliable compared to pipes of the old type ThermoSystem (12, 17 and 20 mm) due to the location of the anti-diffusion layer on the inner surface of the pipe with a protective layer polyethylene. The oxygen barrier is protected from mechanical damage by the entire thickness of the pipe wall
The EVOH layer acts as a diffusion barrier to oxygen and the polyethylene layer increases the bond between the pipe and the diffusion barrier. The barrier is firmly bonded to the pipe, allowing small radii bends without wrinkling. Oxygen-tight pipes thermotech complies with DIN 4726 (Deutsches Institut fur Normung), and is less than 0.1 g/m2. for 24 hours at 40 °C. OXYDEX layer in pipes thermotech reliably protected from mechanical damage by a protective layer of polyethylene. The melting point of the anti-diffusion layer is 180 ° C. These properties allow the use of such pipes at carrier operating temperatures up to 95 ° C, and in short-term modes up to 110 ° C, that is, mainly in hot water and heating systems, warm floors.
Oxygen entering the system does not cause any harm to the pipes themselves, it only reacts with the metal parts of the system, causing accelerated corrosion of heating boilers, pumps, radiators, valves and other metal equipment. This process is especially accelerated when pipes are used in systems with elevated temperatures, i.e. in heating systems (especially in radiators). Unfortunately, in SNiP there is no permissible value for oxygen penetration in systems made of plastic pipes. Therefore, in reality, pipes without a diffusion layer are often used, which already after 5 years leads to the failure of the steel elements of the system. In order to prevent this from happening, it is necessary to use only pipes in heating systems that meet the requirements of the German standard DIN 4726. It should be noted that today only a few companies can offer such pipes that would meet the requirements of this standard.
This pipe is capable of withstanding high pressures. The service life of PERT pipes is determined by nomograms depending on the temperature and pressure of the working medium (as well as all other polymer pipes). According to Russian certification, PE-RT pipes are classified as type "t" (heavy), i.e. withstanding pressure of 20 kgf/cm2.
Under the THERMOTECH brand, 5-layer non-reinforced pipes for heating and water supply systems are produced:
- thermotech Thermosystem PE-RT I diameters 8x1, 12x2 mm, 17x2 mm, 26x3 mm
- Thermotech MultiPipe PE-RT II diameters 16x2, 26x3,
- Thermotech Thermosystem PE-RT II diameter 20x2, 32x3 mm
Advantages of the Thermotech pipe
Thermotech = reliable + easy to install + inexpensive!
Extreme flexibility and strength without the use of a cross-linking agent. The secret lies in the large number of carbon bonds in the molecules. To understand the difference, answer the question: what kind of shoes do you prefer to buy - with a piping sewn to the sole (similar to the molecular crosslinking of polyethylene) or with a glued sole (similar to the chemical crosslinking of polyethylene or glued plastics)?
The service life of the pipe is over 50 years. It requires virtually no maintenance during operation, which further facilitates the work of utilities.
Capable of withstanding high pressures and temperatures. The service life of PERT pipes is determined by nomograms (see appendix) depending on the temperature and pressure of the working medium. According to Russian certification, PE-RT pipes are classified as type "t" (heavy), i.e. withstand pressure 20 kgf/cm2
Polyethylene pipes are 5-7 times lighter than steel pipes. Pipes are produced seamless in standard coils 12*2.0 mm (1000 m), 16*2.0 mm (750 m), 20*2.0 mm (650 m), 25*2.3 mm (350 m), 32 *3.0 mm (50 m). This significantly reduces transport costs and facilitates the work of installers.
The temperature linear expansion of PE-RT pipes is several times less than that of standard PEX pipes. With a temperature change of 50°C, the linear elongation of PE-RT pipes remains only 0.3%, and with a change of 90°C - 0.7%. When cooled, the pipe completely returns to its original shape.
Docking of polyethylene pipes is much cheaper, easier and takes less time. The pipes are connected using crimp brass fittings and takes seconds. The entire installer's tool consists of pruning shears and a wrench. Therefore, even a non-specialist can change or install plumbing for himself.
No creaking in underfloor water heating systems.
Due to the low surface roughness (0.125 microns), the pipes are not subject to overgrowth, therefore they practically do not need maintenance during operation and are silent at almost any flow rate.
Frost-resistant and able to withstand several cycles of freezing - thawing (for example, water).
It has high maintainability. Multiple docking and undocking of the fitting is allowed, while the pipe at the junction retains its properties.
They can be used for transporting foodstuffs, aggressive liquids and gases.
Fully meet the requirements of the modern industry, the aesthetics of the production of works and the operation of pipelines.
Warranty periods: storage period 3 years, service life 7 years.
The pipe is resistant to chemicals and mechanical wear.
Foreign certification.
The pipe has been tested in SKZ (Suddeutsches Kunststoff Zentrum). According to SKZ tests, the service life of the PERT pipe is 490 years with a safety factor of 2.5.
According to the TUV (Technisher Uberwaschungs - veren Bayern) conclusion, a pipe with an OXYDEX layer is not subject to oxygen diffusion (does not let air through).
The production has an international quality certificate ISO 9002.
Russian certification.
GOSSTROY OF RUSSIA No. 0130837*. Application in heating systems.
HYGIENIC CERTIFICATES. According to the test results at Polymertest LLC, the service life of the MIDI pipe is more than 100 years, depending on the operating conditions.
ROSTSTANDARD. Application in hot water, cold water systems.
Certified for heating systems with operating temperatures of the coolant up to 95 °, in peaks - up to 110 ° C (no worse than any other polymer pipes), pressure - up to 20 kgf / cm2 (!).
Pipes Thermotech Thermosystem® manufactured in Germany by the HPG concern by order of Thermotech (Sweden).
DEVELOPER and MANUFACTURER of PE-RT compound Dowlex 2344 - "The Dow Chemical Company"
Materials and articles "The Dow Chemical Company" in attachments:
- PE-RT, a new class of polyethylene for hot water pipes
- PE-RT, a new class of polyethylene for industrial pipes
How do pipes for underfloor heating behave at low temperatures? We do not object to the use of pipes in conditions with low temperatures. Moreover, well-known objects with PE-RT pipes have been operated for years on arenas with artificial ice in Europe without any problems.
PERT pipes retain high strength even at temperatures down to -40°C.
Compared to other polymers, DOWLEX 2344E has a higher thermal conductivity at negative temperatures (2-3 times higher), which means that the power of refrigeration units can be reduced.
In Thermotech pipes, the inner surface is mirrored, they have a very low roughness (0.125 microns, class 10), which is less than that of PEX pipes and significantly less than any metal-plastic pipes. The fact is that in metal-plastic pipes the main load is borne by the aluminum layer and therefore the polymer layers in such pipes are of poorer quality than in plastic pipes. Reducing hydraulic losses in Thermotech pipes will reduce the power of circulation pumps.
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Made a lot of things. For a very long time there were no competitive offers at all! There are no complaints.
Differences of pipes >>>
Many private houses are heated with underfloor heating systems. This factor is explained by the efficiency of this type of heating. The coolant circulating through a pipeline laid under the floor has a much lower temperature than in radiators. This means that much less energy is spent on heating it.
Warm floors do not spoil the interior of the premises at all, as they are hidden from the eyes of those around them with a finishing coating. And the air heated over the entire surface of the floor is always directed upwards, creating a favorable microclimate and increasing the level of comfort.
Ideally, the use of such heating systems should be provided for even at the stage of building a house. Otherwise, you will need to carry out calculations and large-scale work that requires certain skills and craftsmanship. In addition to choosing high-quality heating and pumping equipment, it is necessary to pay close attention to the choice of consumables, the main of which is a pipe.
It is a mistake to believe that any pipe can be laid in a concrete screed. Increased requirements are imposed on this element of the system, since the service life of the warm water floor and the quality of the entire system will depend on it.
And although this consumable is presented in a huge assortment on the construction market, not every one of them meets all the quality and safety requirements.
Which pipe is suitable for laying a water circuit and will not only extend its service life, but also save money? What do the designations PEX and PE-RT mean? What are the advantages of PERT polyethylene, which has recently appeared on the Russian market?
Requirements for pipes
In most cases, the contours of a water-heated floor are filled with a heavy concrete screed, closed with a finish. Even after removing the tile or removing part of the laminate, it will be impossible to visually inspect the system for leaks or any other malfunctions.
Therefore, any pipe that is part of underfloor heating water systems must meet stringent requirements stipulated by the special conditions of its operation.
The main element of water-heated floor systems has a standard diameter that can correspond to the following values:
It should be noted that when using a consumable material of a smaller diameter, heat transfer decreases, which leads to a reduction in the distance between the loops of the circuit and, accordingly, to an increase in the consumption of materials. In addition, the small diameter of the pipe leads to overloads of pumping equipment. It is not advisable to use pipes of too large diameter, as in this case the thickness of the concrete screed will increase and, as a result, the load on the floor.
Do-it-yourself water-heated floor
What materials are pipes for underfloor heating made of?
So what material should be preferred when arranging underfloor heating water systems? And here you should not be led by the assurances of sellers that all their goods meet the necessary requirements. Such indiscretion can lead to problems that arise already at the stage of installation of systems.
In the production of pipes for underfloor heating, several materials are used.
- Polypropylene. This option is the most budget. And this is perhaps his only positive quality. It will not work to mount a circuit from a single piece of pipe, since they are sold in small footage. This material is not characterized by high plasticity, therefore, laying the contour is possible only if a large step between the loops is observed. And most importantly, polypropylene has a very low heat transfer coefficient, so the system will be inefficient.
- Metal. Metal pipes can be made of copper and corrugated steel. These materials are of high quality and durability. But their significant drawback is the high cost, inaccessible to most of the population.
- Polyethylene (PEX and PE-RT). This includes metal-plastic. In the production of all varieties, different types of polyethylene are used, and each pipe has a special structure and is processed using various technologies. These materials are distinguished by ease of installation, resistance to mechanical and thermal stress, as well as affordable cost.
PEX pipes
First of all, it is necessary to understand what the concept of "cross-linked polyethylene" or PEX means. Many items used in everyday life are made of polyethylene. However, in its original form, this material is sensitive to high temperatures.
And everything is to blame for the structure of the material, the molecules of which are not interconnected in any way. This drawback is eliminated by applying a special processing of polyethylene, which allows the molecules to “crosslink”, due to which the polyethylene acquires stability and does not melt under the influence of high temperatures.
Pipes for underfloor heating
As a result of such processing, the PEX pipe acquires another positive quality, which consists in the ability to return to its original shape. That is, if during the operation of water-heated floor systems the pipe experiences overloads or is subject to mechanical action that changes its position, after reducing the load intensity, it will take the originally specified shape.
Crosslinking of polyethylene is carried out using different technologies, designated as follows:
It should be noted that when arranging water circuits, the PEX-a pipe is most often used. The next two varieties are used much less frequently due to their lower quality. And PEX-d pipes have not been used at all in recent years.
PE-RT pipes
The designation on the pipe "PE-RT" means that it is made of polyethylene with increased heat resistance. This concept does not mean that cross-linking technology was applied to it, since the unique PE-RT material already has all the necessary qualities. A distinctive feature of the PERT pipe is the possibility of connection in the circuit by welding or fittings. Regardless of the type of work performed, PERT does not lose its strength and plasticity.
PERT polyethylene is also used in the production of metal-plastic pipes, the distinguishing feature of which is the presence of an inner aluminum layer. If a PE-RT pipe is produced without an inner metal layer, it is protected from oxygen penetration by other means, for example, by an OXYDEX airtight layer.
A water heated floor, mounted from a PERT pipe, has higher performance characteristics. This material, unlike PEX, has increased elasticity and the ability to tolerate heat up to 124.7°C. Considering the lower production cost of PE-RT polyethylene, the arrangement of underfloor heating systems from PE-RT pipes is somewhat cheaper, while meeting all the requirements for this heating method.
Video: Warm water floor
