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 the penetration of oxygen 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 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 µm), the pipes are not subject to overgrowth, so 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 >>>
Today, unfortunately, marketing moves and advertising tricks are increasingly affecting various technical solutions and the choice of a particular material and equipment for a project. More and more often, instead of a full-fledged technical passport or catalog for equipment, designers have advertising booklets and brochures on their desks, according to which they select. What is unacceptable to write in serious technical literature migrates to the pages of such booklets. Often, marketers assign overestimated or completely non-existent indicators to their product, misleading engineers. As a rule, outstanding technical features of the equipment in booklets are presented as undeniable advantages. Conversely, any technical information about competitive products is presented as significant and irreparable flaws.
All these factors ultimately lead to the wrong choice of materials and equipment, which can eventually lead to an emergency. The fault in this case falls on the shoulders of the design engineer, since any manufacturer, along with colorful advertising that triumphantly describes all the delights of the product, has either footnotes in small print or a technical data sheet carefully hidden from the human eye with real data. Most often, advertising brochures provide information that does not contradict the passport data, but is presented in such a way that people have a false idea about the real technical features of the product. For example, the phrases “a pipe can withstand a temperature of 95 ºС and a pressure of 10 bar” and “a pipe can withstand a coolant temperature of 95 ºС at a pressure of 10 bar for 50 years” are fundamentally different from each other. In the first case, a riddle is posed: is the pipe capable of withstanding 95 ºС coolant temperature and 10 bar at the same time, or are these two critical points for the application of this pipe? And most importantly, there is no time indicator, that is, it is not known how long the pipeline can withstand these parameters - five minutes, an hour or 50 years?
This article lists the main marketing gimmicks and myths propagated by the PEX pipe manufacturers.
1st group of myths - about the superiority of one stitching method over another
Almost every manufacturer of PEX pipes claims that it is the method of sewing their pipes that is the best, while others are no good. Only polyethylene cross-linked according to their method will have increased strength characteristics and reliability indicators.
To begin with, I would like to recall some information about the crosslinking of polyethylene. By cross-linking is meant the creation of a spatial lattice in high-density polyethylene due to the formation of volumetric cross-links between polymer macromolecules. The relative amount of cross-links formed per unit volume of polyethylene is determined by the “degree of cross-linking”. The degree of crosslinking is the ratio of the mass of polyethylene covered by three-dimensional bonds to the total mass of polyethylene. In total, four industrial methods for crosslinking polyethylene are known, depending on which the crosslinked polyethylene is indexed by the corresponding letter.
Table 1. Types of crosslinking of polyethylene
Peroxide crosslinking (method "a")
Method "a" is a chemical crosslinking of polyethylene using organic peroxides and hydroperoxides.
Organic peroxides are derivatives of hydrogen peroxide (HOOH) in which one or two hydrogen atoms are replaced by organic radicals (HOOR or ROOR). The most popular peroxide used in pipe production is dimethyl-2.5-di-(bytylperoxy)hexane. Peroxides are highly hazardous substances. Their production is a technologically complex and expensive process.
To obtain PEX according to method "a", polyethylene is melted together with antioxidants and peroxides before extrusion (Thomas Engel process), rice. 1.1. With an increase in temperature to 180–220 ºС, peroxide decomposes, forming free radicals (molecules with a free bond), rice. 1.2. Peroxide radicals are taken from the polyethylene atoms by one hydrogen atom, which leads to the formation of a free bond at the carbon atom ( rice. 1.3). In neighboring polyethylene macromolecules, carbon atoms that have free bonds are combined ( rice. 1.4). The number of intermolecular bonds is 2–3 per 1000 carbon atoms. The process requires tight temperature control during the extrusion process, when pre-crosslinking occurs, and during further heating of the pipe.
Method "a" is the most expensive. It guarantees complete volumetric coverage of the mass of material by the action of peroxides, as they are added to the initial melt. However, this method requires that the crosslinking be at least 75% (according to Russian standards - not less than 70%), which makes pipes made of this material more rigid than other methods of crosslinking.
Silane crosslinking (method "b»)
Method "b" is a chemical cross-linking of polyethylene using organosilanes. Organosilanides are silicon compounds with organic radicals. Silanides are poisonous substances.
Currently, for the production of PEX pipes according to the “b” method, vinyltrimethoxyloxane (H 2 C=CH)Si(OR) 3 ( rice. 2.1). When heated, the bonds of the vinyl group are destroyed, turning its molecules into active radicals ( rice. 2.2). These radicals replace the hydrogen atom in polyethylene macromolecules ( rice. 2.3). Then polyethylene is treated with water or water vapor, while organic radicals attach a hydrogen molecule from water and form a stable hydroxide (organic alcohol). Neighboring polymer radicals are closed through the Si-O bond, forming a spatial lattice ( rice. 2.4). Water displacement from PEX is accelerated by a tin catalyst. The process of final cross-linking takes place already in the solid stage of the product.
Radiation crosslinking (method "c")
The "c" method consists in exposing the C-H group to a stream of charged particles ( rice. 3.1). It can be a stream of electrons or gamma rays. With this exposure, some of the C-H bonds are destroyed. The carbon atoms of neighboring macromolecules, from which a hydrogen atom was knocked out, combine with each other ( rice. 3.3). Irradiation of polyethylene by a stream of particles occurs already after its molding, that is, in a solid state. The disadvantages of this method include the inevitable uneven crosslinking.
It is impossible to position the electrode so that it is equidistant from all areas of the irradiated product. Therefore, the resulting pipe will have uneven crosslinking along the length and thickness.
The cyclic electron accelerator (betatron) is most often used as an irradiation source, which is relatively safe both in production and in the use of the finished pipe.
Despite this, in many European countries the production of pipes sewn by the "c" method is prohibited.
To reduce the cost of the crosslinking process, radioactive cobalt (Co 60) is sometimes used as a radiation source. This method is certainly cheaper, since the pipe is simply placed in a chamber with cobalt, but the safety of using such pipes is very doubtful.
Misconception #1 : “The cross-linking method (PEX-a) is better than others in terms of the strength of the resulting material, because the regulated minimum degree of cross-linking for this method is greater than for other methods. And the greater the degree of crosslinking of PEX, the stronger the material.”
Indeed, GOST R 52134 regulates a different minimum allowable degree of crosslinking of PEX pipes for different manufacturing methods ( tab. one), and it is true that as the degree of crosslinking increases, the strength of the pipes increases.
However, it is unacceptable to compare the degrees of crosslinking of PEX-a, PEX-b and PEX-c, since the molecular bonds of these materials formed as a result of crosslinking have different strengths, and therefore, even these types of polyethylene crosslinked to the same degree will have different strengths. The bond energy of the C-C type that is formed in the polyethylene cross-linked by the "a" and "c" methods is about 630 J/mol, while the bond energy of the Si-C type that is formed in the polyethylene cross-linked by the "b" method is 780 J/mol. The physicochemical and technical properties are also affected by the interaction of macromolecules due to hydrogen bonds that arise in the polymer due to the presence of polar groups and active atoms, as well as the formation of associates as a result of the interaction of the cross bonds themselves. This is primarily characteristic of a silanol-crosslinked polymer, where there are a large number of silanol groups capable of forming additional engagement sites in amorphous regions, increasing the density of the structural network (which is 30% higher than with peroxide and 2.5 times higher than with irradiation). crosslinking) and reduce deformability at high temperatures.
Bench tests of cross-linked polyethylene pipes show some strength advantage of silane cross-linking. So, at a test temperature of 90 °C for pipes with a diameter of 25 mm and a length of 400 mm, the fracture pressure of pipes made of PEX-a, PEX-b and PEX-c was 1.72, 2.28 and 1.55 MPa, respectively (B.C Osipchik, E.D. Lebedeva, "Comparative analysis of the performance properties of polyolefins crosslinked by various methods and improvement of the physicochemical characteristics of silanol-crosslinked polyethylene", May 24, 2011).
Thus, claims that PEX-a is the strongest material due to the greater degree of cross-linking are not true. This factor is rather a disadvantage than an advantage of this crosslinking method.
The stitching method is not the most important indicator of a pipe when choosing it. First of all, you should make sure that the polyethylene from which the pipe is made is really cross-linked. Some manufacturers do not sew or do not sew the pipe at all, while indicating the same characteristics on it as on high-quality PEX pipes.
For example, in May 2013, GROSS pipes were withdrawn from circulation in Ukraine. Under this brand, pipes made of cross-linked polyethylene were distributed, on the pipes themselves there was a PEX marking ( rice. 4), but in fact these pipes consisted of ordinary non-crosslinked polyethylene, is it worth talking about their performance? There is an easy way to determine what is in front of you - cross-linked polyethylene or a fake made from ordinary polyethylene. To do this, a piece of pipe must be heated to a temperature of 150–180 ºС, ordinary polyethylene loses its shape at this temperature, and cross-linked due to intermolecular bonds retains its shape even at such high temperatures ( rice. 5).
Rice. 4. Marking on pipe Gross
Rice. 5. Pipes Gross (sample 7) and VALTEC PEX-EVOH (sample 6) after heating in an oven for 30 minutes at a temperature of 180 ºС
Misconception No. 2: “Only polyethylene crosslinked according to the “a” method has the properties of temperature memory, polyethylene crosslinked by other methods does not have this property.
What is meant by the "temperature memory effect" in this case? The essence of this effect is that the pre-deformed pipe, after heating, restores its original shape, which it had before deformation. This property manifests itself due to the fact that during bending and deformation, the molecularly bonded areas are compressed or stretched, while accumulating internal stress. After heating in places of deformation, the elasticity of the material decreases. Internal stresses accumulated during the deformation process create forces in the thickness of the “softened” material directed towards the original shape of the pipe. Under the influence of these efforts, the pipe tends to recover.
Rice. 6.1. pipe fractureVALTEC PEX- EVOH(crosslinking method - PEX-b) and its recovery after heating to 100 °C
Rice. 6.2. Fracture of a PEX-a pipe with an anti-diffusion layer and its recovery after heating to 100 °C
Rice. 6.3. Fracture of a pipePEX- c without an anti-diffusion layer and its recovery after heating to 100 ° C (uncolored cross-linked polyethylene becomes transparent at high temperatures)
In figures 6.1 – 6.3 shows the restoration of pipes with various stitching methods after a break. With all methods of stitching, the pipes restored their original shape. Wrinkles formed on pipes coated with an anti-diffusion layer after restoration. In these places, the anti-diffusion layer has delaminated from the PEX layer. This does not affect the characteristics of the pipe, since the working layer is a PEX layer that has been completely regenerated.
The memory effect is inherent in any cross-linked polyethylene. The only difference between PEX-a in the recovery technique is that PEX-a crosslinks during extrusion, and the original shape that the pipeline seeks to return to is straight. PEX-b and PEX-c, as a rule, are sewn together after being formed into coils, and, accordingly, the shape to which the pipelines will tend is a circle with a radius equal to the radius of the coil.
Misconception No. 3: “B-linking does not provide the required hygiene of pipes, since the silanes used in the production of these pipes are toxic.”
Indeed, silanes (SiH 4 - Si 8 H 18), used to obtain PEX-b, are extremely toxic. However, silicic acid for polyethylene crosslinking is used only in the cable industry. For the production of pipes, organosilanides are used, which are also poisonous, but their distinctive feature is that when cross-linked, they either completely go into a chemically bound state, or turn into chemically neutral organic alcohol, which is washed out during hydration of pipelines. To date, the most common reagent for cross-linking polyethylene using the “b” method is vinyltrimethoxylane (simplified formula: C 2 H 4 Si (OR) 3).
The main indicator of the safety of the pipeline and fittings is the hygienic certificate. Only pipes and fittings that carry this certificate are approved for installation in potable water systems.
Misconception No. 4: “Only PEX-a pipes have a uniform degree of cross-linking throughout the cross section, while other pipes have uneven cross-linking.”
The main advantage of "a" crosslinking is that peroxides are added to the molten polyethylene before it is extruded into the pipe, and pipe crosslinking with due attention to temperatures and peroxide dosages will be uniform.
When cross-linked polyethylene pipelines were not widely used, cross-linking using the “b” and “c” methods did have a drawback, which consisted in uneven cross-linking along the length and width of the pipeline. However, when the volume of pipe production reached several kilometers per week, the question arose of improving the quality and automation of these types of stitching. Using the silane method, it is possible to evenly sew the pipeline by choosing the right dosage of reagents, accurately maintaining the temperature and time parameters of pipe processing, and also using catalysts (tin).
In addition, the modern method of introducing silane differs from the original one, if earlier silane was added to the polyethylene melt during extrusion (B-SIOPLAST method), now, as a rule, silane is pre-mixed with peroxide and a certain amount of polyethylene and only then added to the extruder (method B-MONOSIL).
Plants producing large volumes of pipes, by trial and error, have long reached the ideal crosslinking technology, and production automation has made it possible to obtain pipes with stable characteristics. Thus, the problem of uneven sewing of the pipeline remains only in small, non-automated industries.
Misconception #5: "PERT is a type of cross-linked polyethylene, and is not inferior to it in terms of performance."
Heat-resistant polyethylene PERT is a relatively new material used for the production of pipes. Unlike conventional polyethylene, which uses butene as a copolymer, PERT uses octene (octylene C 8 H 16) as a copolymer. The octene molecule has an extended and branched spatial structure. Forming side branches of the main polymer, the copolymer creates an area of intertwined copolymer chains around the main chain. These branches of neighboring macromolecules form spatial cohesion not due to the formation of interatomic bonds, as in PEX, but due to the cohesion and interweaving of their “branches”
Heat-resistant polyethylene has a number of properties of cross-linked polyethylene: resistance to high temperatures and ultraviolet rays. However, this material does not have long-term resistance to high temperatures and pressures, and is also less acid-resistant than PEX. On the rice. 7 graphs of the long-term strength of cross-linked polyethylene PEX and high-temperature polyethylene PERT are presented, taken from GOST R 52134-2003 with change No. 1. As can be seen from the graphs, cross-linked polyethylene loses little in its strength over time, even at high temperatures. At the same time, the graph of the drop in strength is straight and easily predictable. For PERT, the graph has a kink, and at high temperatures, this kink occurs after two years of operation. The break point is called critical, when this point is reached, the material begins to actively accelerate the loss of strength. All this leads to the fact that the pipe, which has reached a critical point, very quickly fails.
Rice. 7. Reference curves of long-term strength of pipes made of PEX (left) and PERT (right)
In addition, due to the lack of bonds between macromolecules, PERT does not have the properties of temperature memory.
Misconception No. 6: "PEX pipes can be unconditionally used for radiator heating systems."
The conditions for the applicability of plastic and metal-plastic pipelines on the territory of the Russian Federation are regulated by GOST 52134-2003. Since the strength of plastic pipelines is quite significantly affected by the time of exposure to a coolant with a certain temperature, they have operating classes ( tab. 2), which reflect the nature of the impact of certain temperatures on the pipe during the entire service life.
Table 2. Operation classes of polymer pipelines
| Operating class | Application area | T slave, °C | Time at T slave; years | T max, °C | Time at T max, years | T avar, °C | Time at T accident, h |
| Hot water supply (60 °С) | |||||||
| Hot water supply (70 °С) | |||||||
| Low temperature floor heating High temperature floor heating | |||||||
| Low-temperature heating with heating devices | |||||||
| High-temperature heating with heating devices | |||||||
| Cold water supply |
At the same time, the use of pipelines in heating and water supply systems is limited by paragraphs 5.2.1 and 5.2.4:
“5.2.1 Pipes and fittings made of thermoplastics should be used in water supply and heating systems with a maximum working pressure P max 0.4; 0.6; 0.8 and 1.0 MPa and temperature conditions indicated in Table 26. The following classes of operation of pipes and fittings are established ... "
"5.2.4 Other operating classes may be established, but temperatures shall not exceed those specified for class 5."
In other words, the manufacturer can set any ratio of the time of influence of various temperatures. However, the maximum operating temperature must not be set above 90 °C. In most heating systems, the design temperature of the coolant is 95 °C. From here the data follows the conclusion: in old systems, PEX pipes are unacceptable to use. And if these pipes are used for high-temperature radiator heating, then only in a system that is designed for a maximum operating temperature of 90 ° C.
But why do most advertising products of PEX pipe manufacturers indicate a maximum operating temperature of 95 ° C? The fact is that in clause 5.2.1 GOST establishes standards only for the use of plastic pipes, in other words, it regulates the types of systems in which pipes can be used, but not the pipelines themselves, which gives manufacturers the right to write almost any operating temperature in the technical characteristics of pipes .
“The difference is only 5°C does not significantly affect the long-term strength of the pipe”- can be heard as a justification for the use of a pipe. But the pipe has three main parameters: temperature, pressure and service life, and if you increase one of the parameters, then the other two will inevitably decrease. Thus, it is possible to use the pipe at higher temperatures, but one must take into account the fact that this will inevitably cause a reduction in service life. The minimum allowable service life of pipelines according to SNiP 41-01-2003 is 25 years, and if the pipelines are laid hidden in the building structure, the service life must be at least 40 years. With an increase in the operating temperature to 95 ° C, the service life of the pipeline is reduced to 35–40 years, depending on the wall thickness, hence it can be concluded that pipes with such application parameters cannot be laid covertly.
Below are examples of the use of supplier omissions when specifying technical specifications:
The operating temperature of 95 ºС at a pressure of 0.8 MPa cannot correspond to a service life of 50 years. From the chart on rice. 5 it can be seen that the maximum service life of the pipeline at a temperature of 95 ºС is 8 years.
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The maximum operating temperature of 95 ºС and the service life of 50 years are indicated, but it is silent that this temperature can act on the pipe for a maximum of 1 year out of these 50 years.
Misconception No. 7: “The oxygen-protective layer of the pipeline is a marketing ploy and does not have any effect on performance ...”
The use of an oxygen-protective layer is primarily due to the fulfillment of the requirements of SNiP 41-01-2003 "Heating, ventilation and air conditioning" paragraph 6.4.1
“... Polymer pipes used in heating systems together with metal pipes (including in external heat supply systems) or with instruments and equipment that have restrictions on the content of dissolved oxygen in the coolant must have an oxygen permeability of not more than 0.1 g / m day ... »
The oxygen permeability of a pipe made of cross-linked polyethylene with a wall thickness of 2 mm and a diameter of 16 mm at an air temperature of 20 ºС is 670 g/m³·day. Obviously, a conventional XLPE pipe does not meet the requirements of this SNiP. The requirements of SNiP did not appear by chance, the fact is that a specially prepared coolant is used in heating and heat supply systems. Water in boiler houses or in heating points is deaerated using special installations. All this is done in order to prevent corrosion of steel and aluminum elements of the system, which, one way or another, are present in any system.
To understand the detrimental effect that oxygen gives in the coolant, let us explain the process of steel corrosion itself. Steel corrodes both in water in which oxygen is dissolved and in deaerated water, but the course of the process is somewhat different.
In oxygen-free water, corrosion proceeds as follows: under the influence of water, some of the iron atoms go into solution, as a result of which a negative charge of iron atoms (Fe 2+ + 2e -) accumulates on the surface of the steel. In water, due to the presence of impurities, cations and anions H + and OH - are formed. Iron ions with a negative charge, which have gone into solution, combine with anions of the hydrogen group, forming an iron hydrate that is poorly soluble in water (it is this substance that gives the brown, rusty color to the coolant): Fe 2+ + 2OH - → Fe (OH) 2.
Hydrogen cations (H +), having a positive charge, are attracted to the inner surface of the pipe, which has a negative charge, forming atomic hydrogen, which forms a protective layer on the surface of the pipe (hydrogen depolarization), which reduces the corrosion rate.
As you can see, the corrosion of steel in the absence of oxygen is temporary, until the entire inner surface of the pipe is covered with a protective film, and the reaction slows down.
In the case when steel comes into contact with water containing oxygen, corrosion occurs differently: the oxygen contained in the water binds hydrogen, which forms a protective layer on the iron surface (oxygen depolarization). And ferrous iron is oxidized to ferric:
4Fe(OH) 2 + H 2 O + O 2 → 4Fe(OH) 3,
nFe(OH) 3 + H 2 O + O 2 → xFeO yFe 2 O 3 zH 2 O.
Corrosion products in this case do not form a protective layer tightly adjacent to the metal surface. This is due to the increase in volume that occurs during the transition of iron hydroxide to ferrous oxide hydrate, and the "swelling" of the iron layer subject to corrosion. Thus, the presence of oxygen in water significantly accelerates the corrosion of steel in water.
The elements that suffer from corrosion in the first place are boilers, pump impellers, steel pipelines, taps, etc.
How does oxygen penetrate through the thickness of polyethylene and dissolve in water? This process is called diffusion of gases, a process in which a gaseous substance can penetrate through the thickness of an amorphous material due to the difference in partial pressures of this gas on both sides of the substance. The energy that allows the gas to pass through the thickness of the plastic arises as a result of the difference in the partial pressures of oxygen in air and oxygen in water. The partial pressure of oxygen in air under normal conditions is 0.147 bar. The partial pressure in absolutely deaerated water is 0 bar (regardless of the coolant pressure) and increases as the water is saturated with oxygen.
Rice. 8. EVOH layer of VALTEC PEX-EVOH pipe at x100 magnification
It is not difficult to quantify the harm that a pipe without an oxygen barrier can cause.
For example, let's take a heating system with pipes made of cross-linked polyethylene without an oxygen barrier. The total length of pipes with an outer diameter of 16 mm is 100 m. During the year of operation of this system, the following will enter the water:
Q = D O 2 ( d n - 2 s) 2 l · z\u003d 650 (0.16 - 2 0.002) 2 100 365 \u003d 3416 g of oxygen.
In the above formula D O 2 - oxygen permeability coefficient, for PEX pipes with an outer diameter of 16 mm and a wall thickness of 2 mm, it is 650 g / m 3 · day; d n and s- the outer diameter of the pipeline and its thickness, respectively, m, l– pipeline length, m, z- number of days of operation.
In the coolant, oxygen will be in the form of O 2 molecules.
The mass of iron that entered into the oxidation reaction can be calculated using the stoichiometric calculation of the equations for the oxidation of ferrous iron (2Fe + O 2 → 2FeO) and subsequent oxidation to ferric iron (4FeO + O 2 → 2Fe 2 O 3).
In the oxidation reaction of ferrous iron, its mass will be equal to:
m Fe = m o2· n Fe· M Fe /(nO 2 · M O2) = 3416 2 56 / (1 32) = 11 956
In this calculation m Fe is the mass of ferrous iron that has reacted, g, m o 2 is the mass of oxygen that entered into the reaction, g, n Fe and nO2- the amount of the substance that entered into the reaction: (iron, Fe, - 2 mol, oxygen, \u003d yes, O 2, - 1 mol), M Fe and M O 2 - molar mass (Fe - 56 g / mol; O 2 - 32 g / mol).
In the oxidation reaction of ferric iron, its mass will be equal to:
m Fe = m o2· n Fe· M Fe /(nO 2 · M O2) = 3416 4 56 / (3 32) = 7970
Here, the amount of the substance that reacted with iron ( n Fe) is 4 mol oxygen ( nO2) - 3 mol.
It follows that when 3416 g of oxygen enters the coolant, the total amount of iron subject to corrosion will be 11,956 g (11.9 kg), while 7,970 g (7.9 kg) of iron forms a rusty layer on the steel walls, and 11,956 - 7,970 = 3,986 (3.98 kg) of iron will remain in a divalent state and enter the coolant, polluting it. For comparison: if we take the oxygen permeability of the pipeline as the maximum allowable according to the norms (0.1 g / m 3 day), then 0.52 g of oxygen per year will dissolve in water, which will lead to corrosion of a maximum of 1.82 g of iron, that is, in 6,500 times less.
Of course, not all oxygen entering the pipe interacts with iron, some of the oxygen will interact with impurities in the coolant, and some can reach the deaeration station, where it will be removed from the coolant again. However, the danger of the presence of oxygen in the system is very significant and by no means exaggerated.
Sometimes in publications there is a phrase: “... automatic air vents will remove all oxygen that has entered through the walls of the pipeline". This statement is not entirely true, since an automatic air vent can release oxygen only if it is released from the coolant. Release of dissolved gases occurs only when the flow rate or pressure is abruptly reduced, which is rare in conventional systems. To remove oxygen, special flow-through deaerators are installed, in which there is a sharp decrease in speed and the removal of released gases. On the rice. 9.1 and 9.2 shows the usual version of the installation of the air vent and the version with a deaeration chamber. In the first case, the air vent removes only a small amount of gases accumulated in the pipeline, in the second - gases that are forcibly “extracted” from the flow due to a sharp increase in the cross section and a decrease in speed.
Misconception No. 8: “The temperature elongation of PEX pipes is many times higher than the temperature elongation of other materials, due to such a large temperature elongation, the embedded pipe breaks the screed and plaster ...”
As usual, these myths are based on reliable facts (the temperature elongation of a pipe made of cross-linked polyethylene is almost 8 times greater than that of a metal-plastic pipe), but the conclusion is made incorrect.
In order to find out whether the destruction of the floor screed will occur or not, it is necessary to understand the processes taking place in a monolithic pipe.
The pipeline laid in the open, when heated to a certain temperature, will begin to lengthen. The relative elongation of the pipeline is easy to calculate by the formula:
Δ L = k t · Δ t · L,
where k t- coefficient of thermal elongation of the pipe material, Δ t- the difference between the temperature of the coolant and the air temperature during pipe installation; L- pipeline length.
Rice. ten
But in the floor screed, the pipe cannot lengthen, since the cement-sand screed prevents its thermal expansion. In this case, for each unit of pipeline extension, the tie will compress it by the same distance. Ultimately, the pipeline will be compressed by the floor screed to a distance equal to its thermal elongation ( rice. eleven), its length will not change. The question arises, where does the extra piece of pipe go. The fact is that a certain force is required to compress the pipe. The elongated section of the pipe simply turns into stress, which the pipe exerts on the floor screed. And the answer to the question of whether the screed will withstand the thermal stress of the pipe depends only on what stress the pipe will exert on the screed.
Rice. eleven
The stress that the pipeline exerts on the floor screed can be estimated using Hooke's Law, the elastic deformation of materials. The voltage that the pipe will give will be equal to:
N = Δ L · s · e / L,
where s is the cross-sectional area of the pipeline walls, e is the elasticity modulus of the pipeline material, L- pipeline length.
But even if a certain voltage value is obtained for a specific pipe, then there will be little practical benefit from this, since this value must be compared with the maximum allowable floor screed stress, and based on this comparison, a conclusion can be drawn about the use of this pipe. But it is quite difficult to calculate the maximum allowable stress in the screed, and the resulting value, as a rule, will not be accurate, since there are bumps and stress concentrators in the screed, etc.
But using this formula, you can compare the pipelines with each other in terms of the voltage that they exert on the screed. If we substitute in the stress formula, the formula for thermal elongation, we get:
N = k t Δt L s e / L = k t t s e.
For a metal-plastic pipe with a diameter of 16 mm, when it is heated by 50 ° C, the stress in the screed is:
N= 0.26 10–4 50 8.7 10–5 8400 = 9.5 10–4 MPa.
N= 1.9 10–4 50 8.7 10–5 670 = 5.5 10–4 MPa.
N= 0.116 10–4 50 16.2 10–5 200,000 = 187.9 10–4 MPa.
Thus, it can be seen that PEX exerts less stress on the screed than a similar metal-plastic pipe. The load from the pipeline on the screed depends not only on the thermal expansion of the pipeline, but also on the modulus of elasticity, which is relatively low for cross-linked polyethylene compared to other types of materials. Steel, due to the high modulus of elasticity, despite the lowest coefficient of thermal expansion, causes much more stress in the screed than pipes with high thermal expansion.
Misconception No. 9: "You cannot mount a PEX pipe using press fittings, since the property of temperature memory is not involved in the process of ensuring tightness."
To date, two types of connections are used to connect PEX pipelines: press fittings and fittings with a compression sleeve.
First you need to understand the mechanism for connecting press fittings:
After pressing the fitting with a press tool, the outer steel sleeve is deformed, squeezing the polyethylene wall. At the same time, polyethylene is also deformed, and due to the accumulated stress in the spatial bonds of molecules, polyethylene tends to return to its original shape (shape memory). Since the modulus of elasticity of steel is many times greater than the modulus of elasticity of cross-linked polyethylene, it is not the sleeve that undergoes deformation, but polyethylene, which goes deeper into the grooves of the fitting and seals the joint. Rubber rings in this case serve two main purposes:
First ring (on rice. 12 left) is outside the crimping area of the press tool. It is used to ensure tightness in case of small movements of the fitting during operation (such movements can be caused by temperature fluctuations). The modulus of elasticity of EPDM (the material from which the sealing gum is made) is many times less than the modulus of elasticity of PEX, so this material in such cases fills all the voids formed as a result of fitting displacement.
Rice. 12. Compression of the VALTC PEX-EVOH pipe with a press fitting
The second ring is partially in the compression zone (on rice. 12 on right). This ring is constantly under load from the steel sleeve. It serves to compensate for the difference in thermal expansion of polyethylene and brass. With sudden heating or sudden cooling of the fitting, a situation may arise when a micron gap appears between the fitting and the pipe wall, which, although it will not lead to leakage, will significantly reduce the service life of the connection. This ring in this case will fill the resulting gap and ensure tightness.
Pipes made of cross-linked polyethylene using the "b" method are not mounted using compression sleeve fittings due to the fact that during such installation the end of the pipe is expanded using an extractor. The elongation at break of PEX-b compared to PEX-a is lower due to stronger silane bonds. Therefore, the expansion procedure for the PEX-b pipeline leads to the accumulation of microcracks, which shorten the service life of the connection.
The press fitting provides reliable and hermetic fixation of the pipeline during the entire working period.
Conclusion
On the one hand, the use of modern materials leads to cheaper production, faster installation, environmental friendliness and safety. All these factors lead to an improvement in the quality of human life. But at the same time, unhealthy competition between manufacturers of modern materials causes fear of consumers in the perception of everything new, and also significantly complicates the choice of one or another material.
» PE-RT pipes - characteristics of new plumbing pipes
The popularity of PEX plumbing pipes made of cross-linked polyethylene was suddenly called into question. And no one else did it, but the manufacturer himself. The American company "Legend" recognized the undeniable popularity of PEX and at the same time noted the negative properties of this product. A series of PEX pipes was marked by a serious operational drawback - residual traces of chemistry in the composition of the water. Plus, recycling and recycling promises a lot of difficulties. Therefore, the new PE-RT plumbing pipes, based on bimodal polyethylene, are confidently replacing the PEX series from the leading position in the plumbing market.
PE-RT series for sanitary ware
The American company "Legend" in 2015 began to produce innovative sanitary products that are functionally and technically more advanced.
Polyethylene plumbing hoses for heating and hot water, marked with the HyperPure PE-RT brand, increase the efficiency and productivity of the hydraulic system.
GOST 32415-2013
Available sizes:
The COMPIPE TM pressure pipe made of polyethylene of increased temperature resistance (PERT) with a barrier (anti-diffusion) layer of ethylene vinyl alcohol (EVOH) is intended for the construction and repair of internal networks of cold, hot water supply and radiator heating of buildings, including underfloor heating (operation classes 1, 2 , 4, ХВ according to GOST 32415-2013).
PERT/EVOH COMPIPE TM pipes are ideal for low temperature underfloor heating systems.
The PERT/EVOH COMPIPE TM pipe is made from DOWLEX 2388 new generation PE-RT type II heat stabilized polyethylene manufactured by The Dow Chemical Company. DOWLEX 2388 - polyethylene with high temperature resistance and resistance to aging is produced by the method of directed spatial formation of side bonds in polymer macromolecules by copolymerization of butene and octene (Fig. 1). In the process of synthesis, an area of intertwined chains is formed around the main chain, due to which neighboring macromolecules are mutually intertwined, forming spatial cohesion. Thanks to this structure, PERT, like PEX, has increased long-term heat resistance and strength, but retains the flexibility inherent in conventional polyethylene.
Figure 1. Synthesis of high temperature resistant polyethylene - copolymerization of butene and octene.
The PERT/EVOH COMPIPE TM pipe meets the requirements of SNiP 41-01-2003, which prescribes the use of polymer pipes with an oxygen permeability index of not more than 0.1 g/m 3 per day in heating systems (requirements are also GOST 32415-2013, DIN 4726).
Pipe specifications are shown in Table 1.
Table 1
| Name of indicator | COMPIPE™ PERT/EVOH | |||
| Outer diameter, mm | 16 | 20 | ||
| Inner diameter, mm | 12 | 16 | ||
| Wall thickness, mm | 2,0 | 2,0 | ||
| vendor code |
1620200-5 /1620100-5 |
2020100-5 | ||
| Coil length, m | 200/600 | 100 | ||
| S-series | 3,5 | 4,5 | ||
| SDR standard size ratio | 8 | 10 | ||
| Weight 1 p.m. pipes, g | 82 | 131 | ||
| The volume of liquid in 1 p.m. pipes, l | 0,113 | 0,201 | ||
| Working temperature | (0÷80)ºС | |||
| Emergency temperature (no more than 100 hours) | 100ºС | |||
|
Max working pressure 1, 2, 4 grades |
0.8 MPa |
0.6 MPa |
||
|
Maximum working pressure at 20ºС |
1.0 MPa | |||
| Thermal linear expansion coefficient | (1.95x10 -4) K -1 | |||
| Change in the length of the pipe after heating at a temperature of 120ºС for 60 minutes | less than 2% | |||
| Equivalent uniform-grain roughness coefficient | 0,004 | |||
| Coefficient of thermal conductivity | 0.4 W/m K |
|||
| Diffusion of oxygen | less than 0.1, g / m 3 per day | |||
| Warranty period, years | 10 | |||
| Service life subject to the rules of installation and operation, years | 50 | |||
Table 2. Table of characteristics of operation classes according to GOST R 32415-2013
| Operating class | T slave, °C | Time at T pab, year | Tmax, °C |
Time at T max, year |
T avar,°C | Time at T accident, h | Application area |
| 1 | 60 | 49 | 80 | 1 | 95 | 100 | Hot water supply (60 o C) |
| 2 | 70 | 49 | 80 | 1 | 95 | 100 | Hot water supply (70 o C) |
| 4 | 20 | 2,5 | 70 | 2,5 | 100 | 100 |
High temperature outdoor |
| 40 | 20 | ||||||
| 60 | 25 | ||||||
| 5 | 20 | 14 | 90 | 1 | 100 | 100 | High temperature heating heating appliances |
| 60 | 25 | ||||||
| 80 | 10 | ||||||
| XV | 20 | 50 | - | - | - | - | Cold water supply |
|
The following designations are accepted in the table: T slave - operating temperature or a combination of temperatures of the transported water, determined by the scope; T max - maximum operating temperature, the action of which is limited in time; T accident - emergency temperature that occurs in emergency situations in violation of control systems. HOW TO USE THE TABLE |
|||||||
Table 3. Package characteristics of COMPIPE TM PERT/EVOH pipes
The pipe has a certificate of conformity in the Rostest system in accordance with GOST 32415-2013, a certificate of state registration.
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 tiles 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, which 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 a decrease in the load intensity, it will take the originally specified shape.
Crosslinking of polyethylene is carried out using different technologies, denoted 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 crosslinking 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
