Advantages of metal-plastic pipes for water supply and installation rules

Metal-plastic on cold and hot water connections

It is believed that metal-plastic is not the best material for installing heating and distributing hot water: after a while, the pipe may leak at the connection with the fitting. Today we have to figure out whether metal-plastic pipes are suitable for heating and water supply and what are the reasons for numerous complaints about leaks.

What it is

What are metal-plastic pipes for water supply and heating?

A multi-layer construction, usually consisting of three layers: two polyethylene shells (outer and inner) and an aluminum core. The core provides strength in relation to hydrostatic pressure, the shell - corrosion resistance and low hydraulic resistance.

Modern metal-plastic pipes for cold and hot water supply are produced in several modifications:

• Not only ordinary PE-polyethylene, but also cross-linked PE-X or thermally modified PE-RT can be used as a shell material. The first provides greater tensile strength, the second - increased heat resistance (up to 110 ° C);

PE-RT sheathed pipe

• The core can be not only solid, but also mesh.

Useful: in the Russian Federation, pipes are manufactured according to technical specifications TU 2290-001-12333095-96. There is no standard governing their production.

What to consider when choosing

The initial data for the choice of pipe materials are the properties of the water entering the hot water system.

They are regulated by SNiP 2.04.01 - 85.

According to the requirements of the document, the maximum water temperature in the system is set at 75 degrees, the recommended values ​​are 50 and 60 degrees for open and closed systems, respectively.

However, hot water suppliers in cities, especially in regions with harsh climates, rarely adhere to these recommendations, and hot water with temperatures up to 100 degrees is not uncommon in pipes.

The situation in private houses, where the consumer regulates the temperature of the water at the outlet of the heating device, independently, is somewhat simpler.

When choosing materials, water quality also plays a role.

Hard hot water entering the pipes leads to intensive deposits of limescale on their walls.

The reagents used to soften it, especially in centralized water supply systems, often belong to groups of substances with high chemical activity.

These factors determine the basic requirements for the materials of DHW pipelines.

Do you know the scheme by which grease traps are made for the sewerage system for a restaurant? Read the helpful resource on protecting pipelines from deposits. The information will help to extend the intervals between cleaning the collection system.

Read about the best dishwasher detergent on this page.

Origins

Metal-plastic began its triumphant march across the Russian expanses in the mid-90s. The reasons for its exceptional popularity boiled down to a striking contrast to the then massively used black steel pipes:

• The appearance of pipes and fittings allowed open installation and did not require painting or any other finishing. Snow-white pipes and shiny fittings did not spoil the appearance of the room or bathroom, but decorated the room;

Pipes and fittings are quite capable of becoming part of the design of the room.

• The pipes were not overgrown with rust and mineral deposits, maintaining their capacity throughout the entire period of operation;
• Manufacturers and sellers have promised an exorbitant life span of 50 years or more;

Reference: black steel serves no more than 25 years in cold water. The author came across the first leaks at the seams of water and gas supply (WGP) pipes 10 years after the commissioning of a new house.

• Finally, the main thing: the installation of water supply with metal-plastic pipes was within the power, according to one seller from a plumbing store, "an eighth-grader with two adjustable wrenches." It did not require special skills, a complex instrument and took very little time.

A pair of adjustable wrenches is sufficient to assemble the connection.

The nuances of choosing metal-plastic pipes for water supply

To install a water supply system in a house, when choosing pipes, you should take into account the following nuances. Follow the marking on the pipe, it should contain: place of production, product dimensions, temperature regime, symbol, batch size, pressure class and type of material.

It is worth paying attention to the appearance of the pipe. There should be no defects on its walls; a smooth surface is required. Scratches and foreign inclusions are not allowed. The product should be uniform in color. Various inclusions indicate the use of low-quality raw materials. It is especially worth paying attention to the ends of the pipes.

The products must be provided with certificates of quality and conformity. They are evidence that metal-plastic pipes for water supply are made in accordance with all requirements.

Don't try to save money. The cheaper the pipe, the lower its quality. Quite budget products have a short service life and low performance. They can fail even under normal conditions. Therefore, it is better to choose products from well-known manufacturers. Reinforced-plastic pipes combine the advantages of plastic and metal products. At the moment, they are the most practical option for the implementation of a water supply system.

Disappointment

Just 2-3 years after the massive appearance of new material on store shelves, the first negative reviews began to appear about it. They boiled down to complaints about leaks of compression (with union nuts and split rings) fittings on hot water and heating (see. Fittings for water supply of a private house). Usually the leak could be eliminated by tightening the nut; but often after a while it appeared again.

Typical Leak Location - Pipe-to-Fitting Connection

Note: multilayer metal-polymer pipes for cold water supply did not cause the slightest criticism from anyone and never. At a constant temperature of the working environment, no leaks occur, the water supply system serves the owner for a long time and flawlessly.

Metal-plastic pipe for cold water supply: there is no need to be afraid of leaks

The attitude towards metal-plastic has changed. Experienced plumbers began to recommend their customers to use steel pipes - black steel and more difficult to install galvanized.

Note: galvanized pipe should only be mounted on threaded connections. When welding in the seam area, the anti-corrosion coating completely burns out: steel melts at 1400 degrees, while zinc already evaporates at 900 degrees.

Installation of water pipes made of metal-plastic

Connection of pipes with fittings

For the installation of plumbing metal-plastic systems, special shaped elements are used - fittings for metal-plastic pipes. Using a variety of joints made of metal-plastic pipes, structures of various shapes and complexity can be mounted. A system of such pipes can be assembled and disassembled again.

There are three types of basic connections:

• detachable;
• compression;
• press fittings.

1. With the help of detachable fittings, metal-plastic water pipes can be undocked more than once with other fittings and devices, because these fittings contain threaded connections.
2. It is very difficult to undo the compression fitting, in case of serious need, you can simply change the compression ring to a new one.
3. The press fitting cannot be disassembled at all, the water supply metal-plastic pipes are pressed in once and for all.

Advice: it is necessary not to allow the embedding of compression and detachable fittings into concrete, since during operation it is necessary to have open access to them for regular maintenance.

Fitting

Installation of compression fittings does not require special equipment; you only need to have a few wrenches on hand. For press fittings, a special press tool is used, with the help of which a sleeve is used to crimp a metal-plastic pipe around the fitting.

Tools for installing plumbing pipes

Depending on the type of connection chosen for the installation of water pipes, the following tools are required:

• scissors for cutting metal-plastic pipes, pipe cutter or hacksaw for metal;
• calibrator;
• spring for bending pipes;
• spanners;
• press tool.

Manual press tool

How to install metal-plastic pipes of the water supply system

An important factor is the convenience and ease of installation of metal-plastic pipes in the water supply system.

Stages of installing metal-plastic water pipes:

1. Using a tape measure, measure the length of the future water supply and make a sketch of the drawing.
2. Decide on the number of required fittings: corners, couplings, adapters from one pipe diameter to another, and so on.
3. Cut the pipe to a certain size.
4. Insert the cut pipe as far as it will go into the required fitting.
5. Tighten the nut.

Tip: when tightening the nut, do not overdo it, because the thread may break or the fitting may break.

Advice: the installation of metal-plastic sewer and water pipes is recommended to be carried out at a temperature of at least 10 degrees Celsius.

Installation of water pipes made of metal-plastic

Decline

Almost completely metal-plastic pipes for hot water supply and heating have ceased to be used with the advent of polypropylene on the Russian market.

Polypropylene risers and water supply lines

Metal-polymer pipelines lost to him literally in everything:

• In the price of fittings and pipes;
• In the speed of installation;
• In the reliability of the connections (socket welding of polypropylene guaranteed strength, at least not losing the strength of a single piece of pipe). At the same time, maintenance-free connections could fit into grooves or screeds.

Metal-plastic has moved to the distant windows of plumbing stores and is gradually disappearing into oblivion. According to the author, it is absolutely undeserved.

Technical characteristics of metal-plastic pipes

Firstly, pipes for water supply and heating made of metal-plastic are distinguished by excellent strength, which is achieved by the correct sequence of layers of plastic and metal. Secondly, such pipes can withstand high pressure and temperature.

The following are specific specifications for different pipe diameters.

Installation errors

Let's think about why a metal-plastic pipe for water supply leaks. The reason is only and exclusively in the gross errors of installation.

How to

Compression fitting for metal-plastic is a herringbone fitting with one or two rubber o-rings seated in the grooves. It is these rubber rings that must ensure the sealing of the joint. The shape of the fitting is intended only to ensure reliable fixation of the pipe crimped with a split ring.

Compression fitting device

Rubber sealing rings are responsible for sealing.

Here is a step-by-step instruction on how to install the connection yourself:

How do

Now let's remember how newcomers in the field of installing these pipes collect heating and water supply from metal-plastic.

• For cutting, as a rule, a hacksaw for metal is used. The cut is only very approximately perpendicular to the pipe axis;
• Nobody removes the chamfer at the end. Moreover: even burrs from cutting are not always removed from the inner surface of the pipe;
• Calibration? No, you haven't heard. There is definitely no calibrator in the arsenal of a novice master. The oval pipe is pulled over the fitting with force and tightened to the stop with a split ring nut.

The result is fully consistent with the effort expended:

1. An oval pipe with an oblique cut and an unclean chamfer pulled over the fitting pulls the O-rings out of the grooves and pushes them towards the fitting body. In this case, the O-rings often break (the edge of the pipe, as we remember, is uneven and with burrs);
2. When tightening the union nut, the split ring squeezes the pipe on the fitting, ensuring the sealing of the connection due to the deformation of its inner shell;
3. When heated to 70-80 degrees or more, softened polyethylene is squeezed out of the gap between the fitting and the core;

Polyethylene melts at +120 degrees, but it begins to soften already at 80 ° C

1. Upon subsequent cooling and concomitant compression of all parts involved in the connection, the fitting leaks.

Sometimes, after two or three tightening of the union nut, the connection can be sealed by pressing the fitting with a soft aluminum core. At the same time, polyethylene is completely squeezed out from under the core, leaving it defenseless against electrochemical corrosion. Much more often, small irregularities on the surface of the core and the union interfere with sealing, and the connection continues to flow.

Irregularities and scratches in the fitting may interfere with the seal.

Features of the device of metal-plastic pipes

Reinforced-plastic pipes consist of three layers: outer and inner - polyethylene, intermediate - aluminum foil. The layers are bonded with a thermally stable adhesive.

Each of the layers of the metal-plastic pipe performs a separate function - the inner polyethylene acts as a carrier, the final mechanical strength of the structure depends on its thickness and density.

Foil has an insulating effect, it reduces the thermal conductivity of the line, thereby reducing the risk of condensation on its surface. The face layer of the outer polyethylene plays a decorative role and acts as a shell that protects the aluminum foil from damage.

Sizes and scope

Reinforced-plastic pipes are widely demanded both in individual household and industrial spheres. These products are used as:

• cold and hot water supply pipelines;
• heating system pipelines;
• pipelines for transportation of compressed air and hot steam;
• pipelines for the supply of liquid materials in the chemical, food and agricultural sectors.

Also, metal-plastic pipes are often used as protective and shielding jackets for laying wires and high-voltage cables.

The metal-plastic pipes used for water supply are presented on the market in the range of diameters 16-64 mm. In individual water supply and heating systems, the most popular diameters are 12-24 mm. From the factory, the products are delivered in coils 50-200 meters long.

Advantages and disadvantages, an overview of analogues

Polyethylene metal-plastic pipes have the following advantages:

1. Resistance to corrosion and, as a result, the absence of problems with permeability due to scale and third-party formations on the inner walls.
2. The plastic materials are completely anti-static.
3. Increased throughput. Due to the smooth inner surface, polyethylene products transport water 30% more efficiently than metal ones.
4. Durability - the service life, protected from mechanical damage, can be up to 50 years.
5. Minimum weight and ease of installation (no welding required, pipelines are formed using additional fittings);
6. Low thermal conductivity due to the presence of an insulating foil layer, which prevents the energy carrier from losing temperature during its transportation from the boiler to the radiators.
7. Polyethylene metal-plastic pipes have a perfectly smooth inner surface, which ensures the absence of circulating water noise.
8. Aesthetic appearance, no need for painting.

In addition to heating systems, metal-plastic pipes can be used for hot and cold water supply... The plastic materials used in their production are environmentally friendly and comply with all sanitary standards. They do not emit substances harmful to the human body when heated below the melting point (+120 degrees).

Construction of a metal-plastic pipe

An important disadvantage of metal-plastic products is their susceptibility to uneven linear expansion, due to the fact that the layers of foil, glue and polyethylene from which the pipe is made have different temperature coefficients.

In practice, the problem is as follows - when heated from the coolant, the contacting layers of the pipe increase in size, which leads to pipeline leaks at the fitting. The problem is eliminated by tightening the fitting, but after a while it reappears.

A series of subsequent pull-ups leads to the fact that the fitting begins to push through the foil layer and the slightest tightening can lead to its damage. For this reason, it is forbidden to lay polyethylene pipes inside concrete walls.

This problem is not typical for cold water pipelines. As an analogue for hot water supply and heating systems, polypropylene pipes can be considered (they do not belong to metal-plastic ones).

Unlike polyethylene products, such pipes are non-plastic (they cannot be bent, adapters are used for laying pipelines) and welding is used for joining, not fittings.

Also, it is impossible to allow water icing in metal-plastic products, which can cause their deformation and damage. If it is planned to operate the pipeline at subzero temperatures without draining the water, it is better to give preference to HDPE polyethylene pipes.

HDPE is the toughest polymer among all types of plastic materials. HDPE is characterized by an increased number of intermolecular compounds and, as a result, maximum density. High density HDPE provides:

• resistance to deformation during icing of the coolant;
• minimum vapor permeability;
• resistance to chemically aggressive substances;
• high mechanical strength.

You can distinguish HDPE pipes from plastic analogs by the ringing sound they make when they hit a solid object, while ordinary plastic products emit a dull sound. The main disadvantage of HDPE is unsuitability for hot water supply (the maximum allowable temperature for HDPE is +70 degrees).

Specifications

Consider the technical characteristics of a metal-plastic pipe of the most demanded diameter of 20 mm:

• wall thickness - 2.25 mm, thickness of the aluminum layer - 0.25 mm;
• weight of 1 running meter - 0.17 kg;
• coolant volume per 1 running meter - 0.200 l;
• thermal conductivity coefficient - 0.44 W / mK;
• internal surface roughness coefficient - 0.06;
• standard tensile strength - 2900 N;
• the minimum permissible bending radius is 80 mm (with manual bending) and 48 mm (using a pipe bender);
• vapor permeability - 0 g / m3.

Reinforced-plastic pipes and fittings
Rehau metal-plastic pipes used for hot water supply can be operated at a constant temperature of the coolant in +95 degrees, a short-term increase in temperature to +110 degrees.

The maximum working pressure that a foil-reinforced plastic pipe can withstand depends on its application:

• transportation of cold water (up to +20 degrees) - 94 MPa;
• hot water supply and heating systems (up to +90 degrees) - 10 MPa.

Do-it-yourself metal-plastic pipes connection (video)

How to repair

What to do if multilayer metal-polymer pipes for hot water supply have leaked at the fitting connection due to installation errors?

Fortunately, this type of connection is serviceable and can be dismantled:

1. Unscrew the union nut and slide the split ring;
2. Forcibly remove the pipe from the fitting;
3. Calibrate it and remove the inner chamfer;
4. Install the o-rings in the original grooves. If they are torn, replace the seals (or, if they are missing, the whole fitting);
5. Lubricate the fitting and reassemble the connection.

Press fittings

Metal-plastic pipes for water supply can be mounted not only on compression, but also on press fittings. What it is?

Structurally, such a fitting is distinguished by the absence of a thread, a split ring and a union nut. Their functions are performed by a stainless sleeve, which is crimped at the connection with mechanical or electrical pliers.

Let me introduce you: crimped press fittings

It is believed that this type of connections is much more reliable than compression ones and can be safely used for hot water supply and heating. And this is true, but not because of the magical properties of the cartridge case.

The fact is that crimping pliers are a rather expensive tool, and therefore they fall exclusively into the arsenal of professionals.Which, of course, do not save on buying much cheaper pipe cutters and calibrators.

Manual pliers for crimping press fittings on metal-plastic Valtec (16-32 mm). Retail price - 9500 rubles

Positive and negative qualities

Reinforced-plastic pipes have much more positive qualities than negative ones. But with proper installation and operation of pipes for hot water, these disadvantages will not lead to a violation of the integrity of the entire system or to its failures. Using high-quality heating equipment in combination with pipes, metal-plastic products will last a long time and will not create any problems. Due to the design features, metal-plastic pipes are endowed with a number of advantages that are not found in other types of water-supply products. They have the qualities of both metal and plastic, namely:

1. The pipe can be bent at a large angle, without the use of any tools or fixtures, that is, practically by hand.
2. Reinforced-plastic pipes have low thermal conductivity, which means that heat loss during operation is minimal.
3. The pipe is not subject to corrosion, scale or decay.
4. Maximum resistance to temperature fluctuations.
5. They give out minimal expansion due to the presence of the aluminum layer.
6. Metal-plastic has proven itself to work with both cold and hot water.
7. With the help of fittings and couplings, the installation of the system is simple, easy and quick.
8. The hot water temperature permissible for operation in systems reaches 95 ° Celsius, the maximum pressure is 10 atm., And the service life is about 50 years.
9. Low weight and noise level of water in the system.
10. The pipe is not affected by stray currents.
11. When working with reinforced-plastic pipes, you do not need complex assembly or cutting equipment.
12. Excellent appearance of pipes that does not need painting or any other processing.
13. Reinforced-plastic pipes are sealed and do not allow oxygen to pass through, therefore, heating equipment significantly increases its service life.
14. It is possible to use metal-plastic in combination with other materials (polypropylene, metal).

Hot and cold water supply installation diagram.

There are few significant negative qualities of metal-plastic pipes, but they are:

1. The high cost of couplings and fittings. Their price is due to the fact that they are made of a material that does not corrode. However, adapters are aesthetically pleasing and durable.
2. The second problem also applies to connections and temperature drops. If cold water was flowing through the system, and then hot water suddenly went, then this can lead to a small leak over time. But with timely maintenance, which consists in tightening the threaded connections, such troubles can be avoided.
3. The flow area of ​​the fitting is slightly less than the diameter of the pipe for which it is intended.
4. Direct sunlight on pipes is undesirable.
5. Reinforced-plastic pipes are afraid of mechanical damage.
6. There is a possibility of damage to the weld if water freezes inside the pipe.

Limitations

We have convincingly proved that with proper installation, metal-plastic can be used for heating and hot water supply. However, a number of restrictions still exist. Some of them are directly mentioned in the construction rules of SP 41-102-98, which regulate the installation and design of metal-plastic pipelines.

• The laying of metal-polymer heating pipes, if possible, is done hidden - in grooves, baseboards and niches;

Commentary: the requirement is related to the vulnerability of the shell and the core of the metal-plastic to mechanical damage. A strong blow can crush the pipe, or even break its tightness.

In the photo - the installation of an underfloor water heating system (underfloor heating) with metal-plastic. The pipe is laid in a heat-insulated screed

• With hidden laying, free access to connections and fittings must be maintained;
• Polymer-metal pipes cannot be used in systems with elevator units (that is, in most apartment buildings);

Commentary: in some operating modes, the elevator unit provides a direct supply of industrial water from a straight line of the heating main to the hot water supply and heating systems. The temperature in it at the peak of cold weather, according to the temperature schedule, reaches +150 degrees, which far exceeds the capabilities of metal-plastic.

Temperature regime of the heating main and its dependence on weather conditions

• In front of the metal-plastic pipeline for heating and hot water supply, shut-off valves should be installed (see Valves for water supply: types, purpose, nuances of selection), which allows you to quickly stop the supply of water or coolant in the event of an accident;
• If the coil of a metal-plastic pipe was stored at a negative temperature, then before rolling it must be kept in a heated room for at least a day;

Commentary: polyethylene remains elastic at low temperatures. However, water trapped in the pipes and crystallized there can damage the inner jacket or core during unwinding.

Small-diameter metal-plastic is supplied in coils for which storage in cold warehouses is permissible

• The bending radius of the pipe should not be less than five of its diameters. When bending, the walls should not be “folded”: it has a detrimental effect on the strength of the pipeline and reduces its throughput;

Commentary: at small bending radii, the pipe is bent in a steel spring put on it.

The spring allows you to bend the pipe with a small radius without damaging its core

• Reinforced-plastic is laid through building structures in a sleeve filled with an elastic material with a low coefficient of friction (for example, foamed polyethylene);

With horizontal laying of liners and spills, the fixing step should not exceed:

Clip for attaching paired metal-plastic water supply pipes to the wall

Characteristics of metal-plastic products

Distinctive characteristics of the line of this equipment are:

1. High strength. Reinforced-plastic pipes are able to withstand high internal pressure, retain their integrity in case of possible hydraulic shocks in the heating and water supply system.
2. Resistance to aggressive media. Corrosion resistant. They do not interact with most of the chemical compounds present in the circulating fluid (water supply, heating).
3. Light weight and easy installation.
4. Wide range of.
5. Affordable price range.
6. Long, warranty period of operation. The maximum service life of metal-plastic pipes for water supply (cold) is 15-25 years. The service life of metal-plastic pipes for heating and hot water supply depends on the temperature of the coolant. Sharp changes in temperature conditions negatively affect the properties of metal-plastic products. There is a violation of the sealing at the joints, reducing the trouble-free service life of the water supply system.
7. Possibility of laying in the ground, in a concrete base.

Avoid frequent bending of pipes.

Parameters of metal-plastic products