Metal in modern pipelines is used infrequently. Most communications today are assembled from durable plastic, most often polypropylene. Naturally, the methods of connecting water and sewer polypropylene pipes are different from conventional welding.
Installation of polypropylene products
There are two main types of installation of plastic pipes:
- one-piece welded: fusion of parts under the influence of high temperatures using a welding machine of a special design; due to the lack of gaps at the docking points, this method is considered the most reliable; it is ideal for 16-40 mm pipes; the disadvantages include the impossibility of temporary dismantling;
- a variation of the previous type of connection is the so-called cold (adhesive) welding, a method in which plastic is not melted, but dissolved using special adhesive compositions; but this method is applicable only for pipelines intended for supplying cold water;
- detachable (fitting): by means of intermediate elements — adapters; the method is applicable mainly for pairing thin-walled products and pipes of small diameter, as well as joining pipes from different materials: propylene with polyethylene, propylene with metal; to reinforce the mating points, use Teflon tape or sealant.
The latter type of installation is quite acceptable only for pipes through which cold water will be supplied. After all, when heated, as a result of thermal expansion, a gap may form between the mating parts, and, as a result, leakage. Therefore, for connecting pipelines with hot water and installing heating systems, the welded method is considered more reliable.
Fixed welded joints, in turn, are divided into:
- butt: do not require the use of additional parts; welding is carried out «pipe to pipe»; a similar method is applicable for joining parts of large diameter, and only from polyethylene; for polypropylene, a similar method is not used; plus it requires special expensive equipment; since it is not suitable for working at home, so we will not dwell on it in detail;
- bell-shaped with the use of adapter fittings (muff welding); the outer side of the pipe and the inner surface of the fitting are subject to melting; it is this method that is used for the installation of hot water pipelines and heating systems.
Advice! For a system of underfloor heating and cold water distribution, it is advisable to take pipes marked PN-10. Products of larger diameter PN-16 will be needed to assemble the heating system. When using parts PN-20 and -25, only welding is used.
Creating a Permanent Weld Joint
How to connect polypropylene pipes (PP) to each other? The ideal option is welding. This installation method, in which the molten polypropylene of the pipe and fitting is mixed at the molecular level, is often referred to as diffuse welding. The result is a coherent structure.
To create welded joints, you need to stock up on the following tools:
- pipe cutter for perfectly even cuts or a hacksaw;
- welding machine: in everyday life it is called a soldering iron for polypropylene;
- trimmer or nozzle on a drill for stripping reinforcement;
- a regular knife or tool for chamfering (edge) slices;
- building level;
Diffusion welding in stages
The process of joining by welding at home is simple. Most importantly, work accurately and accurately. In order to adapt to the operation of the apparatus and accurately maintain the time of plastic melting, at first it is better to practice on a small piece of polypropylene pipe.
So, we tell you how to solder plastic:
- The soldering iron must be placed on a horizontal, flat surface.
- The ends of the pipes are cleaned and trimmed so that a cut is obtained exactly at 90 °. With the help of trimming, burrs are removed, as well as reinforcement that interferes with the mating of the segments.
- After stripping, the ends are degreased with acetone.
- They are put on special nozzles of the welding machine, heated to a certain temperature (it is indicated in the instructions and depends on the diameter of a particular pipe).
- Nozzles of the desired diameter are pre-selected and attached to the welding machine. This will require a little effort. The part on which the fitting is put on is called the mandrel. The nozzle on which the end of the pipe is attached is a sleeve.
- After heating the parts for a few seconds, the pipe and fitting are removed. This must be done at the same time, with both hands.
- The end of the heated pipe must be immediately inserted into the fitting until it stops and firmly fixed by hand in this position for a few seconds. It is forbidden to displace or screw the length into the fitting. Docking should be done only in a straight line. The fixation and cooling time of the plastic is indicated in the table — an appendix to the instructions.
Advice! To obtain a strong connection, pipes and fittings of the same thickness and diameter are used. It is highly undesirable to weld products from different manufacturers — the material must be compatible in its chemical properties.
Basic Welding Mistakes
Connections can become loose as a result of the following errors:
- plastic pollution or moisture ingress: foreign inclusions getting into the heated plastic leads to its deformation; water, in the process of heating, quickly turns into steam, drops of which, mixing with plastic, lead to its weakening;
- incorrectly selected temperature: if it is not high enough, the seam will be weakened and leak over time; overheating of the plastic can lead to the loss of its shape and the formation of sagging, which will impede the normal patency of the pipeline;
- insufficient exposure time until the polypropylene is completely solidified, while distortion is possible;
- the nozzle of the heated pipe into the fitting is not completely, as a result of which a hollow section with a reduced wall thickness is formed; the strength of the seam in this place decreases, and even a small increase in pressure can lead to leakage;
- a similar defect is also formed with uneven cuts or the presence of burrs that have not been removed, which lead to the formation of voids;
- excessive effort when connecting parts and their displacement; as a result of this defect, plastic deposits are formed that interfere with the passage of water;
- poor-quality stripping of the foil from the intermediate layer; even the ingress of a small piece leads to a decrease in the patency of the pipeline.
Another way to securely connect polypropylene pipes. It turns out to be as solid as the seams obtained as a result of diffuse welding. Cold welding can be used when mounting parts of almost any diameter, both large and small. However, since the adhesive can soften at elevated temperatures, this method is only applicable to cold water or sewer systems.
- After marking, cutting pipes, and such stripping and trimming, the interfaces are cleaned of dirt and degreased with acetone.
- Glue is more convenient to apply with a gun or brush. The composition must be distributed evenly over the intended surface.
- Next, the pipe and fitting are pressed tightly against each other for a short time (it is indicated in the instructions). As a rule, 20-30 seconds are enough to thicken the composition.
- Details must be carefully, trying not to shift, set aside. Although the setting time of the compositions is 15-60 minutes, it is allowed to subject the seam to loads only after the final polymerization, which lasts at least a day. It is not allowed to move or separate parts before the expiration of this time.
Advice! When buying glue for cold welding, carefully read the instructions. In some cases, it will require mixing the two components to make it. In case of violation of the correct proportions, the adhesive properties of the drug may decrease.
Detachable fitting connection
You do not know how to connect a HDPE (polyethylene) pipe with a polypropylene one? Take advantage of this method. It is suitable for interfacing and other materials, as well as the installation of small diameter pipes.
Docking by means of detachable fittings is convenient — at any time the connection can be disassembled, cleaned or replaced. No special tools are needed to create it — just scissors for cutting polypropylene or a hacksaw for metal and a set of wrenches.
Let’s describe the process of creating a detachable connection in stages:
- At one end we attach a crimp nut. A split ring should also be located here. Moreover, its edge should be located 1 mm from the edge (cut).
- We join it with the second pipe and fix it on the fitting.
- We wrap the crimp nut with a wrench.
Docking of plastic pipes with metal elements
Pairing polypropylene with other materials by welding is technically impossible. In these cases, only a flange connection is used. For the installation of polypropylene products with different types of mixers, counters and other devices, the adapters of which are made of steel, it is necessary to select special fittings equipped with two types of fasteners — internal or external thread and soldering coupling.
The connection of polypropylene with steel by means of fittings is carried out as follows:
- A metal element requiring docking is treated with oil or grease. Next, a thread is cut on it. Depending on the type of fitting, it can be internal or external.
- You can seal the thread with tow or fum tape. Tow is better to additionally process with silicone.
- We screw on the fitting.
- To its other end we bring a polypropylene pipe heated with a soldering iron.
Metal-plastic and polypropylene
How to securely connect a metal-plastic pipe with a polypropylene one? There are three main ways to create such lines:
- by means of couplings and a pair of fittings designed for specific types of pipes;
- flanges with metal washers;
- with bi-directional polyethylene sleeves and fittings: the most reliable and proven method used for heating systems.
The fastening of the pipes is done by welding or by threading. Fittings for metal-plastic are made only of metal. Flanges are not used in such systems. Additional sealing in the joint is provided by a fum tape.