When various kinds of water and heat supply systems are equipped, there is a need to connect metal pipes with plastic ones. To solve this problem, you can use one of many options, but the main ones include the use of flanges and the method of threaded pairing.
The main types of compounds and their characteristics
If you decide to connect HDPE pipes with metal pipes, then it is important to familiarize yourself with the basic technologies of the work. With a threaded connection of metal pipes with HDPE of small diameter up to 40 mm, it is best to use fittings that have a thread for a metal pipe. At the same time, couplings are often used for these purposes. However, they are not used to connect HDPE pipes with metal. But for the joints of polypropylene elements among themselves, they will suit perfectly. To do this, you should purchase a smooth connecting element. In order to obtain reliable sealing of joints, flax fiber should be used, which is pre-processed in drying oil. This is true when assembling steel pipes. If we are talking about a flange connection where pipes of a larger diameter are used, then elements with a diameter of up to 600 mm can be mated. In this case, the twisting is carried out manually. Below we will consider the connection of polypropylene pipes using the thread method. Whereas the flange joint is best used in conjunction with polypropylene and polyethylene pipes. But it is worth noting that these compounds can be used for both varieties of products.
Threaded Fittings Applications
In order to install polypropylene pipes, which have metal parts in the form of filters, pipes, counters and mixers, fittings with a thread of the desired diameter can be used. This element will be located on one side, while on the other there should be a sleeve for soldering a plastic pipe. Thread for fittings can be external or internal. The connection of HDPE pipes with fittings is carried out according to the following procedure. First you need to unscrew the sleeve of the metal pipe in the place where you want to connect it to the plastic element. Otherwise, part of the steel pipe may be cut off, while the resulting edge must be treated with oil or solid oil, forming a new thread with the appropriate tool. At the next stage, the thread is wiped, a fum tape or tow is wound on it, the surface is lubricated with silicone. There should not be more than two turns, the edge of the tape should be guided along the thread during clamping. Without using a key, a press fitting should be screwed on to prevent cracking. If, after starting the system, water began to leak, then tighten the fitting.
Methodology
When the HDPE pipe is connected, the steel element can be paired with a fitting. Polypropylene elements will allow you to form different bends and turns in the system. The configuration of the fitting can also be changed, it must be warmed up for this with a building hair dryer, but the temperature should not be more than 140 °. Polypropylene will ignite if the temperature is above 350 °, which is why you should not allow the possibility of overheating. Polypropylene products expand and contract when exposed to temperature, so when using them to equip a heating system or supply hot water, it is necessary to install pipes under a layer of plaster. At the same time, the gap in the gates should be approximately one centimeter, and tubular insulation should be located around the tees and bends.
Flange application
The connection of pipes PND, PVC with metal can be carried out by means of flanges. In this case, it will be possible to obtain a detachable connection, for the implementation of which bushings for flanges are used. They are welded to the ends of the products. Otherwise, you can use patch flanges, which are made of metal. If during the work you will use the HDPE pipe, the methods for connecting this element to metal pipes may include the use of flanges. This technology is applicable if the pipe has steel components (valves, pumps can be attributed to this category). Among other things, a detachable connection is relevant when there is a need for disassembly of the pipeline during operation. Such a need arises during repair and cleaning. It is advisable to use the flange connection for pipes of large diameter. On sale you can find the so-called free-type flanges, they are based on collars and are most common when working with plastic pipes. Loose flanges can match the dimensions of the metal parts of the piping.
For reference
When connecting HDPE pipes with metal pipes with the help of flanges, it should be noted that the latter should be free of burrs and sharp elements. If present, polyethylene products may be damaged.
Specialist recommendations for flanged pipes
Above, loose flanges have been described, which are most often used for heavy and medium polyethylene products, the diameter of which does not exceed 150 mm. Among other things, such connecting elements can also be used for light pipes, while their diameter should not exceed a parameter of 300 mm. In order to increase the strength of the connection, you can use a straight shoulder with a conical transition. Loose flanges can be used to connect pipes with diameters in excess of 200 mm. The wedge joint, which is characteristic of curly flanges, can be used for pipes of any diameter.
Recommendations for work using flanges
When the PND pipe is connected to metal pipes using flanges, the pipe is cut off at the junction, while the cut should be as even as possible. A metal flange is put on the pipe, then a rubber gasket. Its release for a pipe cut should not be allowed, but the maximum inflow value is 10 mm. Slide the flange onto the gasket, and then make the connection using bolts. The bolts should be tightened evenly, the force is applied only until the moment you feel resistance. When working, it is necessary to be guided by the specification that is attached to the component parts.
Features of the connection of HDPE pipes
The connection of HDPE pipes is also carried out quite often in everyday life. To create a detachable connection, you can use flanges, which are the most common type of mount. This is because in the process there is no need to use welding. It will be most convenient to use water pipes, the diameters of which begin from a mark of 50 mm. If we are talking about a smaller diameter, then fittings or special clamps should be used, which are sometimes replaced by clamps. Flanges can be used to connect copper, cast iron or metal pipes with polyethylene. In order to connect HDPE pipes with compression fittings, it is necessary to properly prepare the pipeline. To do this, the plastic element is cut at a right angle. At the next stage of work, it is necessary to carry out the technology described above, however, in this case, two pipes will turn out to be plastic.
Features of connecting pipes from different materials
If you decide to connect the HDPE pipe with a metal pipe, then it is extremely not recommended to save trying to seal a plastic pipe with cement joints or by embossing technology. In the latter case, the plasticity of polyvinyl chloride or polyethylene will fail, since it will be impossible to achieve a tight connection. In addition, the pipelines are deformed. In other cases, we should recall the coefficient of thermal expansion of plastic. If hot water is released several times, the connection will simply loosen and lose its original tightness. If there is a need to connect the HDPE pipe with a metal pipe, but a seal was not found on sale, then the problem can be solved by using microporous rubber. From the old car carpet, it is necessary to cut a long narrow tape that can be wrapped around the joint by ramming the material inside with a blunt wide screwdriver.