Connection of HDPE pipes to a metal pipe: features, practical recommendations and feedback

When different kinds of water and heat supply systems are equipped, there is a need to connect metal pipes to plastic pipes. To solve this problem, one of a variety of options can be used, however, the main ones involve the use of flanges and the threading method.

Basic types of connections and their characteristics

If you decide to connect HDPE pipes to metal pipes, it is important to familiarize yourself with the basic technologies of the work. With 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, clutches are often used for these purposes. They do not, however, be used to connect HDPE pipes to metal. But for the joints of polypropylene elements, one can do the best. To do this, you should purchase a smooth connecting element. In order to obtain reliable sealing of joints, you should use flax fiber, which is pre-treated in linseed oil. This is true when assembling steel pipes. If we are talking about a flanged connection where pipes of a larger diameter are used, then it is possible to match elements whose diameter reaches 600 mm. In this case, the twisting is done manually. Below we will consider the connection of polypropylene pipes using the threading method. While the flange joint is better used together with polypropylene and polyethylene pipes. But it should be noted that these compounds can be used for both types of products.

Threaded fittings

In order to install polypropylene pipes that have metal parts in the form of filters, pipes, meters and mixers, fittings with threaded diameters can be used. This element will be located on one side, while on the other there must be a coupling for soldering the plastic pipe. The thread for the fittings can be external or internal. The connection of HDPE pipes with fittings is carried out according to the following procedure. First it is necessary to unscrew the clutch of the metal pipe in the place where it should be connected to the plastic element. Otherwise, a part of the steel pipe may be cut off, whereas the resulting edge must be treated with oil or solidol, forming a new thread with the help of a suitable tool. At the next stage, the thread is wiped, the foil tape or tow is wound on it, the surface is smeared with silicone. The turns should not be more than two, the edge of the tape with the clamp must be guided along the thread. Without the use of a key, a press fitting must be wound to avoid cracking. If the water starts to leak after the start of the system, then the fitting should be tightened.

Methods of work

When the HDPE pipe is connected, the steel element can be paired with a fitting. Polypropylene elements will allow to form various bends and turns in the system. The configuration of the fitting can also be changed, it needs to be heated with a construction hair dryer for this, but the temperature should not exceed 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 the heating system or the supply of hot water, it is necessary to install pipes under the layer of plaster. In this case, the gap in the stitches should be approximately one centimeter, around the tees and branches, tubular insulation should be located.

Application of flanges

The connection of HDPE pipes, PVC and metal pipes 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 flange sleeves are used. They are welded to the ends of the products. Otherwise, it is possible to use overhead flanges, which are made of metal. If during the operation you use the HDPE pipe, the ways of connecting this element to the metal pipes can provide for the use of flanges. This technology is applicable if the pipe has steel components (this category includes valves, pumps). Among other things, the detachable connection is relevant when there is a need for disassembly of the pipeline during operation. This need arises during repair and cleaning. The flange connection is suitable for large diameter pipes. On sale you can find so-called flanges of a free type, they rely on the collars and are most common when working with plastic pipes. Free flanges can correspond to the dimensions of the metal parts of the pipelines.

For reference

When the connection of HDPE pipes to metal ones is made with the help of flanges, it should be noted that there should be no burrs and sharp elements on the latter. If they are present, polyethylene products may be damaged.

Advice from a specialist in connecting pipes with flanges

Above we described the free flanges, which are most often used for heavy and medium-sized polyethylene products, the diameter of which does not exceed 150 mm. Among other things, such connecting elements can be used for light pipes, moreover their diameter should not exceed a parameter of 300 mm. In order to achieve an increase in the strength of the joint, you can use a straight-end collar with a cone transition. Free flanges can be used for connecting pipes whose diameters exceed 200 mm. The wedge joint, which is characteristic of the figure flanges, can be used for pipes of any diameter.

Recommendations for work with flanges

When the HDPE pipe is connected to the metal with the help of flanges, the pipe is cut off at the connection point, and the cut must be as flat as possible. A metal flange is put on the pipe, then a rubber gasket. Its outlet beyond the pipe cut must not be allowed, but the maximum value of the fill is 10 mm. The flange should be pushed onto the gasket, and then make the connection using bolts. Bolts should be tightened evenly, the force is applied only until you feel resistance. At work it is necessary to be guided by the specification, which is attached to the component parts.

Features of the connection of HDPE pipes

The connection of HDPE pipes is carried out in everyday life too often. To create a detachable connection, you can use flanges, which are the most common type of attachment. This is due to the fact that in the process of work there is no need to use welding. It will be most convenient to use water pipes, whose diameters start from a mark of 50 mm. If it is a smaller diameter, then use fittings or special clamps, which are sometimes replaced with clamps. Flanges can be used to connect copper, cast iron or metal pipes with polyethylene. In order to connect the 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 above-described technology, however in this case two pipes will turn out to be plastic ones.

Features of connecting pipes from different materials

If you decide to connect the HDPE pipe to a metal pipe, it is highly discouraged to save, trying to compact the plastic pipe with sealing joints with cement or using coining technology. In the latter case, plasticity of polyvinyl chloride or polyethylene will fail, since a tight connection can not be achieved. In addition, the pipelines are deformed. In other cases, we should recall the coefficient of thermal expansion of plastic. If several times the hot water is released, the connection will simply loosen up and lose its original tightness. If it is necessary to connect the HDPE pipe to a metal pipe, but the sealant could not be found on the market, then the problem can be solved by using a microporous rubber. From an old carpet, you need to cut a long narrow ribbon, which you can wrap the joint, ramming the material inside with a blunt wide screwdriver.

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