Information

Pipes made of low-pressure polyethylene are welded with socket and butt machines, as well as with the help of electric couplings. To avoid leaks, it is important to use quality soldering equipment. But a lot also depends on the experience of the welder himself. In this article, we will look at the key mistakes that beginners make when welding. This will save you time and money, and help you quickly learn how to create a quality connection.

Mistakes in preparing a pipe for welding
The tightness of the joint and the strength of the connection depend on the correct preparation of the HDPE pipe for welding. Often a number of mistakes are made when soldering precisely at the preparatory stage.

Bad sweep
Cleaning the outer layer is necessary for electrofusion welding of HDPE pipes or soldering with a socket soldering iron. Polyethylene is oxidized from the external environment, due to which the outer layer becomes refractory. If it is not cleaned mechanically, local non-heating is possible, which will lead to leakage (especially in systems with high pressure from 6 atm).

Use a mechanical scraper to avoid soldering errors. It is suitable for pipes with a diameter of 16 - 200 mm. Polyethylene pipes of large circles can be more difficult to rotate along the axis, so special tools are used to remove the top layer without rotating the workpiece.

Another mistake when manually cleaning from oxide is the insufficient length of the removal of the outer layer. Therefore, you first need to measure the depth of the coupling and measure this value on the pipe with a margin of 5 - 10 mm.

Oily dirty surface
The end of the HDPE pipe can be covered with sand, dirt, debris accumulated during transportation, storage, loading or unloading. There are traces of technical fluids on the plastic. With any welding method, a common mistake is to forget to degrease the surface. In the case of soldering with a butt joint, it is enough to wipe the butt and 20 mm around it with an alcohol wipe. For socket soldering or the electrofusion method, the entire length is wiped with alcohol, going inside the fitting and a little further for a margin. Without such a preparatory measure, inclusions in the form of debris and fat prevent the reliable connection of polyethylene at the molecular level.

Bad fix
The next mistake that is made when soldering pipes is the lack of fixation or weak fixation of the workpieces. In the case of butt welding, a centralizer is used, where crescents of different thicknesses achieve alignment of the structure. The electrofusion method uses belt clamps for large diameters and metal clamps with thread for small circles. This ensures a smooth line of the pipeline, prevents distortions, leaks.

uneven trimming
A crookedly cut HDPE pipe is another mistake in butt welding. If you cut a polyethylene blank with a chain saw, a jigsaw, a circular saw, a grinder, the edge will inevitably be uneven. When reducing the ends, even taking into account melting up to 5 mm, fistulas are possible. Therefore, to prevent errors, the edges must be processed with a trimmer designed for the corresponding diameter of the HDPE pipe.

Incorrect position of the coupling
A common mistake when brazing low-density polyethylene pipes is the incorrect location of the coupling. This leads to a small area of welding between the two sides, which can result in leakage or weak fixation of the structure.

Some fittings have a stop that limits the movement of the pipe. When assembling before soldering, it is required to push the workpiece to the end. In other couplings, there is no stop, so the error lies in the uneven distribution of the pipe edges inside the coupling - one went too far, and the second only by 20-30 mm. To prevent such an oversight, you must:

Measure the clutch with a tape measure.
Divide the length by two.
Use a light marker to mark the obtained value on each edge of the pipe.
Put the coupling on the ends and push it up to the marks.
Welding with the machine can be started after making sure that both marks are near the edges of the coupling. It is especially important to apply clearly visible landmarks when inserting a repair part into an existing communication. To insert a piece of pipe to be replaced, the coupling has to be completely pushed onto one of the edges, and then returned to the opposite side.

Various SDRs
At the stage of purchasing parts for soldering pipes, you can make a mistake by choosing pipes and fittings with different SDR values. The abbreviation means the ratio of the diameter of the HDPE pipe to the thickness of its wall. For example, two workpieces of the same outer diameter can have different thicknesses - 4 and 15 mm. Accordingly, it will not be possible to connect them qualitatively. If you choose a coupling with a smaller SDR than a pipe, then the workpieces cannot even be inserted one into the other.

Mistakes in pipe welding itself
In the process of welding itself or when brazing HDPE pipes, there are other common mistakes that should be avoided. Among them:

Wrong heating time. Tables of the optimal heating time, depending on the wall thickness and pipe diameter, are attached to the instructions for the device itself. If the heat supply is insufficient, the polyethylene simply will not solder together, which will lead to the destruction of the connection. Overheating is also considered a mistake when welding, because then the ends are strongly melted and deformed.
Insufficient cooling time. Some HDPE pipe welding machines automatically calculate the cool-down time from the coupling barcode. With butt welding, data must be entered manually, so it is important not to make a mistake. Insufficient cooling time can lead to a decrease in the strength of the joint and deformations.
Wrong pressure calculation. In butt soldering, the pressure to bring the sides together is calculated by the formula. Lack of pressing force weakens the strength of the seam. Excess - creates unnecessary influxes, reduces the length of the pipe, which then may not be enough to connect.