Welding of HDPE pipes: butt-joint and electrofusion, detachable and one-piece installation methods

HDPE pipes are widely used for laying sewerage, gas and water pipelines. They are chosen for ease of installation, durability and other benefits. They can be used for both pressurized and non-pressurized systems such as sewerage. For installation, the HDPE welding method is often used. The advantage of this technology is that even a person who has no experience of such work can weld pipes with his own hands.

Installation features

Polyethylene pipes are practical and reliable. They are used both in manufacturing and in housing construction. For manufacturing, polyethylene is used - a material that is resistant to aggressive media. Due to this property, HDPE pipes are often used for the installation of various pipelines. For this purpose, products with a diameter of 20 to 1200 mm are used.

They are connected in two ways:

• detachable, with the help of sockets and flanges;
• one-piece, with the use of welding.

The connection method is selected depending on the conditions in which the pipeline will operate.

If it is mounted to transfer a medium under pressure, for example, water or gas, then welded joints are used, which are characterized by increased strength and tightness. Pipes through which the liquid will move independently, for example, sewer pipes, are connected using fittings and flanges. This connection is easier to make.

One-piece connections

By welding, you can reliably connect polyethylene pipes. This method allows you to obtain strong and tight seams that are resistant to aggressive environments.

The welded joint has the following advantages:

• it retains the original flexibility of the pipeline;
• does not affect its strength;
• allows you to get a tight seam that does not lend itself to aggressive environments.

Products can be connected by butt welding of HDPE pipes or using electrofusion couplings. Before starting welding, regardless of which connection method is chosen, make the following training:

• purchase pipes and fasteners (fittings and connecting elements), as well as clamps and reduction liners of the corresponding diameter;
• equip a working platform for welding;
• process the ends.

The operability of the welding equipment is checked. This is done as follows:

• inspect the units of the welding machine, check the health of the electrical wires and the degree of sharpening of the end knives;
• fuel the electric generator;
• parts of equipment are cleaned of contamination, surfaces are degreased using a solvent;
• check the oil level in the equipment hydraulic system, treat all rubbing parts with special compounds;
• check the instrumentation.

Butt welding

Butt joint is used for pipes with a diameter of 50 mm. It requires a butt welder. During operation, the end pieces heat up and join under pressure. At the same time, polyethylene melts and creates a strong seam, which in its properties is not inferior to a solid product.

This type of connection is rather complicated. It requires professional equipment to guarantee high quality seams. The person doing this work must have sufficient qualifications. Butt welding has the following advantages:

1. No heavy equipment is required for work.
2. It can be produced by one or two people.
3. It is an economical process as the power consumption of the HDPE welding machine is much less than that of the steel pipe welding machine. Such equipment can be purchased at a hardware store or rented from assembly firms.

For butt welding, products with a wall thickness of no more than 4.5 mm, made of the same grade of polyethylene and having the same diameter, are suitable. They must also have the same SDR, which is equal to the ratio of the inner diameter to the pipe wall thickness. Welding is performed in the following order:

1. Check products, their ovality and SDR.
2. They clean the dirt from the surface, remove chips from the ends. If necessary, align the edges with an electric cutter that cuts the pipes at an angle of 90 º.
3. Both pipes are fixed at a distance of about 4 centimeters between the ends.
4. With the help of a welding machine, a layer of polyethylene is straightened at the ends.
5. The temperature at the ends is raised using a heater. The material is heated to deep layers, the process of its melting begins.
6. After the polyethylene has warmed up for a certain time, which depends on its thickness and the diameter of the products, the heating part of the welding machine is carefully removed. The pipes will fit together. The time between removing the heating element and connecting the ends should be kept to a minimum.
7. To create the required pressure, a machine with a displacer is used.
8. After the materials have cooled down, an airtight layer is formed on the pipes - a collar.

It is important not to make mistakes in the technological process, otherwise the layer will turn out to be crooked and insufficiently sealed. When machining, the edges of the pipes must not be moved more than 10% of the wall thickness.

Welding is carried out at an ambient temperature not lower than +15 ºC. The pipeline is operated at temperatures from -15 to + 45 ºС.

Using electrofusion couplings

The electric coupling is a part made of polyethylene with electric spirals implanted into the body. Manufacturers produce couplings for pipes of various diameters. For straight welding, products of a straight shape are used; for other designs, electrofusion tees, saddle branches and other parts are suitable.

The joints created by electrofusion welding of HDPE pipes are capable of withstanding pressures up to 16 atmospheres. But they are more expensive than butt-welded ones. This is due to the fact that each of them requires the purchase of an electrofusion coupling. The work is done as follows:

1. Thoroughly clean the surface of the pipes, clean their ends.
2. The inner surface of the coupling is degreased.
3. The edges of the pipes are inserted into the sleeve and the whole structure is fixed.
4. She is energized.
5. The coupling and end parts melt. When they solidify, they form a monolithic connection. The sleeve remains over the seam.

It is important that the structure remains stationary during heating and cooling, for which it must be firmly fixed.

Welding using an electrofusion coupling is used in cases where several connections are required. This can be a tie-in of an additional branch into an already installed pipeline. For welding a large number of pipes, it is better to use the butt method.

The advantage of electrofusion welding of HDPE pipes is that the installation process is quick and easy, and the result is a high-quality connection. Welding can be done by hand, even without proper training. In this way, products with a wall thickness of less than 4.5 mm can be joined.

Layout with fittings

The detachable method of connection is not as reliable as the welded one, but it also has its advantages.

These include:

1. Profitability. The workflow does not require special equipment and tools.
2. Versatility. The connection can be installed where welding cannot be used, such as underwater.
3. Fast installation. The pipeline can be assembled as soon as possible.

For reliable and proper operation of the pipeline, it is necessary to ensure a high-quality pipe connection. The seams made by HDPE welding are distinguished by the greatest strength and tightness. It can be produced by a butt joint or by using electrofusion couplings.