The main welding techniques used in installations 

Pipe welding is a crucial stage in the installation of plastic piping systems, as it affects the leak-tightness, durability and resilience of the entire system. In practice, three main techniques are used: thermal, electrofusion and butt welding. Each is based on the controlled heating of the material, but differs in terms of equipment requirements, the process sequence and typical areas of application. An understanding of these differences makes it easier to select the appropriate method for the operating conditions, pipe diameters and the complexity of the installation. 

Thermal welding — a simple technique with great potential 

Thermal welding utilises external heating, which enables pipe ends to be joined without the need for additional fittings. Once the material has been prepared, the components are heated to their melting point and then joined under pressure. The result is a cohesive structure that performs well in installations exposed to variable operating conditions. This technique is particularly suitable for systems made of PP-R (random copolymer polypropylene) and PE (polyethylene) due to the chemical resistance of these materials. 

Accuracy is key during the work. Incorrect heating parameters can weaken the inner layer, so the operator should monitor the time, pressure and temperature. Thermal welding is popular in water and heating systems, where repeatability is important and there is no need to use many different types of fittings. Although the procedure is relatively straightforward, technical supervision and experience have an impact on the final quality of the joint. 

Electrothermal welding — precision based on fittings 

Electro-resistance welding involves the use of fittings fitted with a resistance wire. Once the fitting has been placed on the pipes, the control unit supplies a current of a specified value, causing both the interior of the fitting and the outer surface of the material to heat up. This method allows for precise control of the parameters, as the welding machines read data from the manufacturer’s code and automatically select the power supply duration. 

This method is particularly suitable for installations with complex geometry. A large number of branches, changes in direction or work within existing networks require a solution that allows operations to be carried out in areas with limited working space. Electrofusion welding is therefore used in narrow trenches, in building structures and when commissioning new sections. It is most commonly used in PE pipelines, where the ability to join pipes of different diameters and the repeatability of the joints produced are key factors. 

Given the nature of the technology, it is worth noting a few factors that determine the quality of the joint. This requires preparation appropriate to the fitting used; in practice, therefore, a few simple rules are followed: 

  • the surface of the material must be cleaned mechanically, 
  • the components must be secured in place whilst they are heating up, 
  • The heat sealer should operate in accordance with the manufacturer’s specifications, 
  • The connection requires a full cooling time. 

These measures improve the durability of the weld, particularly when work is carried out in the field. Checking that the material has been properly prepared and that the fitting is securely positioned reduces the risk of installation errors, which is particularly important in water and gas installations. 

Butt welding — the solution for long sections 

Butt welding involves joining the ends of pipes that have been heated using a heating plate. Once the correct temperature has been reached, the operator joins the components under a single axial pressure, and after cooling, a uniform weld is formed with properties similar to those of the material from which the pipe is made. This technique is used for large diameters, in long linear sections and where a low number of additional fittings is required. It is one of the most durable methods of joining polyethylene pipes. 

During butt welding, the precision of the alignment and the quality of surface preparation are crucial. The pipes must be precisely aligned, as even slight deviations can affect the geometry of the finished joint. In practice, a centring frame, end-processing tools and a constant-temperature heating plate are used. Such equipment requires adequate workspace, which is why this method is not suitable for hard-to-reach areas. 

This solution is often chosen for work involving large diameters. The fact that fittings are not required reduces the cost of installing long sections of pipework, whilst the stable nature of the process ensures consistent quality of the joints throughout the various stages of installation. For this reason, butt welding is used in transmission pipelines, where resistance to loads and operation over long linear sections are key considerations. 

How do you choose the right method? 

Each technique has different applications, so the choice should be based on the operating conditions and the scope of the installation. Thermal welding is suitable for water and heating systems where PP-R or PE pipes are used. The electrofusion method facilitates the installation of systems with complex geometries and allows work to be carried out in areas with restricted access. Butt fusion is best suited to large diameters and the installation of long, straight sections of pipework. In every case, the correct operating parameters and the contractor’s experience are crucial, as they affect the quality of the joint and the durability of the entire system 

FAQ: 

1. Which pipes are best suited to thermal welding? 
Thermal fusion is most suitable for random copolymer polypropylene (PP-R) and polyethylene (PE) pipes. Both materials respond uniformly to heating and allow durable joints to be formed without the use of fittings. They are also chosen for water and heating systems because they withstand fluctuating pressures and elevated operating temperatures well. 

2. What pipe diameters are most commonly joined using the butt-welding method? 
Butt welding is primarily used for larger-diameter pipes, where other techniques become less practical. In many projects, it is used from DN63 upwards, as below this size it is more convenient to use electrofusion welding. In transmission systems, joints are also made for diameters above DN160, where butt welding provides the best geometric stability and load-bearing capacity. Large diameters also benefit from this technique due to the absence of costs associated with purchasing fittings. It is also important for contractors that the process allows the structural uniformity to be maintained over long sections of pipeline. As a result, the butt-welding method is the predominant solution for projects involving extensive pipeline routes. 

3. Can butt welding be carried out at low temperatures? 
It is possible, but it requires adherence to stricter rules for preparing the work area. During such work, protective covers are used to shield against wind and precipitation, as an unstable environment causes the material to cool down rapidly. The heating time often needs to be extended, following the recommendations given in the equipment manufacturers’ tables. It is also important to monitor the operation of the heating plate, as fluctuations in its temperature affect the quality of the plastic’s softening. On exceptionally cold days, it may be sensible to suspend the installation or move it to a location offering more predictable conditions. 

4. How do you select the heating parameters for thermal welding? 
The heating parameters are selected based on the diameter of the component, the wall thickness and the type of plastic. Manufacturers provide sets of values which serve as a reference for the operator and make it easier to adapt the process to the operating conditions. Before starting the assembly, it is worth assessing the condition of the surface and checking the cleanliness of the heater, as variations in heating can lead to localised weaknesses. On colder days, it may be necessary to extend the heating time or adjust the clamping force. Maintaining constant pressure during joining helps to ensure uniform weld geometry around the entire circumference. 

5. Can every PE installation be repaired using electrofusion welding? 
Electrofusion welding enables a wide range of repairs to be carried out, particularly where access is restricted. However, its effectiveness depends on the condition of the material — significant deformation, permanent bends or a lack of space to securely position the fitting rule out this method. In such cases, other solutions are used, including re-joining the pipes end-to-end after cutting out the damaged section. It is therefore crucial to check whether the geometry of the pipeline allows for the safe installation of an electrofusion fitting.