Butt-Fusion welding is a method for joining High Density Polyethylene (HDPE) pipe or fittings together where both ends are heated using a heating plate with constant temperature and pressure resulting in pipe and fittings to weld together homogeneously. Butt-Fusion welding technique is commonly used in gas pipelines and water distribution systems. Butt-Fusion welding is the most commonly used method of joining High Density Polyethylene (HDPE) pipes.

Butt-Fusion welding process of HDPE pipe consists of the following steps:

1. Preparation of pipe ends: Cut the pipe to the desired length and chamfer or clean both ends of the pipe using a trimmer or other applicable tools. Both pipe ends must be cleaned and dust free.
2. Pipe Alignment: The pipes are aligned using alignment clamps to ensure that both pipes are in the same level.
3. Heating the pipe using a heating plate:  Both ends of the pipe are heated using a heating plate at a constant temperature to ensure that the pipe ends are heated to the optimum level for welding.
4. Pipe welding: After the pipe ends are heated by the heating plate to the optimum temperature, the heating plate is removed and both ends of the pipe are welded together at constant pressure until cooled and joined together homogeneously.
5. Weld test : The process of testing welds is divided into destructive testing and non-destructive testing. Tensile and Bending tests will be performed to test the strength of the weld line in destructive testing. As for non-destructive testing, visual check of the pipe on weld seams and surface will be tested.

Butt-Fusion is the most widely used method for joining polyethylene pipes and has many advantages, including:

1. Robust and reliable: Butt-Fusion welding welds the pipe together homogeniously. This makes the welding strong and resistant to leakage. Butt-Fusion welding is the preferred method for welding pipes with high pressure and high flow applications.
2. No additional materials required: Unlike other piping methods, Butt-Fusion welding does not require additional materials such as adhesives or mechanical joints.
3. Ease of use: Butt-Fusion machine is easy to use and operated by trained professionals.
4. Cost-effective: Butt-Fusion welding is a cost-effective way to weld pipes as there is no additional materials required to join the pipes together.

However, Butt-Fusion also has its drawbacks, including:

1. Requires special heating tools: The heating tools used for Butt-Fusion, while it is easy to use, can be expensive to purchase. Therefore, it may be more convenient to rent.
2. Trained Professionals Required: Butt-Fusion welding should only be performed by trained and certified professionals to guarantee the quality of pipes and welding joints.