Welding of pipe branches, tees and Y-branches

What is different about a branch

A straight joint requires two pipes meeting in line. A branch requires one pipe to meet the side of another – either as a T-piece, Y-branch, cross or as a saddle on a larger pipe. The welding principle is the same as in butt welding, but the equipment and preparation are different.

The branch must be held securely at the correct angle while the main pipe is clamped. Therefore, branch equipment typically features a wider clamping range, more clamps and a frame capable of supporting both pipes. This makes the machine heavy, which is the main practical limitation: branch equipment is rarely something you carry around.

Working ranges and weight

Branch equipment is available in a few size classes: small machines for branches on thinner pipes and large machines for branches on main pipes up to around Ø400 with a branch up to around Ø315. Straight pipes and segmented bends typically cover the machine's full range, whereas T-pieces, Y-branches and crosses have a slightly smaller range because space is required for the clamps on both sides.

The weight typically lies between 550 and 650 kg for large machines, and the space requirement in operating position is around 1.2 x 1.7 x 1.6 m. In addition, the machine must stand level and on a firm foundation because the weight of both pipes rests on the frame.

Preparation: geometry is the hardest part

For a straight joint, it is sufficient to ensure that the ends are flat and parallel. For a branch, both the side of the main pipe and the end face of the branch must be prepared: the main pipe must have a clean, flat seat where the branch meets the wall, and the branch must be cut so that it meets with a full contact surface at the desired angle.

Use the template or protractor designed for the equipment, and check the angle before inserting the heating element. A branch that is misaligned cannot be adjusted after welding – it must be cut out.

With thick-walled pipes and large diameters, heat distribution in the branch differs from that in a straight pipe. Follow the equipment manufacturer's table for heating and cooling times; it may differ from the table for straight joints, and the manufacturer's table takes precedence if it is more specific.

Space, power supply and safety

Large branch machines require 400 V 3P with a dedicated fuse and a level substrate capable of supporting the machine and pipes. The heating element and planer have their own power ratings, so the total load must be taken into account when planning the workplace.

Set up barriers around the work area: the frame is heavy, the pipes can tilt, and the heating element is hot. When working in the trench, the excavation must be secured against collapse, and the machine must be positioned so that it cannot slip.

If the branch is to be installed on an existing pressurised line, squeezing off and an approved working procedure are required – this is a different task from the welding itself and must be planned in coordination with the utility company.

When the branch should be made as a saddle instead

For small branches on large main pipes, it is often easier to use an electrofusion saddle fitting or a mechanical branch fitting rather than clamping the entire main pipe in a branch machine. This requires less space and fewer clamps, but the fitting must match the pipe material and SDR.

If there are many branches on the same project or the branches are large, branch equipment using butt fusion welding is the most economical option and provides the most consistent quality.