Saddle welding: branch connection on a pressurized main pipe

What a saddle is used for

A saddle is used when making a branch connection on an existing main pipe without cutting it. The assembly consists of a plastic component that follows the curvature of the pipe, which is welded onto the pipe surface. Afterwards, a hole is drilled through the saddle and the pipe wall so that the branch is connected to the main pipe.

The method is used for service lines in water and gas networks, for branch connections in industrial settings, and for smaller inlets on existing pipelines. The advantage is that the main pipe can remain in place, and the work can be carried out in a confined space.

Two methods for welding the saddle

In heated tool saddle welding, the pipe surface and the underside of the saddle are heated against a mating heating element. The saddle is then placed into position and held under pressure until the material has solidified. The tool features a clamp or clamping device that holds the saddle securely in place and applies the necessary pressure.

In electrofusion welding, the saddle is a fitting with an integrated heating wire. It is clamped in place, connected to the control unit, and the cycle runs according to the fitting's parameters. Electrofusion saddles are simpler to control, but require a power supply on site and a fitting that matches the pipe diameter and SDR.

With both methods, the pipe surface is critical. Oxide layers, dirt, and moisture must be removed, and the surface must be dry and sufficiently rough to ensure adhesion. On jacketed pipes, the jacket must be removed in the welding zone in accordance with the manufacturer's instructions.

On small pipes with sufficient space to insert a tee, the branch connection can instead be made as a standard joint using socket fusion. This requires taking the pipeline out of service and cutting it.

When working with PVC-U, different conditions apply: lower heating element temperature, short changeover time, and extraction. Read how in butt welding of PVC.

Pipe preparation and fit

The pipe is peeled or scraped clean in the area the saddle is to cover, and cleaned with spirit. The saddle must fit tightly against the pipe across its entire surface. If the pipe is oval or has a bulge, it must be rerounded or moved to a better location; otherwise, the joint will leak at the edge.

The saddle and pipe must be made of the same material, and the dimensions must match. A saddle for PE100 cannot simply be used on a PE80 pipe with a different wall thickness, and a saddle for SDR 11 does not fit an SDR 17 pipe. Always verify the combination in the supplier's table.

The pipe must be supported so that it does not move during heating and cooling. For pressurized pipelines, follow the supplier's and utility company's instructions for squeeze-off and pressure conditions.

Drilling and completion

Drilling is only carried out once the joint has reached its full cooling time. The drill bit must have the diameter required by the branch, and drilling must be performed through both the saddle and the pipe wall without damaging the opposite pipe wall. Use a pilot drill or a drilling machine capable of limiting penetration.

After drilling, check that swarf has been removed and that the branch is unobstructed. Swarf inside the pipeline can subsequently lodge in valves and fittings.

Inspection and documentation

Inspection consists of a visual check of the bead all the way around, a pressure test of the branch, and documentation of the welding cycle. For heated tool welding, the temperature, heating time, and cooling time are recorded; for electrofusion welding, the control unit's log is saved.

For larger installations, a sample is taken from a corresponding saddle for tensile or bend testing, see DVS 2203 and testing. Branch connections on main pipes are typically documented with position, date, operator, and welding cycle, see welding log and documentation.