Electrofusion welding

Resistive heating of the coils melts small amounts of the pipe and fitting, and upon solidification, a joint is formed.

[1] Because of the consistency of the electrofusion welding process in creating strong joints, it is commonly employed for the construction and repair of gas-carrying pipelines.

Constant voltage is typically used for high pressure pipelines such as mains gas and water.

Coupler fittings contain two separate regions of coils, creating two distinct fusion zones during welding.

Installation of couplers and tapping tee fittings require slightly different procedures.

Electrofusion welding requires electrical current to be passed through the coils implanted in the fittings.

Energy input during the joining process is typically measured by controlling the time it takes for the current to pass through the fitting.

[4] A control box takes electrical power from a generator and converts it into an appropriate voltage and current for electrofusion joining.

The most common input voltage for electrofusion welding fittings is 39.5V, as it provides the best results without risking operator safety.

When a constant voltage machine is used, the value of the applied current slowly decreases throughout the welding process.

This increased electrical resistance causes a smaller current to be generated from the same voltage level as the process progresses.

After the current is shut off and cooling begins, the pressure slowly decreases until the joint is uniform temperature.

At larger gaps sufficient pressure cannot build during the fusion time, and the joint strength is low.

Despite the differences in flow rates, the final joint strength is generally consistent over a fairly wide range of pipe molecular weights.