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Before the welding sequence, heating and cooling times and fusion pressures should be noted for the specific pipe diameter and written down for quick reference during the welding cycle. Some machines have all the relevant tables on them for convenience. A timer or stopwatch should be available for accurate timing.

The heatproof bag should be removed from the hotplate, and the temperature should be checked using a digital thermometer and surface probe.

It is good practice to complete a dummy weld before undertaking actual welding. This is to ensure the surface area of the hotplate in contact with the pipe ends is totally clean of any dust particles or other contaminants.

Place the hotplate between the pipe ends, ensuring that it is properly located and square to the pipe faces. Move the pipes into contact with the surface applying an axial force. The force should be applied smoothly making sure that the required pressure is not exceeded. The force needs to be held securely, allowing the formation of a bead of molten material around the pipe.

The bead needs to be even around the pipe circumference, on both sides of the hotplate. This is the 'bead up' phase of the process.

The means of applying the force will vary with the type of equipment. On certain types of machine the force will be applied by mechanical means using a spring loaded mechanism with the force being maintained by a locking screw. On other types of equipment, hydraulic rams are used with the pressure maintained by switching valves in the hydraulic power pack.

When the required bead has been achieved, the pressure is reduced for the heat soak phase. The pipes rest on the hot plate which allows the heat to permeate the material, reducing the possibility of cold welds.

This time will vary subject to pipe diameter and wall thickness, therefore manufacturers recommended times should be used.

When this phase is completed, the pipe faces are moved away from the hotplate as smoothly as possible to ensure that none of the molten bead sticks to the surface and the hotplate is removed. The pipes are then brought together as smoothly and quickly as possible to minimise the possibility of temperature drop, taking care not to exceed the required force.

The welding/cooling phase begins when the required force has been achieved. The weld force should be maintained throughout this phase, to ensure maximum weld strength

On completion of the cooling time, the pressure can be reduced to zero, and the pipe removed from the clamps. The finished weld can now be visually inspected for uniformity and alignment.

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