Butt fusion involves the simultaneous heating of the ends of two pipe/fitting components that to be joined, until a molten state is attained on each contact surface.
The two surfaces are brought together under controlled pressure for a specific cooling time and a homogeneous fusion joint is formed. The resultant joint is fully resistant to end loads and has comparable performance under pressure to the pipe itself.
An electrical heater plate is used to enhance the temperature of the pipe ends to the targeted fusion temperature.
Butt-fusion can be used to connect both PE80 and PE100 materials for pipe sizes of 90mm and above of the same SDR or pressure.
The butt fusion welding machines used to weld PE pipes have controls to ensure the welding parameters are strictly followed. The elements below are important:
· heater plate temperature
· interface pressure
· bead width
· heat soak time
· changeover time
Control of these is necessary to ensure success of the weld . The field conditions under which PE pipe is welded have a great effect on the strength of the joint. In order to achieve a satisfactory weld , the following three factors need to be focused:
· Cleanliness: contamination can ruin joints
· Technique: Most of PE pipe systems require people performing butt welding .
· Correctly designed equipment with proper maintenance: Correct welding temperatures, welding procedures and pipe facing tools must be maintained in good condition.
The resulting joint is as strong as the original pipe and can withstand all the loads applied during installation and operation.
During the fusion process internal and external ‘weld beads' are formed. Techniques have been developed to minimize the size of the beads, however as they do not add anything to the overall strength they may be safely removed if required. The removed weld beads can be inspected as part of a quality control programme.