Here are some factors that will influence the decision on whether to use butt fusion or electrofusion for jointing of PE pipes:
Pipe size - electrofusion is normally applicable to pipe sizes from 20mm to 710mm, whereas butt fusion is applicable to pipe sizes from 50mm to 2000mm.
Pipe material - electrofusion can be used to join different grades of the same material e.g. MDPE to HDPE.
Accessibility - electrofusion is particularly suited to installations where access is difficult, such as in trenches or around other pipes.
Pipe structure - whereas in butt fusion welding the pipes to be joined must have the same wall thickness, with electrofusion a difference in wall thickness can be accommodated. Electrofusion can also be used to join certain typesof multiple layer pipes, e.g. nylon lined polyethylene pipe for the conveyance of fuel.
Installation method - if the pipe is to be installed using a 'no-dig' technique such as directional drilling, then electrofusion cannot be used. Similarly, if the pipe is to be used as a close-fit lining in an existing pipeline,then butt fusion is the only viable technique