Under what circumstances are the different methods used?
Butt fusion can be used for jointing pipes and fittings 63mm diameter and larger. However it is most commonly used for larger diameter pipes. Butt fusion jointing is equally suited to both coiled and straight pipe lengths. Only pipes and fittings of the same nominal diameter may be butt fused.
Butt fusion can be used in new installations using traditional open cut trenching techniques. Additionally due to the low profile of the butt joint it is ideal for use in trenchless technology installations, sliplining, pipe bursting, directional drilling, etc.
Butt fusion can also be used to fabricate a range of fittings, bends, tees, reducers, etc.
Electrofusion is most commonly used for jointing pipes up to 250mm diameter but there is no technical upper limit. It is nevertheless most commonly used for smaller diameter pipes because the cost of fittings increases with diameter. Electrofusion is equally suited to both coiled and straight pipe lengths, and can be used to joint pipes of different nominal diameters and SDR's using suitable fittings.
Electrofusion is most commonly used in conventional open cut trenching installation, and in repair works. It is also used for adding new services to existing PE mains by means of saddle fittings or tees. It is less well suited to trenchless installation or rehabilitation methods because the fittings protrude on the outside of the pipe.
Electrofusion fittings are available in a range of forms; they may be straight connectors, bends, tees, stop ends, reducers, saddle fittings and repair fittings.
Mechanical assembly is used for jointing where neither fusion method is suitable. Most commonly this is when PE and other pipe materials are being connected, or when PE pipe is connected to valves or similar appurtenances made from other materials.
Mechanical fittings used in gas networks will have an internal support to avoid creep of the pipe which can lead to leakage. Most end uses in the gas industry specify mechanical fittings without elastomeric seals, tightness is achieved by compression of the PE pipe to the fitting body or stiffener.