Marshall, Hepburn, Netherwood
# 1995 Edinburgh
The adoption of polyethylene as a pipe material by both the gas and water indusmes has undoubtedly led to several sigruf~cant economic and operational advantages. The development of narrow trenching techniques and insertion refurbishment methods only became viable once a complete fusion jointed polyethylene system was available.
The ability to heat fuse polyethylene is a major advantage of a polyethylene pipe system. Socket, saddle and bun fusion techniques have been developed and proven over several years. Electrofusion, in which heat is supplied elecuically through a resistance coil embedded in a socket or saddle fitting is being used in increasing numbers by the UK water industry. In concept, the elecmfusion process has potential advantages to offer the pipe engineer, both in terms of the ease with which the jointing can be accomplished and the possible safety and integrity of the jointing process.
Problems have however been encountered with the introduction of the system into the water indusny. Fittings have been failing more and more frequently. In most cases the contractor has been blamed for their failure, but this has become less acceptable and in some cases hard to believe since a number of failures have occurred where there has been only minor site practice deficiencies.
Manufacturers change designs on the basis of their own research and development and they assess performance by means of tests included in international standards for assessing fitting and bond strength['] which are relatively insensitive to major design changes. It is thus not only difficult to assess whether one type of design is better than another and but also it is also questionable as to whether the tests are representative of service conditions for a water main, and of whether information gleaned from such tests relates to actual service performance.
With such a background, a consortium of the UK Water Utilities (Plastics Pipes Systems Group), have sponsored investigations of the processes involved in electrofusion, the mechanisms of failure and the development of new test methods for incorporation into standards.