Following research in its laboratories and implementation on experimental sites, GAZ DE FRANCE authorized polyethylene service pipes to be used in 1974 and polyethylene pipelines to he used on its network in 1979. At the same time, it was decided to authorize electrofusion as the only assembly method, with the intention to develop the corresponding technique gradually as the possibilities and need evolved in accordance with GAZ DE FRANCE specifications. In recent years, rust new extensions and renovations of the GAZ DE FRANCE network have applied a coherent "Electrowelded Polyethylene System" (E.P.S.), thus gradually converting the distribution network to polyethylene.
After describing the main characteristics and advantages of this "Electrowelded Polyethylene System" gas technique, the authors emphasize two salient features of the system
use of very long pipes (several hundred meters) both for renovation and new extensions of the network.
The drum-wound polyethylene tubes can be laid by a trencher at a speed of up to 300 meters per hour for laying network extensions. For renovations, lengths of 80, 100 or more meters can be inserted in the former low pressure pipeline requiring only minimum excavation work.
It should be noted that the "Electrowelded Polyethylene System" comprises all the necessary tools : tube cutters, positioners, scrapers, welding set, drums, road-trailers, drum-carriers, trenchers, winches and pulling accessories. It also includes all the accessories of the network and the repair and build-up techniques and equipment.
Implementation of the E.P.S. gas technology is of direct assistance in converting the GAZ DE FRANCE former low pressure gas distribution network to the "medium pressure B" 4 bar distribution pressure enabling the customers to be supplied both more reliably and at lower cost.
Since the advent of natural gas, the industry in FRANCE ton expanded considerably, leading to rapid development of transmission and distribution networks. The gas transmission network supplies the offtake stations of the consumer centres at a pressure of 70 bar. A distribution network feeds the gas at 19 bar (medium pressure C) either to district pressure regulation stations supplying the distribution networks operating at 4 bar, to pressure regulating stations serving industrial customers at 4 bars, or again directly serving industrial customers at 19 bar.
It should be noted that the former cast-iron distribution networks operating at a pressure of 20 to 25 millibar are generally supplied from the 4 bar distribution network through pressure regulating stations.
The remainder of this paper will essentially deal with the distribution network operating at 4 bar, known in FRANCE as the "medium pressure B network" and which, as we shall see, is developing thanks to the use of polyethylene, in place of the networks operating at a pressure of 20 to 25 millibar, known as the "low pressure network".