Gas Mains Replaced Using Live Mains Insertion In St. Peter-port – Guernsey

Guernsey Gas has carried out the first live insertion of a gas main on the island for two decades. The project involved renewing 126 metre of cast iron main in Le Pollet in the centre of St. Peter-Port.

A technician from Steve Vick International Ltd, the company which supplies equipment for the technique, was on site to offer help and advice. Only one excavation was required for the insertion, a major advantage in the narrow streets of St. Peter-Port.

First a bypass was set up to maintain the low pressure gas supply to customers and flow stopping bags were inserted between the bags. A section of the old main (which varied from 6” diameter for the first 40 metres to 8” for the remainder) was then cut out and the special Lyontec™ gland box fitted to the end of the cut out main.

A pneumatic pipe pushing machine was installed in the excavation and a ‘live’ head, designed with holes to allow for the flow of gas, was fitted to the end of the 90mm PE. This was then pushed into the gland box until the plastic membrane within was pierced. Gas was then allowed to flow into the coil of PE on the pipe coil trailer. Once 100% gas was achieved the flow stopping bags were removed from the main and the PE pushed to the end of the 126 metre section. This operation took approximately 25 minutes and at no time were customers off gas.

The PE was then squeezed off and cut out ready for connection into the existing main. The gland box was left in position acting as an end seal. The bypass was closed, with customers receiving their supply from gas in the annular space supplied via the ‘live’ head. Finally, the excavation was backfilled.

There were 13 services off the main, mainly commercial and retail customers including several restaurants. Guernsey Gas transferred the services over the following few weeks at a time convenient for the businesses. They excavated down to the services in groups of three or four, injecting a Steve Vick International Insertion Seal foam kit to seal off the annular space before connecting the services to the new PE main.

Phil Jones, Distribution Manager with Guernsey Gas, said, “We decided to use the live mains insertion technique as the streets are very narrow in St. Peter-Port and it meant we could minimise disruption to shops and businesses. It was also very useful to be able to schedule the transfer of services to fit in with our commercial customers’ requirements.

“Since this operation at the end of February we have carried out another live mains insertion involving 190 metres of 63mm into 4” and have scheduled a further 200 metres of 75mm into 4”, added Phil.