Niagara Mohawk, a National Grid company, recently undertook a gas mains insertion project in West Albany, upstate New York, which was carried out ‘live’ using a special technique pioneered in the United Kingdom. ‘Live’ mains insertion allows customers to remain on gas throughout the insertion process. The final stage of transferring the old services to the new PE main can then be scheduled to suit individual homeowners.
Lori Brown and David Zielinkski from Niagara Mohawk made a fact-finding visit to the United Kingdom and witnessed live mains insertion being carried out in the West Midlands area by Transco, the UK operator of the gas network. The technique is widely used in the UK, where it was developed during the 1980’s by British Gas (now National Grid Transco) with sealant technology by Steve Vick International.
It was decided that the project in Albany was an ideal opportunity to try out the technique. It involved the insertion of 4” polyethylene (PE) pipe into a two-way fed 6” cast iron main for a distance of 347 feet and was part of a larger mains renewal programme in the neighborhood involving seven insertions in total. The British company supplying the insertion equipment and foam sealants, Steve Vick International, was on hand to offer technical advice. Peter James from Steve Vick’s distributor in the USA, PLCS Inc of Mount Laurel, NJ, was also in attendance.
In the UK it is usual for a perforated head to be attached to the end of the PE as it is inserted to allow gas to pass between the PE and the annulus. However, Niagara Mohawk adopted a slightly different technique, fitting a ‘dead’ or closed head on the PE. This enabled the operators to gas up the entire string of PE, using bottled gas, to 1psi and test it prior to insertion.
With one excavation open, flow stopping bags were installed either side of the intended insertion point, a valve was closed and the main was cut out. The Steve Vick International pneumatic pipe pushing machine was then positioned in the trench and a Lyontec™ gland box fitted to the end of the main to be inserted. The other end of the main was temporarily capped off.
Another aspect of this live mains insertion was the use of a tracer wire, which was attached to the leading end of the PE. This would later enable Niagara Mohawk to locate the main easily.
Using the pushing machine, the PE pipe, with tracer wire attached, was pushed into the Lyontec™ gland box, piercing the gas-tight membrane. The flowstopping bags were then deflated and removed from the main. Monitoring the pressure continuously, the PE was pushed into the main, taking approximately half an hour to insert the 347 feet. The new PE was then tied into the existing low pressure system, which was running at 8” w.g. The gland box was left attached to the end of the inserted main as a seal. The excavation was then backfilled.
Transferring the services
The following day was spent in the workshop where Steve Vick International carried out demonstrations of the annulus sealing techniques to be used in the next stage of the project – transferring individual services.
Five services were connected in one operation, although the system would have allowed individual transfers on separate days had this been necessary. The process involved excavating down to the main, which was located using the tracer wire, at each dwelling. At the service point furthest from the inserted end of the PE, the main was drilled under ‘no gas’ conditions to allow the injection of Insertion Seal foam into the annulus. The twopart resin foam kit was mixed on site and injected using a special applicator gun. The foam expanded to seal the annular space allowing the main to be cut out. The five services, which had previously been renewed with PE, were then connected to the new PE main. A tailored fabric End Seal, also injected with expanding resin foam, was fitted to seal the gap between the cut out main and the inserted PE.
Neil Proudman, Vice President Gas Delivery for Niagara Mohawk, says, “Due to this project’s success, we’ve proved that this technology is transportable to the US. We now intend to expand its use across our mains replacement program, benefiting the company through cost savings, daily commuters by less road works and our customers by minimising service disruption. Everyone wins.”
Date published – 4th May 2005