Steve Vick International’s Contract Service teams have renewed forty 1¼”, 2” and 4” live gas risers in multi storey buildings in the centre of Glasgow without the need to decommission the services whilst the work was in progress.
Using their Live Gas Riser Transfer technique, SVI were able to save Scottish Gas Networks tens of thousands of pounds compared with carrying out the project the traditional way by providing a new riser on the building exterior. The saving on not having to use scaffolding alone covered the cost of the entire project.
Live Riser Transfer allows a section of old service entering under the building to be partly renewed or transferred to a new main without first throwing it dead. It is hugely beneficial in multi-storey, multi-occupation housing as it avoids the need to gain access to each dwelling to turn off and relight the gas and avoids disruption to consumers’ supplies.
The properties involved included two three-3 storey buildings over a ground level car park and three 25-storey high-rise blocks of flats. As part of SGN’s mains replacement programme, the feeder main to the properties was being renewed which required the risers (10 x 2”, 24 x 1¼” and 6 x 4”) to be transferred to the new PE main. The work was carried out between November 2014 and January 2015.
Using a combination of under pressure tees, under pressure drilling equipment and a flanged valve, SVI’s technique allows a new service to be pieced in and commissioned. In order to abandon the old section of riser, an angled under pressure tee is fitted below the new service and is drilled to allow a FOAMBAG™ to be installed.
A conventional flow-stopping operation is performed outside the building by the Gas Distribution Network to enable the redundant section to be purged and tested. The entire abandoned section of service may then be filled with foam to ensure safety in the future. The steel riser below the new supply is cut and capped and a permanent prop is installed to support the weight of vertical risers.
For safety, the under pressure tee and the live end of the old service are fitted with collars which are filled with fire retardant material.
In Glasgow, a separate SVI Contract Service team arrived following completion of the Live Riser Transfers to carry out Live Stub End Abandonment on the redundant short sections of gas main which remained in the ground outside the building. This technique allows an excavation to be made in a convenient location, remote from the main, and the foaming off operation is performed via fill tubes with the aid of a CCTV camera. The entire length of unwanted main is filled up to the tee junction with the parent main to prevent risk of future leakage.
George McDonald, SGN’s Team Manager on the Glasgow project, said, “Using a traditional method of riser renewal would have generated the problems associated with gaining access to each flat for re-lighting. Using the Steve Vick Live Riser Transfer method we were able to significantly reduce costs and save time. We were very pleased with how straightforward the Live Riser Transfer procedure was and how quickly it was completed.”