As part of the push to ensure all gas replacement works are completed before the Olympics arrive in London, National Grid Gas called upon Steve Vick International’s Special Contracts Team to carry out a Live Gas Main Stub End Abandonment on a 12” low pressure cast iron main, in the heart of Piccadilly.
Where a new 315mm PE pipe had been laid, the existing 12” cast iron main needed to be fully abandoned to remove the risk of any possible gas flowing back into the pipe. However, the tee piece at which the main connected to the parent main was located in the middle of the highly congested A4 dual carriage way, opposite Hyde Park in Piccadilly.
Stub End Abandonment Live
A technique developed by Steve Vick International, Stub End Abandonment, is a cost effective solution ideal for use where it’s impractical to disconnect a redundant L.P main directly at its connection with the parent main. This is often because the tee piece is located under a busy junction or in a sensitive area, where disruption caused by the work would be unacceptable. Using the well proven FOAMBAGTM technique, in conjunction with CCTV equipment it is possible to excavate the stub end in a non-sensitive location, and abandon it under gas free conditions from the point of the main connection to the cap end, up to a maximum distance of 50 metres.
The existing live 12” main was accessed via an excavation in a less problematic area, where the camera was able to enter the main via a WASK base and 2” drilling. The footage confirmed that the neck of the parent main was 30 metres away, in the middle of the A4. The FOAMBAGTM was then remotely inserted via the same gland system using umbilical tubing, and with the aid of the camera, it was located at the exact point of the tee piece. Via the tubing, the FOAMBAGTM was then filled with expanding resin foam, pumped in using an injection machine. Once the FOAMBAGTM had cured, the camera system was removed and the isolated 12” main was vented and checked for any build-up of gas pressure, then a metallic cap was fitted.
To complete the procedure and permanently abandon the main, the 30metre section was filled with foam, using a fill tube inserted via the primary bag hole. The end of the tube was then pushed inside the main and the plug was replaced. Wayne Hall, National Grid Gas states ‘’The Stub End Abandonment method was the perfect solution to abandon the main without digging down. As this area of Piccadilly gives access to some of the most prestigious hotels and offices in London, it was never an option to close the road and deny access to these premises , not to mention the huge financial implications and time scales leading up to the Olympic Games”
One of the key benefits when using the Stub End Abandonment technique is the substantial cost savings. The alternative often results in expensive carriageway excavations, traffic management systems, reinstatement costs and guarantees, as well as the long period of time to carry out the work. Digging in the middle of the road also brings significant health and safety risks to operatives having to work in busy carriage ways. Stub End Abandonment is approved for use on low pressure. Systems from 3” to 12” in diameter and lengths of up to 50metres.
In connection with OFGEM implementing a new three tier replacement schedule from 2013; which could avoid actively replacing large diameter mains, Sean Noonan, Operations Director, Steve Vick International explains that “potentially, there will be a large number of stub-ends that require abandoning following the new replacement policy. The technique has been around for over 15 years, which is often referred to as Remote Foam bag or Long Stop , and while it is well known amongst Operatives and Managers, the Planners are not always aware of the technique and its benefits”. Since this has become apparent, we’ve carried out several training sessions either introducing or refreshing teams within planning departments across the networks”.
For more information on our Special Contract Services, please visit the website or contact us direct.
Date published – 14th June 2012