Wales & West Utilities along with its long term contracting partner, Morrison Utility Services (MUS) has been successfully working on a highly innovative ‘Live’ Live Mains Insertion (LMI) project to replace approximately 4,200m of 12” cast iron with 250mm P.E in Wickwar, Bristol. The project included a record breaking insertion, for large diameter PE pipe, of 1,014m; a total of 84 x 12m sticks.
The Wickwar Road project was the first of its kind, worldwide, to be carried out using the LMI technique, developed by Steve Vick International, on larger diameter PE pipe and is part of Wales & West Utilities’ major 30 year gas mains replacement programme across Wales and the South West of England, which will provide a safe and dependable gas network for the future.
The LMI technique is a safe, fast and efficient method of replacing old cast iron mains with new P.E. pipe, without interrupting customers’ gas supplies. The major benefits provided by LMI meant the technique was the obvious choice for MUS.
The idea of using the LMI technique for PE above 180mm, which comes in lengths rather than coils, was discussed a number of years ago and successful trials have since been undertaken. In order to approve this method, a proposal was taken to the Wales & West Utilities innovation committee and Paul Breakey, Project Leader discussed the feasibility with Steve Vick International. It was agreed in principle that LMI could be carried out on larger pipes. After a number of successful trials and completion of G23 documentation and deviation paperwork, Wales & West Utilities approved the system in late 2018.
Live Mains Insertion
Live Mains Insertion is similar to normal insertion of polyethylene pipe (PE) into an old cast iron main with one important difference. By using a special gland box and a live head on the PE, the old main is kept live throughout the insertion process and the new PE is gassed up to maintain supplies to customers.
Once insertion is complete, the main is kept live to supply customers with gas via the annular space until it is operationally convenient to transfer the services to the new PE main.
A further benefit of live mains insertion over dead is that only one excavation needs to be open during the insertion process, reducing traffic management requirements. Operators consider this a major consideration with the cost implications of the new Traffic Management Act.
Wickwar Road Gas Mains Replacement Project – September to December 2018
With a scheduled completion deadline of December 2018, a twelve week schedule of works was drawn up which involved a one way fed live insert with an estimated ten insertions over 4.2km. This averaged 350 meters a week.
The most ambitious of these insertions was a record breaking 1,014 metres in one continuous length, which took just under three hours to insert using the Steve Vick large Pipe Handler. The Steve Vick Large Pipe Handler range is available for PE diameters from 250mm up to 1,200mm. The complete laying of the pipe and abandonment for this section took a total of two weeks. Up until that point, the project team had inserted a maximum of 630 metres in a single push.
The project involved pushing a 250mm PE pipe inside a 12” CI main, leaving an annulus of 200mm. The PE pipe had a ‘live head’ attached that was designed and manufactured by MUS sub-contractor Thompson Utilities and involved adapting a dome head using a specialised mesh gauze which was positioned inside the head to stop the rust, common in larger pipes, entering the PE pipe. Following the air pressure test, a calculated number of holes were drilled into the dome head to allow the gas from the network to flow into the 250mm PE. Careful calculations were then made on the flow of gas to ensure there was enough gas in the annular space to provide the consumers of Wickwar, a small village outside Chipping Sodbury, with an uninterrupted gas supply throughout the insertion process.
In total 9 innovative tools were used, saving time, money and effort over conventional practices and improving safety and disruption. The tools included; SVI Macaw Pipe Crackers, SVI Large Diameter Pipe Handler, Soil Picks, Profuse Peelable Pipe, System 1 Twin Bagtube, Crawler Cameras, PE flowstopping, As-laid Drawing Capture, Re-usable Supatees.
In total, cost savings of approximately £500,000 were made utilizing LMI over Open Cut on this single project alone. Disruption was also reduced by 100m per week, Open Cut would have taken 40 weeks to complete but LMI took just 11, allowing huge cost savings to be made.
Paul Breakey, Project Leader at Wales & West Utilities, commented: “The use of innovation on standard jobs can be a win-win for the customer, our contract partners, and us. Wickwar Road demonstrates how it pays to innovate, facilitating a safer, quicker, and less disruptive scheme while delivering value for money.”
The project was completed a week ahead of schedule on the 14th December 2018. Onsite support and consumables were provided by Steve Vick International.