Steve Vick News
Live Mains Insertion around the country19 May 2008
Three of the gas distribution companies have recently completed large diameter gas mains renewal projects using the Live Mains Insertion technique to minimise disruption in town centres.
In Bournemouth, Southern Gas Networks carried out the replacement of a low pressure 14” cast iron main with 250mm PE in Christchurch Road. The 200 metre section of main ran under the city’s principle pedestrianised shopping area which is lined with shops, cafes and restaurants with residential properties above. Not only was it vital to minimise disruption for the retailers, shoppers and delivery vehicles, but also the area is block paved, requiring excavation to be kept to a minimum to avoid high reinstatement costs.
Live mains insertion of large diameter mains, typically with PE of 250mm and above, is similar to normal insertion of PE into an old iron main with one important difference – by using a special Steve Vick International gland box, the old main is kept live throughout the insertion process to maintain gas supplies to customers. Once insertion is complete, the main is still kept live to supply customers via the annular space until it is operationally convenient to gas up the PE and transfer the services to the new main.
Equipment for carrying out Live Mains Insertion, including the Lyontech™ gland box, reversible stand pipes and pipe pushing machines together with consumables such as Insertion Seal and End Seal foam kits, are supplied by Steve Vick International.
Bournemouth
In Bournemouth, the insertion process was carried out at the end of 2007 and the project was safely left over the busy Christmas period in order not to disrupt business in the city centre. In January 2008, the team returned to connect the services. As Colin Osborne, Team Manager for SGN, explained,
“This was a section of very old cast iron main and we were unsure of the number of services connected to it. It could have been hundreds which is one of the reasons why we planned to use Live Mains Insertion so that we did not leave shops and restaurants without gas for any length of time. In addition, we only needed very minimum excavation. As it happened”, continued Colin, “there were 63mm feeder mains in place so there were not too many services to connect.”
One of the difficulties of the project was that, given the extremely busy nature of the area, it was impossible to string out the 250mm PE so it had to be inserted in three or four lengths and butt fused, halting the insertion process each time. The total length of main renewed in this section was 200 metres and the insertion process was carried out in a few hours. Peter Balson, Planning Engineer with Southern Gas comments, “The job did go extremely well and the Chamber of Trade were as pleased as punch with the lack of disruption to business which was largely a result of having used the Live Mains Insertion technique.”
Leicester
In Leicester, National Grid, with their Alliance partner Amec, are using Live Mains Insertion in an on-going project to renew a 12” cast iron main under the A47 road out of the city. With its mixture of residential and commercial properties there are a total of 240 services off the main which is being inserted with 250mm Profuse.
John Orton, Construction Engineer with National Grid, said, “We are using the Live Mains Insertion technique as it causes far less disruption for traffic, pedestrians, businesses and residents. It means consumers stay on gas until the last moment when their service is being connected to the new main. This usually means they are only off gas for half an hour or so.”
By restricting excavation to an absolute minimum, inserting the old main with PE rather than digging up the road in the traditional way is obviously a major advantage in keeping traffic flowing. “With heavy traffic, a narrow pavement and restricted access to the main because of other utilities, mains insertion was an obvious choice for this project,” says John, “and doing it ‘live’ meant that, with the large number of services, we could schedule the work without the pressure of having customers off gas.”
Unlike in Bournemouth where service connections were carried out at a later stage, National Grid insert a section then foam off the annular space and immediately connect the services.
Durham
Live Mains Insertion has been a little used technique in the North of England until now but it has proved to be a winner in Durham where some 200 metres of ductile main were renewed in February in the heart of the city by United Utilities and Balfour Beatty on behalf of Northern Gas Networks.
Barry Watson of United Utilities said that around 200 metres of PE was pushed under the full length of Silver Street from the Market Place to the far side of Framewelgate Bridge. As much of the area is under ancient cobbles, minimising excavation was a major priority.
The 10” ductile main was inserted with 213mm PE, one of the newer thin walled pipe sizes (SDR21). Unlike cast iron which can be easily smashed to gain access to the inserted pipe, ductile iron has to be cut using a special window cutter. The equipment supplier and contracts engineer, Steve Vick International, carried out several window cutting operations during project.
United Utilities and Balfour Beatty used a Steve Vick International pipe pushing machine to speed up insertion of the PE. This hydraulically operated machine pushes in the PE at a rate of up to 4 metres per minute. The advantage of pushing in the pipe, rather than winching, is that the pipe can be pulled out again if an obstacle is met with. Dave Little of Northern Gas Networks said, “I am impressed with the pushing machine. We managed to insert 215 metres in one push and negotiate at least three kick joints.”
The company says that it plans to use Live Mains Insertion to speed up many more mains replacement jobs across its region in 2008.
With projects due to commence shortly in North London and West Midlands, large diameter Live Mains Insertion is truly becoming a national success.