NWL cleaning of 14.964km of 36

This involved design input, procurement of materials, installation and testing of works covering approximately 70km of mains each year over a five year contract period valued at around £15 million.

Adverse weather severely limited the time available to carry out the project and so teams worked every day for 16 weeks, leaving no down time available to resolve any equipment failure or unexpected problems.

The accelerated plan involved installation of two 900mm line valves and twin washout arrangements, to reduce the length of main out of commission and allow phased chlorination, charging and commissioning.

Variations in diameter of 50mm were encountered on dowel sections and pipe ends so our Project Engineering Manager developed a device to re-shape the pipe, allowing standard 935mm couplings to be used on almost all of the 28 access dowel sections. This delivered a significant cost saving and operational efficiency, as bulk orders of coupling could be made before dowels were cut.

Blistering of the internal bitumen lining was identified via closed circuit television. This was repaired using Water Research Council (WRC) approved resin, a process which involved men entering the pipe after a safe method of work and written documentation was agreed with Health and Safety Advisors.

During this process an emergency request was received from the client, at 01:30 one morning, to replace all removed access dowel sections as soon as possible as the normal flow of 20MLD was required to support distribution following a catastrophic failure of a strategic main in another part of the network.

Due to our approach and cleaning process, we were able to hand the entire 14.964km of main back in a sterile condition to allow charging within 12 hours.

“We found the Fastflow system to be very effective in terms of achieving long cleaning lengths, single pass operations and very good post cleaning water quality results.”

Stuart Tilley, Network Projects Manager, NWL.