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Retint for Dartmouth water colours

UTILITY NETWORK service company Subterra has carried out rehabilitation works on a 26km section of water main from Venford Water Treatment Works on Dartmoor to Paignton in Devon.

South West Water commissioned the £1.7M project because the original 230mm diameter gravity fed cast iron pipe had corroded and was discolouring the water. It was still structurally sound and was taking pressures up to 23.8bar.

Subterra chose a Subcoil lining system for the project. Wavin Plastics supplied the Subcoil pipe as factory-folded and strapped polyethylene pipe on coils.

Work was due to start early in February 2001 but was delayed until March by the outbreak of foot and mouth disease.

When work did get under way, the thinwalled polyethylene pipe lining was installed with restraints around it to keep it in a U shape, reducing its effective cross-sectional area. Once the main was cleaned and scraped, the Subcoil liner was winched directly into place through the host pipe which is buried at up to 3m depth.

Once in place, the new liner was pressurised, breaking the temporary restraints. The pipe then continued to expand to form a close fit within the host pipeline. The ends were then trimmed and sealed to the ends of the host pipe, allowing it to be returned to service. The 5.4mm thick lining sealed the leaking joints, even with the high pressure environment.

Subterra said an open cut solution for the pipeline would have been more expensive and caused greater disruption to the small roads on the already difficult terrain of Dartmoor.

Two teams installed the Subcoil in lengths of up to 460m at rates of up to 1,400m a week per team.

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