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Pitching for patching

Advances in preventative maintenance and localised sewer renovation technology are being boosted by increased client spending levels, reports Mike Walter.

The level of investment allocated by privatised water companies to the high-tech maintenance of their wastewater infrastructure has been increasing in recent years. Periodic monitoring of sewer lines and preventative maintenance is becoming the norm, with a growing number of specialists able to provide a comprehensive service using automated technology.

The frequency of renovations to defective sewers means use of the latest trenchless techniques is on the up.

Seven water companies in England and Wales surveyed by NCE confirm growing levels of investment. Severn Trent Water says that since privatisation of the water industry in 1989, it has spent 631M specifically on sewer maintenance and renovation. In 1992 alone it spent 108M, the allocation falling to 45M but rising to an annual spend of 68M since.

At South West Water, spokesman Paul Breakwell says: 'Approximately 40% of our revenue expenditure is proactive, aimed at the assessment of sewer condition and the prevention of faults. A planned, preventative maintenance system is used to prioritise and track activities on key elements in the sewerage system.'

Keeping pace with the rapidly developing equipment and techniques is especially important for contractors involved in term maintenance contracts with water companies for the ongoing provision of services.

Premier Pipe Services' sales and marketing manager Bryan Lord says: 'Some water companies are setting themselves vigorous targets in the amount of maintenance carried out on their sewers. As workload increases, so does the competition and increasing numbers of specialists are becoming highly efficient and very competent at lining.'

Effective maintenance largely depends on a programme of early monitoring to prevent a fault becoming a failure. Studying images relayed from closed circuit television cameras is nothing new, but a technique that was once relatively unusual is now commonplace.

Protruding sections of adjoining pipework, leaking joints and deformed sewers are three faults which can easily and accurately be located by a robotic eye sent down a wastewater conduit. An engineer at ground level can remotely control a mobile camera - launched from a manhole shaft - either to locate a suspected defect or identify a new area in need of attention.

Perhaps the most effective trenchless technique to have evolved in recent years is pipe lining. Traditionally, small areas of leaking sewer have been repaired using an inner lining placed in one complete section between two manhole shafts. The successor to this all-embracing renovation is patch repairing which is becoming increasingly popular. Localised problems can be repaired at a reduced cost by a smaller operation which required a fraction of the lining previously used. 'Most sewers only suffer from 2m to 3m of defect in a 100m length. Manhole to manhole lining requires material to line a lot of pipe, which is an uneconomic means of solving what can be a localised problem,' says Rae.

Full length linings do still play a crucial part in renovation, especially in the structural rerounding of 100mm-600mm diameter pipes which have lost their desired shape by up to 35%. A hydraulically expanding re-rounding device is winched into place from a manhole shaft and is used to force a stainless steel shield to the circumference.

After 'roundness' has been achieved and the device has been removed, a full length polyester felt lining is placed by filling it with heated water which then cures the material hard up against the existing sewer.

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