Tests show successful elimination of infiltration

Tests by Thames Water have demonstrated the success of a new sewer lining technique developed by pipe manufacturer Epros of Germany. Independent consultant Paul Hayward reports on a sewer liner that is the first to reduce infiltration to zero.

German manufacturer Epros has introduced a new cured-in-place sewer lining system that eliminates the gap between the liner and the host pipe. Where a sewer liner is required, to eliminate infiltration as well as to restore structural integrity, it is essential to eliminate any paths through which infiltration could flow.

This is especially true if it is necessary to cut holes in the liner in order to reopen laterals. Unless the liner is genuinely a tight fit, leaving no annular space as a leakage path, infiltration can still enter the system.

To achieve this, the liner must not exhibit any appreciable shrinkage, either chemical or thermal, during cure. Many resins contain unreactive components that function as carriers or are intended to control viscosity, such as the styrene in polyester resins, and the evaporation of these during the curing process will almost inevitably lead to shrinkage.

Thermal shrinkage is a function of the difference between the ambient temperature and the temperature to which the liner rises as it is curing – through the circulation of hot water, the exothermic reaction of the resin components, or both. As the liner cools, again, it will shrink.

Until recently, most liner manufacturers and installers have insisted that shrinkage is minimal and that surplus resin will fill any gaps, so there would be little chance of any significant groundwater flow between the liner and the host pipe. Tests witnessed by Thames Water’s Don Ridgers, at Epros’ headquarters in Duisburg, have shown that this is not the case.

The tests were designed to assess the performance of the liner when subjected to an external head of groundwater. Conventional lining systems can allow substantial groundwater flows to enter the system through the annular space between the liner and the pipe.

The Epros Seal Liner is the first lining system to show zero leakage in Thames Water’s tests, which subjects the cured liner to 5m external head of water through simulated leaking joints and a lateral connection. Using a non-woven fabric and a specially formulated epoxy resin, the Seal Liner exhibits negligible shrinkage whilst providing high structural strength.

Epros’ managing director Michael Mühlin commented, “The extent of the shrinkage problem has not been fully appreciated by the renovation industry in the past, and we are pleased to be the first manufacturer to have tackled and solved the problem.”

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