How to stop lining shrinkage

Over the past 30 years, Insituform Technologies has built a reputation for installing cured-in-place pipe-lining systems that are inverted using water. But it has also developed a variety of other innovative pipeline rehabilitation systems.

Normal systems have the potential that, once cured, the liner may develop an annulus between the host pipe wall and the outer skin of the lining material. While this slight shrinkage of the liner is not normally an issue in most sewer rehabilitation works, there are circumstances in which it might be desirable that the resulting annulus is eliminated from the rehabilitated pipe.

A sewer with a high infiltration rate due to external ground water pressures is one such case. Another is where lateral connections cause the mainline to be opened beneath the water table to take the connection.

Many systems have tried to overcome this potential problem in a variety ways. But now Insituform Technologies has launched a new lining product that guarantees a tight fit, no annulus lining process.

The Leak Tight liner system uses an established epoxy resin system as the basis of the lining process. The resin used effectively reduces liner shrinkage to nil during the curing process, when used with Insituform's standard non-woven fabric liner tube.

Depending on the circumstance of the lining operation, the liner tubes, the curing process used and the final product requirements are available with either polypropylene, polyurethane or polyethylene inner coatings.

Infiltration testing
Last August, Insituform undertook infiltration testing of the liner to fully establish claims of the product and the effectiveness of its installation. Testing of the lining was witnessed by WRc as part of an ongoing, 18-month-long test programme for Thames Water, which has been looking at various lining systems and their infiltration characteristics post lining and curing.

Using a test rig, designed by Don Ridgers at Thames Water, sample linings are installed and cured while a 3m head of water pressure is applied to the test rig using simulated leaking defective joints and a lateral connection. Once the liner is cured in the pipeline, this test pressure is increased to a 5m head of water.

Any leakage between the host pipe and the liner is then measured.

On the tests, two lining runs were completed. The first comprised the installation of a test liner using water inversion and hot water cure techniques. And the second used compressed-air inversion and steam curing - a technique recently added to the Insituform liner installation portfolio.

The test results showed that, in both cases, the liner could be installed with no leakage between the host pipe and the liner. There was no percolation of infiltration water along the liner / host pipe interface bond, proving the cured liner produced the close fit lining claimed by Insituform's new Leak Tight liner product.

The new Leak Tight lining product is currently available in a range of diameters from 100mm upwards. It can be installed over lengths of up to 200m.

Further advantages for the Leak Tight lining system are that it is odour free during installation and does not produce styrene or other volatile solvents on application. A further advantage of the steam cure option is that linings up to 375mm diameter can be installed and cured in as little as three hours under the right conditions.

For WRc, Kevin Adams says: "The infiltration test has been designed as an arduous examination of a lining system by the wastewater industry itself. And it has been independently witnessed by WRc.

"The test in some instances has proved that water will track between the host pipe and lining where there is a path left by the lining installation process, thereby only moving the point of infiltration rather than stopping it.

"The test is a quantitative assessment of a lining's ability to stop or reduce infiltration to the levels currently required by the water industry. The success of a lining system in this test will therefore give contractors proof of the performance being asked for by the asset owners. Insituform's Leak Tight tests, for both the hot water and stream cure versions, showed no measurable infiltration from between the lining and the host pipe, showing that the lining had successfully bonded to the host pipe."

WRc witnessed the installation and infiltration testing and has issued a letter to Insituform detailing the system materials and processes and confirming the success of both curing methods for the lining.

Commenting on the success of the new lining system for Insituform, business development manager John Beech says: "Thames Water has utilised and refined the test procedure used on our Leak Tight liners for some 18 months now, so we know that it is very rigorous.

"In reality, most sewer pipelines do not operate in ground water of 5m static pressure head, so a test such as this really does show how effective our liners are once installed.

"We are also delighted that our association with our new resin supplier now allows us to offer an even greater range of lining products, with application to a much broader range of challenging ground conditions, to our existing and potential customer base."

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