Trenchless International spoke with a range of companies regarding the different curing methods used on the CIPP lining systems.

Heat curing techniques for lining and repair

Trelleborg Epros, through its epros product range, recently launched a new range of epoxy resins for CIPP liner applications. The company also has a range of silicate resins for use in the pipe lining rehabilitation field. In terms of the techniques which can be applied using these resins they include ambient cure, hot water cure and steam cure of CIPP liners. The resins can also be applied to localised repair patches, lateral liners and lateral connection seals.

The company’s resins are available for use with not only its own lining products such as the epros DrainLiner, epro DrainPlusLiner and epros SealLiner, but also with other proprietary liner materials.

In a perfect world CIPP liner resins would have a long pot life and a short cure time. Whilst chemistry does not normally work like that and generally a longer pot life equates to a longer cured time, the latest epros resin developments now offer longer pot life with short cure time, especially where steam cure techniques are used.

Cure options

Ambient curing relies on, as the name indicates, the ambient temperature of the liner location to cure the resin impregnated liner. epros ambient cured silicate resins offer a pot life of 10 to 30 minutes with cure times of between 30 minutes to 2 hours. This makes them ideal for installations such as patch repairs, lateral connection seals or for short lining lengths of around 30 metres of typically 150 mm diameter liner.

The longer cure times for ambient operations established the need for the application of heat to accelerate curing of the resins. This requirement led to the development of two widely used techniques of heat based CIPP liner curing – hot water cure and steam cure.

Hot water curing requires the use of a boiler and water circulation pump system to bring the water to the required temperature throughout the liner installation. Mini (90 kW) boilers are more often used where laterals and short lengths of mainline are being rehabilitated. For example, the heating of a liner during cure allows a contractor to cure in two hours an epoxy impregnated liner that would normally take four hours to cure in ambient conditions.

Normally, hot water cure is undertaken at temperatures of between 65 and 90 degrees Celsius using epoxy resins. Trelleborg said epoxy resin takes less energy to cure and are designed to give higher strength and low shrinkage, particularly when steam cured. The e-modulus for epoxy resins can also be two to three times higher than the minimum specification requirement for the long term operation of a liner post installation.

Examples of epoxy curing show that the resins can cure at lower temperatures, for example 65 degrees Celsius, and this will give a two and a half hours cure. At 80 degrees Celsius this cure time is reduced to one and a half hours. With steam the cure time can be reduce to as little as 30 minutes.

The development of the steam curing technique for smaller diameter applications has come with the development of mini steam generators. These portable units offer quick installations times and normally operate with a compressor. The steam used is normally superheated at 120 degrees Celsius, allowing the resin to cure quickly whilst reducing condensation within the liner.

For larger diameter installations bigger steam generators are required. In these cases curing can accelerate cure times from between six and seven hours using normal hot water boiler techniques to just three to four hours with steam.

The latest developments in the epros epoxy product range now offer a pot life of 40 hours and, with steam curing, a cure time of just three hours, bringing product availability much closer to the ‘ideal’ sought by the industry.

Liner developments in both materials and coatings, have also been made to ensure that the liners and resins can withstand the rigours of steam curing. The latest testing of the epros liner product range with WRc shows the company’s designs can offer an expected design life of 50 years plus.

Insituform Technologies has a dedicated team of experienced engineers who develop new products and processes in order to better meet customer needs. The process includes field/pilot installations for new products. Insituform has 64 US patents and 20 pending US non-provisional patent applications relating to the Insituform CIPP process. In addition, the company has 25 issued foreign patents and 153 applications pending in foreign jurisdictions. Insituform remains dedicated to research and development efforts and recently launched the InsituMain process, a fully-structural CIPP solution suitable for pressure pipes.

Insituform cure with either hot water or steam. The company said that curing CIPP with steam can reduce energy usage during installation by approximately 95 per cent.

Research conducted by the Trenchless Technology Centre at Louisiana Tech University to establish the long term structural behaviour of CIPP demonstrated that the Insituform product design life exceeds 50 years.

Wet out

Insituform’s patented serial vacuum impregnation process ensures the resin fully saturates CIPP tubes of any length or thickness. The company said that it is important for long term reliability that the patented method is used during wet out to ensure the resin completely fills the CIPP tube. Creating a vacuum in front of the resin, the method draws the rein along the tube. The suction lines are moved along the tube as the resin moves. Insituform said vacuum impregnation also ensures that the tube contains resin, not air, for uniform strength, enables wet out at any length, diameter, or thickness, and allows a faster wet out in less space, saving on time and cost.

Let there be light

Brandenburger is a leading company in light curing GFRP pipelining, with more than two million metres installed in 28 countries. The technology works with circle profiles in diameters of 150-1,000 mm and egg-shaped profiles 200/300 – 800/1,200 in rehabilitation lengths of up to 300 metres.

Resins

There are two light curing resins. The unsaturated polyester resin is used for the rehabilitation of rain, waste and combined sewers with good durability against acids and leaches. Vinylester resin is used in industrial sewers with high durability against acids and leaches even in combination with higher water temperatures.

Lighting up CIPP liners

A lamp train with UV modules is pulled through the form-fit calibrated liner with pre-calculated speed. The special characteristics that differentiate the Brandenburger liner are:

* Use of seamlessly wound liners out of glass fibre laminate webs; * Unique saturation of the raw materials before the production of the pipe liner with UV-reactive UP resin (possibly with addition of peroxides for the variation ‘hybrid curing’ for larger wall thicknesses over 10 mm); * Drawing in the liner on a protective foil and form-fitting expansion using compressed air; and * Curing of the liner using precisely dosed UV exposure – ‘BLUETEC® technology’.

To read a Brandenburger project article please click here.

Per Aarsleff A/S use UV light, steam, water curing techniques. For a number of years the company has also been developing a unique curing system for the curing of felt liners by means of LED light.

The unique feature of this new method is that it combines the use of light-emitting diode (LED) light with a label-free resin system in a combination with both felt and glass liners.

The method has been developed in cooperation with Per Aarsleff’s resin supplier DSM, and the method is designed to allow the use of other types of resin systems. The design work has produced a number of auxiliary tools including a LED light train patent applied for this type of application.

When comparing LED curing with steam curing, the advantages include:

* Significantly reduced energy consumption. * Reduced curing time concerning installation of short stretches. * Reduced number of disturbances to the intermediate environment at the installation site, as no steam is emitted into the environment. This especially proves advantageous to installations situated close to or inside buildings.

When comparing LED curing with conventional UV curing, the advantages include:

* Long-lasting durability of lights (LED has a durability of up to 50,000 hours). * Reduced energy consumption. * Curing of felt liners (due to the special formula combined with LED light). * Curing of liner systems with permanent inner coating. * Curing of thick glass liners. * Reduced heat generation from tools applied, allowing the system to be used for small dimensions as well. * Curing of styrene-free applications. * Fast curing.

At the moment, Per Aarsleff A/S has three work units applying LED curing and has executed more than 600 installations. For a project profile using the technology please click here.

Aqua-Pipe – the potable water pipe solution

Sanexen developed Aqua-Pipe approximately nine years ago in collaboration with the NRC to rehabilitate drinking water mains. Aqua-Pipe is designed and installed according to ASTM F 1216 and ASTM F 1743 standards respectively and is designated as a class IV fully structural lining when compared to the AWWA M28 structural classification.

This means that Aqua-Pipe is a standalone structural liner that can withstand all dead and live loads and internal pressures including vacuum without the help of the residual strength of the existing pipe. If the host pipe is depressurised, Aqua-Pipe will resist the external dead and live loads and can withstand operating pressures up to 150 psi.

The proprietary epoxy resin used has no effect on water quality and contains no VOCs. There is no styrene in the epoxy resin. The liner is pulled in place and cured by circulating hot water.

Aqua-Pipe is made of two circular woven (seamless) polyester jackets with a watertight polymeric membrane fused to the inner jacket. One of the advantages of rehabilitating a water main with the Aqua-Pipe process is the resulting increase in the Hazen’s Williams coefficient (C factor > 120).

In general, all types of water mains from 6 to 12 inch diameter can be structurally rehabilitated with the Aqua-Pipe technology. Cast iron and ductile iron water mains are the most common pipe materials which have been rehabilitated to date, but other material types such as asbestos cement, steel, PVC, concrete or others can also be rehabilitated if required.

The key success to the process is that all services are reinstated from within the lined pipe with specialised robotic equipment developed over the years, therefore there is no need to excavate in front of every house to open service connections.

Using a safety factor of two, the service life of the Aqua-Pipe product is 50 years. This means that the product will retain 50 per cent of its initial flexural modulus properties after 50 years all things being equal otherwise.

Over 900,000 feet of liner has been installed through North America with the help of licensees. To comply with North American drinking water regulation, Aqua-Pipe is certified by NSF to NSF/ANSI standard 61.

Enjoying the ambient cure

Perma-Liner Industries, Inc. is devoted to being on the forefront of lining technology and constantly evolving to meet the diverse needs of installers. The company has all of their materials certified third-party tested and approved lining materials. Perma-Liner Industries has a 30,000 square foot facility with a dedicated area and staff to developing new products as well as improving on our existing products.

The resin is 100 per cent solids epoxy with no shrinkage to allow annular space between the host pipe and new liner. This eliminates the chance of roots or infiltration into the sewer system. The epoxy resin supplied by Perma-Liner is environmentally safe with no styrene additives. This formulated Epoxy resin has a cure time of three hours consistently without using external heat sources. The resin is also manufactured in the USA and meets EPA/DEP regulations. When demonstrated in exposed pipe samples, the epoxy resin bonded tightly against the existing host pipe sealing off open holes and cracks.

The liner and resin supplied by Perma-Liner Industries has been tested to meet the strength requirements of ASTM F-1216-07b CIPP installation and physical property requirements. ASTM F1216 specifications require a minimum life expectancy of 50 years, which the products exceed. The Perma-Liner resins are formulated for different ambient working temperatures to ensure a three hour cure time, with a consistent 45 minute working. To view a project article please click here.

Contributors to this feature include Per Aarsleff’s Peter Lystbæk, Aqua-Pipe, Brandenburger, Insituform, Trelleborg Epros, Perma-Liner Industries Inc.