Frequently asked questions​

For what kind of pipes is the F-lining system used?

The system is designed for use in laterals and small wastewater pipes. The field of application is sewer lines in properties, e.g. pipes connected from a building to a mainline or roof drainage and area drainage. Moreover the system can be used to line road drainages or drainpipes within industrial complexes. Both horizontal and vertical pipes can be renovated.

What functions does the system fulfill?

The old pipe is renovated. The system rebuilds both the static load bearing capacity and tightness of the damaged main system.

Is there any long-term experience with the system?

The technique has been used successfully for the past 9 years in Denmark and for several years also in Sweden and Norway. Currently between 50 and 100 kilometers (31 and 62 miles) of the F-liner are installed in these three countries per year. In Denmark the system has already successfully passed the warranty period of 5 years.

Is there any approval?

The F-liner has a German approval from DIBt (German Civil Engineering Institute). A QUIK approval is in preparation for Switzerland.

What useful life can be assumed?

Bluelight F-liner is a LED curing lining system that ensures a useful life of approx. 50 years. A standardized test has been running for 10,000 hours to measure creeping of mechanical properties. This test simulates the ageing process of the synthetic after 50 years. The determined parameters of the raw material are the basis for the static calculation of the F-liner.

What is the efficiency advantage of the Bluelight system over epoxy resin systems?

Given comparable material costs, a higher installation speed results in an efficiency advantage. Epoxy resin systems normally have length-independent heating periods of several hours. Depending on the installation length the curing time for the F-liner is from a few minutes up to 45 minutes at the maximum and is realized by a set of LEDs. The system is at least twice as fast as conventional heat-curing systems. However, the efficiency advantage can be three, four or five times higher depending on the job site properties.

Does the renovation process smell?

No. Styrene-free vinylester resin does not smell at all. The resin can be transported without labeling and is harmless. Because the system cures with LED light, there are no steam emissions at the site.

Do I always have to order impregnated liners or can the liners also be impregnated on site?

The client may choose between ordering the impregnated liners, impregnating the liners on site or impregnating them in its own stationary facility.

What is the shelf life of the impregnated liners? What must be kept in mind for storage?

To preclude an early reaction, the impregnated liners have to be stored in darkness and protected against light. The shelf life is highly dependent on the temperature during storage. By cooling the liners to a temperature of 10°C they can be stored up to 3 months without losing quality. At a temperature of 20°C the liner can be stored up to one month between impregnation and installation. At a temperature of 25°C the storage time is one week. At temperatures over 30°C the liner will be damaged after a few days. Storage of impregnated liners at temperatures over 25°C should be avoided.

What kind of damage occurs if the impregnated liner is stored too warm?

The PU coating of the impregnated and not yet cured F-liner absorbs the resin depending on the ambient temperature. This process increases with the ambient temperature. The absorption of the resin leads to a volume increase of the internal coating. As a result the internal coating becomes wavy if storage is too long and warm. The non-installed material will show visual issues then.

Is this effect also relevant for installed liners in a pipe?

No. As soon as the liner is cured in the pipe, the resin and the solvent polymerize to a permanent, cured plastic. Reactions of the PU coating and the cured laminate are then no longer possible.

What has to be kept in mind concerning impregnation at the job site?

The already mixed styrene-free vinylester is delivered in bundles. The client can also obtain the resin in an IBC tank. It should be impregnated at temperatures of 21°C ± 3°C. It is important to impregnate the liners in a climate-controlled, closed room without light in the blue wavelength range (approx. 450 nm). You should install a lightproof curtain on the doors or opening as well as a filter film on the window if necessary. Furthermore you should use special lamps for lighting the area where impregnation happens (e.g. Orizon 12 V 1022 mm LED interior light 48 LEDs in a Metolight ASR-G10-120-T8, gold, 520 nm, UV-filter tube, 1200 mm long). The amount of resin has to be weighed out exactly. Otherwise the liner can be overstretched already during the impregnation process by using too much resin per meter. Too little resin per meter will lead to soft patches without enough resin in the cured liner. Every client receives detailed instructions on impregnation. Impregnation has to be done in a vacuum and with an adjustable calibration roller.

Is there any health risk during the impregnation and installation process?

During impregnation and further processing of the F-liner direct contact between the resin and the skin should be avoided. For this purpose suitable protective gloves and eyewear should be used. Allergies, such as to epoxy resin, are not known in conjunction with the styrene-free vinylester resin used in the F-liner.

What is the best way to store F-liners?

A distinction must be drawn between decentralized (mobile) storage on the rehabilitation vehicle and centralized storage, e.g. at a depot. The impregnated liner has to be stored in a lightproof box at a temperature of 20°C on the rehabilitation vehicle. The box should be air-conditioned via a rechargeable battery pack so that the temperature can be maintained even if the vehicle is out of use at night or at the weekend. Centralized storage should be in lightproof surroundings and below 10°C to realize the maximum storage stability of 3 months.

How is the F-liner installed?

The F-liner is inverted with air pressure (pneumatically).

What kind of technique is necessary for inversion?

For inversion you can use conventional inversion drums. To integrate conventional pressure tanks and elbows with a Storz coupling, an adapter from Storz to Camlock is needed. This adapter can be ordered together with the components. Please note that the impregnated liners have to be protected against sunlight at all times. Hence lightproof pressure tanks have to be used. If inversion drums with a window are used, the window has to be laminated with a film that filters out the wavelength of blue light on the outside. In our opinion inversion drums are ideal for insertion because the process can be controlled slowly and continuously.

Is it also possible to work with a liner gun?

A liner gun is not recommended because the liner is generally exposed in the feeder to the gun. Therefore it is exposed to sunlight, and this is not advisable from our point of view.

What temperature is ideal for inversion?

For optimum rehabilitation results the F-liner should have a material temperature of 20°C ± 2°C during installation. A lower installation temperature leads to reduced flexibility of resin and PU coating during the inversion. Worse inversion behavior in tight elbows and increased winkles on the inside of the elbow can be the result.

How is the curing process of the F-liner performed?

The curing of the F-liner is realized by a set of LEDs operating in the wavelength of blue light (450 nm). This range is part of daylight. The LEDs produce exactly this wavelength. The resin has an admixture of a worldwide patented photo initiator that reacts specifically to this wavelength.

What pressure is used during inversion and installation of the liner?

The liner is inverted at pressures up to 1.5 bar and cured within a pressure range of 0.5 to 0.9 bar. If the pressure is too high, there is a risk that the head of the liner or of the silicone supporting hose will burst. The pressure that is necessary for the inversion process depends on the inversion equipment used (drums, hoses, elbows). Detailed instructions are found in the guidelines.

Is it possible to install with an open end?

Yes. The system can be installed from manhole to manhole as well as from a single manhole. The liner can be inverted with a closed end. In this case the head will be milled off. Installation with an open end is also possible if a translucent and reinforced silicone inner hose is used.

Is installation without a preliner possible?

In general, installation without a preliner is technically possible. This is restricted to cases where the pipe to be relined is free from infiltrating ground water, free from water-carrying side connections and without severe damage that can cause an uncontrolled leakage of resin. Generally the use of a preliner improves the quality.

Is installation in pressing groundwater possible?

Yes. Basically installation against pressing groundwater is possible. In this case it is mandatory to use a preliner. Furthermore it is also mandatory to use a side entrance for the installation so that the overall system is kept under overpressure from inversion until it is permanently cured. Non-temporary stoppable side connections with strong water ingress on the line that needs to be renovated should be classified as pressing groundwater.

What nominal diameters are possible?

The system has an approval from DIBt (German Civil Engineering Institute) within a diameter range between 100 mm and 300 mm (4 inches to 12 inches). The system is most efficient in a diameter range between 100 mm and 200 mm (4 inches to 8 inches), which reflects the classical range of laterals. Consequently diameter ranges of more than 200 mm (8 inches) make sense in exceptional cases if some short pieces with a diameter of 250 mm (10 inches) have to be renovated as a part of an entire order that includes pipes with a diameter range between 100 mm and 200 m (4 inches to 8 inches). However the system isn’t designed for renovations of more than 250 mm (10 inches). In this case classical UP-resin systems are more efficient.

Does the F-liner stick to the old pipe?

The F-Liner doesn’t stick to the old pipe. It relines the old pipe with a close fit. Installation of the preliner prevents bonding. If installation is done without a preliner, adhesive effects could be the result. Some market players allege that overall adhesion can occur. According to our knowledge and experience this is highly unlikely in practice, also when using epoxy systems, because a strong sticking effect between the liner and the old pipe could only be achieved if the old pipe were completely free from all release agents and milled all over before inversion happens. However, these conditions cannot be created in an efficient manner and normally you can’t find them in reality.

Do various F-liners stick together?

If an F-liner with an open end is inverted into a side connection that is connected to a mainline already relined with an F-liner, the liners will stick together due to excess resin on the last inserted F-liner. However, this requires a clean connection compartment.

How long does an installation take?

The system has a curing speed between 0.3 and 1.33 m/min (1.0 and 4.4 ft./min). For further details see In addition to the nominal diameter and the light source used, the curing process also depends on the length of the installation section. Usual lengths of laterals are normally cured in less than half an hour. Added to this is the extra time needed for preparation and follow-up as well as for impregnation on site (if no pre-impregnated liners are used), cutting off and winding the liner into the inversion drum, inversion of preliner if needed, inversion of the F-liner, inversion of the supporting hose if needed (in case of installation with an open end) and manual cutting of liner ends at the manhole or with the robot inside the pipe. Normally the whole installation including preparation and follow-up takes only about one hour.

What kinds of bends are possible?

A distinction must be drawn between the capability of the liner to coat bends as fold-free as possible and the need to push the LED head to the end of the liner inversion manually. 

  1. Capability of the liner to coat bends as fold-free as possible: Bends up to 30 degrees: fold-free on the inside of the bend, bends with 45 degrees: minor folds could be formed on the inside of the bend, bends with 90 degrees: folds will be formed on the inside of the bend. Examples of results in practice:
  2. Pushing in the LED head: Bends up to 90 degrees are possible with the small LED ball head in a diameter range of 100 mm (4 inches). The limiting factor for successful pushing in of the small LED ball head could be a line including multiple bends. Multiple bends can cause high friction, which will resist pushing. In case of uncertainty at the site one should try to push the LED head after installation of the preliner and before inversion of the F-liner.
What lengths are possible?

The maximum installation lengths are dependent upon the length of the supply cable of the curing unit. The small curing unit has a supply-cable length of approx. 40 m (131 ft.), the big curing unit of approx. 50 m (164 ft.). The distance between curing unit and starting point of the pipe reduces the maximum curing range. If two manholes exist it’s basically possible to work with two curing units from two sides, in this way renovating twice the supply length. In this case the system has to be kept under pressure continuously. Installations with open end using silicon supporting hoses are limited to a maximum of 25 m (82 ft.) because otherwise the removal of the supporting hose could become a risk. If installation with an open end is necessary over longer distances, installation with a closed end and subsequent opening of the closed end by a milling robot should be preferred.

Can the F-liner expand to a bigger diameter?

If the F-liner is installed with a closed end (without supporting hose) a radial expansion of up to 133% of the nominal diameter is possible. In this way one nominal diameter change within a line can be performed by one and the same F-liner. A liner with a nominal diameter of 100 mm (4 inches) can be extended to 125 mm (5 inches), a liner with a nominal diameter of 125 mm to 150 mm (5 inches to 6 inches), a liner with a nominal diameter of 150 mm to 200 mm (6 inches to 8 inches) and a liner with a nominal diameter of 200 to 250 mm (8 inches to 10 inches). It has to be taken into account that the wall thickness decreases proportionally with expansion. If a liner with a nominal diameter of 150 mm (6 inches) with a wall thickness of 4.5 mm (0.2 inches) is expanded to DN200 (8 inches) it will have a reduced wall thickness of approx. 150/200 x 4.5 mm=3.4 mm. During installation with an open end using a silicon reinforcement hose the F-liner can achieve a radial expansion up to 125% of its nominal diameter. A nominal diameter change isn’t possible in all diameter ranges using one and the same liner. A liner with a nominal diameter of 100 mm (4 inches) can be extended to 125 mm (5 inches), a liner with a nominal diameter of 125 mm to 150 mm (5 inches to 6 inches), a liner with a nominal diameter of 200 mm to 250 mm (8 inches to 10 inches). A nominal diameter change from 150 mm to 200 mm (6 inches to 8 inches) using inner hoses is risky because an overstretching of 133% would be necessary. If the expansion is performed using an open end installation and a silicon supporting hose, the bigger nominal diameter for the silicone hose should be chosen. For example, expansion from 125 mm to 150 mm (5 inches to 6 inches) means use of a 150-mm (6-inch) silicone supporting hose.

Can the F-liner totally replace our epoxy-resin systems?

No. There will be some special tasks left that cannot be performed by the F-liner at this stage. An example is when there is more than one nominal diameter change in the same pipe or several very tight turns in a line, so that the light sources cannot be pushed in. For those occasional tasks epoxy-resin systems should still be available. Therefore we advise integration of the Bluelight technique into an existing 2-component system.

Is it possible to use compressors and power supplies that already exist?

Yes. However the compressor should have a minimum output of 1400 l/min (50 cfm) at 7 bar as well as a downstream cooling and drying because the compressed air is used for cooling the LED head. Without drying the air harmful effects could occur. Cooling and drying can be upgraded by most standard compressors. For a proper inversion of longer installations higher outputs than 1400 l/min (50 cfm) at 7 bars are necessary.

Is it possible to use the camera that is integrated into the LED heads for CCTV?

No. The integrated camera isn’t intended for this purpose. The camera that is integrated into the LED heads serves as a control camera only. It helps to locate and push the LED head towards the end of the liner and makes it possible to control the liner before curing. For a CCTV inspection separate systems are recommended.

What servicing is needed?

The LED heads should be cleaned regularly. Clients are supplied with a cleaning set and instructions on how to use it.

Is it possible to do maintenance work by myself?

No. The LED heads have to be checked after 50 working hours for the first time. Afterwards the check should be repeated every 150 working hours. This work has to be performed by a competent dealer that can check the light intensity. The current working hours are shown on the curing unit.

What happens if total light intensity becomes insufficient because single diodes break down?

The LEDs will be replaced as part of servicing by a competent dealer.

What is the service life of the LEDs?

With regular cleaning of the LED heads replacement of the LEDs is not to be expected before 200 working hours.

What support do I receive if I buy the system?

Buyers of the system will be trained intensively by Bluelight technicians. The individual amount of training has to be determined depending on the client’s needs.

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