Withstanding the pressure: liners for pressure sewers put to the test

Pressure sewer pipes like gravity sewers that are getting on in years need to be renovated. But, which methods are suitable? What are their strengths and weaknesses? The recent IKT comparative product test on pressure sewer liners provides answers.

Experimental setup of pressure sewer pipes in the IKT large 1:1 scale test facility

Pressure sewers are critical and sensitive elements of urban wastewater infrastructure. Many are ageing so sewer network owners are increasingly having to deal with their rehabilitation and there are different methods available on the market for this.

Consequently, the neutral, independent and not for profit IKT Institute for Underground Infrastructure, in Germany, has been examining rehabilitation solutions in an extensive comparative product testOver a three-year period an evaluation project was undertaken on behalf of six municipal network operators from Bottrop, Bremen, Burscheid, Iserlohn, Cologne and Voerde and two regional water associations, the Emschergenossenschaft and the Wupperverband.

The project was supported by the district government of Münster and the State Office for Nature, Environment and Consumer Protection of North Rhine-Westphalia (LANUV). It was financed jointly by the NRW Ministry of the Environment and the eight network operators.

These organisations formed a steering group that determined the pressure sewer damage scenarios to be remedied, the testing programme and the evaluation of the results. IKT developed the test concept, set up the test rigs in its large 1:1 scale test pit and carried out the testing.

Six liners in the comparative product test

View of the built-in sewer pressure pipelines in the IKT large 1:1 scale test facility

The steering committee selected the following lining technologies for the comparative product test:

Close-fit linier method:

  • Compact Pipe (Wavin GmbH)
  • egeLiner (egeplast international GmbH)

Cured in Place Pipe (CIPP) liner process:

  • Esders HPS Liner (Esders Pipeline Service GmbH)
  • Nordiflow WPE (NordiTube Technologies SE)
  • SaniPipe (AMEX Sanivar AG)
  • Starliner Structure-S (Karl Weiss Technologies GmbH)

Remediation task

Schematic representation of the test setup in the IKT large 1:1 scale test facility

For each liner system, the test setup consisted of a DN200 steel pipe with damage patterns such as holes, leaky connections, point loads, transverse and longitudinal cracks, ovalisation and incrustations. This realistically depicted the damage that network operators find in their pipes.

Class A liner systems

The central issue was whether the liners are suitable as Class A products. A Class A liner must be able to withstand internal and external stresses on its own, regardless of the condition of the host pipe. The stress testing programme conducted as part of the IKT comparative product test went well beyond the regular warranty period of five years in order to consider the entire useful life.

Test program and evaluation scheme

Simulation of external water pressure: After flooding, part of the test setup is reflected in the water

The test programme consists of three phases: The first phase depicted the regular, normal operation of a rehabilitated pressure pipe. Internal water pressures of between 2 and 6 bar were applied at different flow speeds.

In the second phase, the degeneration of the host pipe was simulated over a prolonged period of time. For this purpose, some of the damage scenarios in the host old pipe were worsened in order to simulate progressive damage development and the resulting changes in external influences on the liner. Test pressures and flow rates remained the same as in the first phase.

Finally, the third phase served to simulate additional, non-every day and extraordinary loads on the liner that may occur over the course of its useful life. These included high-pressure cleaning at 80 bar, abrasive substances, the rapid switching on and off of the pump or elevated groundwater levels, such as those that occur when pipes pass under rivers.

Examination of the renovation results in the IKT large 1:1 scale test facility

Evaluation criteria

The overall grades for the liner systems are made up of the four main criteria of tightness, stability, operational safety and quality assurance. These are divided into nine sub-criteria. The range of grades lies between VERY GOOD (1.0) and INADEQUATE (6.0).

Watertightness criterion (weighting 45%)

The main weak points found in the four CIPP liner processes were the end connections to the host pipe, there were leaks. In contrast, the PE flange and electrofusion sleeve connections of the close-fit liners were reliably watertight.

The close-fit systems Compact Pipe and egeLiner proved to be watertight after renovation. In contrast, the picture for the CIPP liner end connections was very different: Nordiflow and SaniPipe each had to be reworked once to make them all watertight, whilst the Starline end connections had to be reworked twice in order to get them tight. The Esders HPS liner remained leaky even after the connections had been repaired twice and thus it failed on this criterion.

Stability criterion (weighting 25%)

Optical inspection of rehabilitated sewage pressure lines in the IKT large 1:1 scale test facility

The stability (load-bearing capacity of the structure) was classified by the steering committee as a central “KO” (failure) criterion. It was gratifying that five of the six liner systems tested passed this criterion with GOOD or SATISFACTORY grades. They show no or only minor abnormalities such as local wrinkling.

The SaniPipe liner failed this criterion as it collapsed under external pressure. The reason for this was insufficient fabrication of the liner, which took place without static proof. It was therefore not a Class A liner and consequently received the overall rating INADEQUATE, regardless of performance against all other criteria.

Operational performance criterion (weighting 15%)

This examined to what extent the liners can withstand normal operating conditions such as pressure fluctuations, abrasion, static pressures and high-pressure cleaning.

Clearly recognisable longitudinal fold in an installed liner

Here, Compact Pipe and egeLiner scored a GOOD grade. Also, they did not form folds and obstacles along their length. However, their installation leads to a hydraulic loss of 6% compared to unlined pipe this was in the middle range. The Nordiflow and Starline liners both had folds larger than 6 mm in the installed liners sheets and thus achieved a SATISFACTORY score. However, the hydraulic power loss of the Nordiflow was particularly high at 8%, whilst the Starline was the lowest at 3%.

With high-pressure cleaning, the Compact Pipe and egeLiner close-fit products achieved a VERY GOOD rating. Nordiflow and Starline withstood this operational stress SATISFACTORILY. On the other hand, Esders and SaniPipe failed this criterion because holes and delaminations occurred. Chemical loads did not have a negative effect on any liner system.

Quality assurance criterion (weighting 15%)

Although all the manufacturers provided an installation procedure manual, some of them have significant deficits in training, test certificates and external and internal monitoring. In addition, the installed Esders and SaniPipe liners each had a continuous longitudinal fold along the length and SaniPipe had design defects, which led to a devaluation of the grade.

Overall result and conclusion

The IKT comparative product test “Renovation process for sewage pressure pipes – Class A liner” confirmed that it is possible to achieve good renovation results. However, there are major differences in the performance of the six rehabilitation technologies examined, which are reflected in the test results awarded. One of the six liners could not qualify as a Class A liner.

Table of results IKT comparative product test “Renovation of sewage pressure pipes”


  • Compact Pipe (Wavin) GOOD (1.8)
  • egeLiner (egeplast international) GOOD (1.8)
  • Nordiflow W PE (NordiTube Technologies) SATISFACTORY (2.6)
  • Starline Structure-S (Karl Weiss Technologies) SATISFACTORY (2.6)


  • Esders HPS Liner (Esders Pipeline Service) DEFICIENT (5.3)
  • SaniPipe (Amex Sanivar) INADEQUATE (6.0)

Results at a glance and complete report (English)

The further deterioration of the condition of the host pipe over time was found to have no effect on the success of the rehabilitation. This applied in particular to signs of corrosion such as simulated pitting and point loads. Only in one case did the complete loss of the supporting host pipe lead to liner failure under external water pressure.

30° bend in a pressure sewer pipeline

All six of the liner systems could be installed through the four 15° bends included in the rig. Three of the liners were even able to install through a further 30° bend.

The systems were able to withstand normal operating conditions such as pressure fluctuations, abrasion and static pressure without any problems. However, there are clear limits to high-pressure cleaning and holes and delamination can occur here. Chemical stresses did not affect the tightness of the liner.

All liner systems lead to hydraulic performance losses in the pressure sewer the highest up to 8% at the top. The internal diameter was reduced by more than 20% in some places in some liners. Wrinkles >6 mm could be seen on all the CIPP liners. In contrast, the close-fit liners showed no creasing whatsoever, but there was clear ovalisation in the bends.

Liquid > Solid > Ready? Comparison of Five Flowable Backfills for Sewer Pipe Trenches

flowable backfill in test stand

Which flowable backfill best meets the requirements of sewer network owners? IKT has compared five candidates.

We have evaluated with sewer network owners the suitability of “Flowable Backfill” for use sewer trench backfilling in an IKT-Compare evaluation of this technology. Five products were compared and all were found to flow well into 1:1 scale excavation pits in our large-scale test facility – around pipes and manholes shafts and into every corner of the simulated trenches. However, during the subsequent performance tests it became increasingly clear that only three suppliers had actually installed “Flowable Backfill”. One product more or less concreted over the test pit, another material took far too long to set and posed a risk to working safety. The results have now been made publicly available.

IKT-Compare evaluation of Flowable Backfill in Sewer Construction
Results table in English (PDF)
Product test report in German (PDF)

Flowable backfill is also known as „Controlled Low-Strength Material“ (CLSM) or „Temporarily Flowable, Self-compacting Backfill Material“ (TFSB, or ZFSV in Germany). These products can be used to fill a pipe trench quickly, without the need for compaction equipment. They have the potential to flow into every corner of the trench, to bed the pipes optimally and to then harden to such an extent that you can build a pavement or road on top. And, if you need to access the pipe again later, the material can be dug out again – in the ideal case.

Advantages and risks of using Flowable Backfill

concrete manhole in test stand filled with flowable backfill

Flowable Backfill is useful, but the performace of different products is variable. Who has the best one?

The demands on the material are high. What if the supplier does not quite meet the optimum performance? What if after some time the road surface sinks, or in 20 years’ time you can no longer get to the pipe because the once-liquid soil is as hard as concrete?

It is not surprising that Flowable Backfills are popular. But, the enthusiasm of clients for their benefits often obscures awareness of the risks. IKT, as a neutral and independent institute, has considered these, working with with eleven committed wastewater network operators, to undertake a major comparative product test of the technology. So, in future wastewater network operators will know what to look out for when they order a Flowable Backfill.

Can a product deliver all the desired properties?

Five systems from five suppliers were tested under realistic, reproducible conditions in a large-scale test facility. After long and intensive preparation, the product test team spent a year testing, measuring, observing, evaluating and reporting. Now the results of this new IKT-Compare product test “Flowable Backfill in Sewer Construction”, funded by the NRW Environment Ministry, are available. The testing has basically confirmed the performance advantages of Flowable Backfill that network operators appreciate, but only if the formula and installation is correct.

It was found that all five materials were able to fill the trenches completely without voids – even when shoring removal was simulated after backfilling. The testers rated the pipe bedding provided by the products very positively, and a contribution to protection of pipes from tree roots can be expected from all the products. However, two Flowable Backfills failed to meet all criteria set by the steering committee (made up of wastewater network owners), as being essential for their use in sewer construction. One material hardened to such an extent that the required re-excavation capability was not achieved, another took far too long to achieve the strength required for building over, and also exhibited risks for re-excavating of the material and an unacceptable ammonia load during excavation.

Five participants at the start

flowable backfill flowing in test stand with concrete manhole

Everything in flux: When the flowable backfills were poured in, all was in order.

The five systems tested achieved grades varying from GOOD (1.9) to INADEQUATE (6.0) (on a scale from 1 to 6) – see link to results table below. In terms of quality, there are significant differences between the individual materials:

  • Carbofill from Thomas Zement GmbH & Co KG – GOOD (score 1.9)
  • RSS Flüssigboden from FiFB Research Institute for Flowable Backfill GmbH – GOOD (score 1.9)
  • TerraFlow from Heidelberger Beton GmbH – SATISFACTORY (score 3.4)
  • Terrapact by Holcim Beton und Betonwaren GmbH – INADEQUATEcannot be used in sewer construction due to very poor re-excavation properties
  • WBM-Flüssigboden by WBM-Flüssigboden GmbH – INADEQUATEcannot be used in sewer construction due to slow hardening, poor recyclability and high ammonia values

Three reached the finish line, two fell by the wayside

The winner with the grade GOOD (1.9) was Carbofill from the manufacturer Thomas Zement, which only has a weakness worth mentioning in the test of walkability after filling. In second place, very close behind, comes the RSS liquid floor from the FiFB (Forschungsinstitut für Flüssigboden) research institute, also with a GOOD (1.9) rating. The material only had difficulties with the filling of the shoring removal simulation. TerraFlow from Heidelberger Beton received a low score for “re-excavation capability”, a devaluation of 1.0 grade points, but is otherwise on a par with the best performers. Overall, TerraFlow achieved a SATISFACTORY (3.4) and thus third place.

The Terrapact material from Holcim Beton und Betonwaren could only be removed from the test trench with great effort and heavy equipment. The result was an INADEQUATE in the criterion of re-excavation capability, and thus was found to be not suitable for use in sewer construction. The WBM-Flüssigboden material, on the other hand, had a problem with the criterion of hardening. It could only have been built over after considerably more than 28 days. In addition, the MAK value for ammonia was exceeded for this product (MAK = maximum allowable workplace concentration) and the recyclability was also inadequate. The verdict of the testers: INADEQUATE, not applicable in sewer construction.

Awarding of certificates: How the evaluation graded the products

shrinkage test with flowable backfill in orange pipe segments

Supplementary laboratory tests provided the testers with a detailed picture of the properties of the candidate products.

The final scores in this IKT-Compare product test are based on the results from three main areas of evaluation: the 1:1 scale evaluations in the test pit and supplementary laboratory tests, in-situ investigations of the use of the product, and evaluation of the supplier‘s quality assurance system. The grade spectrum is based on the German school grading system and ranges from VERY GOOD (1.0) to INADEQUATE (6.0).

Evaluation weightings
The evaluation comprised a weighting of 85 percent for the performance tests and 15 percent for quality assurance for the overall grade. The performance tests results were weighted for the three phases of application of the products: “installation phase” (40 percent), “use phase” (30 percent) and “disposal phase” (30 percent). The 15 percent total for quality was made up from consideration of five aspects: the delivery note, self-monitoring, quality certificates, and any other conspicuous observations on quality – each contributing 20 percent of the assessment of quality assurance.

Unscored additional information supplements the hard test data: pH value of the material (installation), viscosity balance (average shear strength on the 1st and 2nd day), time required for installation, location of mixing unit, distance between mixing unit and IKT, number of deliveries (total 50 m³), material costs, pumping costs, testing costs (self-monitoring), disposal costs.

Much effort was expended in order to provide users with valuable insights

test stand with manhole and crossing pipes

Construction of the 1:1 scale simulated excavations in the test pit: five concrete manhole shafts, five plastic manhole shafts, five sewer pipes, five crossing pipes, ten shoring boxes – and 30 tons of steel to make the trench walls.

For this IKT-Compare product test “Flowable Backfill in Sewer Construction”, the test hall team divided the Institute’s 15-metre long, six-metre wide and six-metre deep large-scale test stand using 25 millimetre thick steel plates to create five test chambers. Exactly the same construction of concrete manhole shafts, plastic manholes shafts and shoring boxes, as well as main, transverse and longitudinal pipes were installed in each chamber. The man-hours for installation alone added up to many weeks. Added to this is the time spent by IKT structural engineer Dr Mark Klameth on the calculations for the installations. A total of 30 tonnes of steel were used. Then the suppliers came and pumped their Flowable Backfills into the compartments and the evaluations could begin.

Testing confirmed that Flowable Backfill has many advantages

All five materials flowed well into the trenches – a pleasure to watch as, like liquid lava (only not so hot), they glided elegantly into every corner, enclosed the pipes and manhole shafts, and filled the test stand up to the top. Satisfied faces were also to be seen on the construction sites that the evaluation team visited to gather in-situ impressions and experiences.

Extensive test programme

flowable backfill flowing from mixing truck into wheelbarrow

Start of the inspection programme: First samples taken during delivery

The extensive testing programme began during the installation of the Flowable Backfills: the product test team determined the consistency of the backfill, among other things, by means of a spreader gauge, checked the shear strength with a visco-balance, measured the pH value, filled the containers for a 3-segment cylinder test – which shows whether the suspension separates over time – and took samples for cube pressure testing, which determines the modulus of elasticity after seven days. This was followed by walkability tests, load plate compression tests and the cube compression tests mentioned above. In further testing during the use and disposal phases, the product testers examined the pipe bedding and the backfilling of the shoring removal simulation. The results of eluate tests allowed the scientists to assess the environmental compatibility of the materials. And the steering committee members evaluated the ability of the soil to be removed using a spade by picking up the spade themselves and comparing the materials directly.

The steering committee – support at all levels

man in black suit in auditorium

In regular steering committee meetings, the participants decided on the test requirements, among many other things.

The local steering committee is the highest decision making authority in each IKT-Compare test. Only wastewater network operators are entitled to participate. All fundamental decisions are taken by the steering committee. The following local authorities participated in the IKT-Compare test “Flowable Backfill in Sewer Construction” in terms of both its content and financing:

  • Technische Werke Burscheid (public utility company) as applicant/client
  • Abwasserbetrieb Troisdorf (local sewage operator)
  • Lippeververband (special purpose association) represented by Stadtentwässerung Hamm (sewer network operator)
  • medl, Mülheim/Ruhr (public utility company)
  • City of Gladbeck
  • City of Recklinghausen
  • SAL Stadtbetrieb Abwasserbeseitigung Lünen (local sewage operator)
  • Stadtentwässerung Düsseldorf (municipal drainage operation)
  • Technische Betriebe Solingen (municipal technical operations)
  • Wirtschaftsbetriebe Oberhausen (municipal enterprises)/City of Oberhausen
  • WSW Energie & Wasser, Wuppertaler Stadtwerke (public utility)

This project was generously funded and actively supported by the Ministry for the Environment, Agriculture, Nature and Consumer Protection of the State of North Rhine-Westphalia, Germany.

With exceptions, Flowable Backfill can be built over within 7 days

test rig for load plate compression test on flowable backfill

Under pressure: the load plate compression test was used to determine the modulus of elasticity of the installed Flowable Backfills.

A minimum value of 45 MN/mm² achieved in the load plate compression test is decisive for determining if hardened Flowable Backfill can be built over. The measured EV2 values (modulus of elasticity) reached this value within the first week for four of the five products tested. However, extremely high EV2 values can also indicate that the final strength of the flooring may be too high for re-excavation.

In addition to the laboratory tests at IKT, the Flowable Backfills were also installed in trenches at a test site in Burscheid. Here and during further construction site investigations, the basic handling of the materials under practical conditions was recorded and any differences with the installations witnessed in the IKT large test facility was also checked. These observations were considered as part of the scoring for quality assurance.

section of IKT compare seal with green and red writingThe IKT Product Test (Warentest) Seal

Product manufacturers and process providers who have taken part in an IKT product test can receive an IKT product test seal with the achieved result. This allows the quality of the product or process to be documented for customers.

more information about the “IKT-Warentest” seal

Quite OK: Quality assurance by contractors

In addition to the system tests of the Flowable Backfills in the test set-ups, the testers also examined the quality assurance provisions by the manufacturers. With few exceptions, the scores in this area show that the suppliers are making great efforts to ensure quality. But there is still a bit of room for improvement.

Special attention to meeting key performance criteria

The steering committee of the network operators defined early on the performance characteristics which must be met at all costs in order to ensure that a Flowable Backfill can be used in sewer construction. These concerned: the flowability in the installation phase, the build over capability in the utilisation phase and the re-excavation capability and potential for recycling in the disposal phase. Two out of five products proved to be defect-free in tests against all these criteria: Carbofill and RSS Flüssigboden. The remaining products, on the other hand, revealed visible or even serious defects, which in two cases led to the IKT-Compare test verdict “Inadequate”.

Quality assurance in the mixing plant is extremely important

In the test, the suppliers were asked to offer the products in such a way that their composition was clearly defined and that it was also possible to re-order them for future installations. Accordingly, the suppliers were free to choose the soil material to be used. In at least one case, however, an unsuitable soil material (organic matter, ammonia release, poor build over capability) was used in the performance tests. The network operators represented in the steering committee see the suppliers/manufacturers as responsible here for reliably determining the quality of the substances and soils used in their product and making this information transparent. Soil management and quality assurance in the mixing plant where the Flowable Backfill is produced are therefore of particular importance.

Conflicting objectives: need to firm up quickly, but not be too firm for later re-excavation

person with work shoes standing on hardened flowable backfill

Quickly walked on, quickly built over, but later removeable: the demands on Flowable Backfills are high.

Obviously, for many suppliers there is a conflict of objectives between rapid walkability and buildability and the later re-excavation capability (using a spade) of the material. Only one provider (RSS Flüssigboden) succeeded in fulfilling these criteria in the system tests with very good or good results throughout. The four remaining suppliers showed clear deficiencies in at least one of these criteria in the test.

Pulling out the shoring can lead to massive surface fractures

Pert of the evaluation involved the removal of simulated shoring from the test trenches. In individual cases, pulling the shoring led to massive surface fractures, which can lead to uncertainty at the construction site about the success of the backfilling process and necesitate. However, in the testing, the observed cases did not show any effects on the load situation in the subsoil. Where fractures did occur, the manufacturers are required to adapt the materials accordingly or to specify suitable times for pulling the shoring.

Quality assurance on the construction site

concrete manhole in test stand filled with flowable backfill

Appeal to users: check the most important quality issues on the construction site!

The test results show that there are important assessment criteria that should be checked in construction site practice in the course of internal and external monitoring of a Flowable Backfill installation. This applies in particular to the flowability, walkability, build over ability, and bedding properties as well as the lifting of shoring. Furthermore, the manufacturer should provide the composition of the materials used, including the soil material, in a transparent and verifiable manner. It may also be appropriate to check the homogeneity of deliveries to site, i.e. the extent to which variations in properties between batches can be observed.

In the run-up to this product test, 16 manufacturers of Flowable Backfill were researched who offer their products for use in sewer construction. However, only six suppliers were in a position to offer a nationwide service such that the product could be used in North Rhine-Westphalia for both the test fields in Burscheid and in the performance tests at IKT in Gelsenkirchen. Moreover, one of these products was not pumpable at the time of the award of the contract, so ultimately only five products were used and compared in the system tests. Consequently, an expansion of the delivery areas for more products and also new and further developments of products are desirable. IKT testing could then underpin their quality.

Possibility for retesting

Not been involved in this product test? Your material can do that too? Then there is an opportunity to prove it in follow-on testing – the same tests under the same conditions with the same evaluation criteria. At the end there is a score and a place in the results table. And if you want, you can also get a seal.
Talk to us!

Improving the image of Flowable Backfill

The IKT-Compare product test shows that in principle, Flowable Backfill is already a suitable technology for sewer construction. Not for all products, but compositions can be optimised, and at some point the ideal case will become the norm.

bearded man with glasses, suit and tie

Serdar Ulutaş, Head of IKT-Compare, presents the results in detail.

IKT-Compare product test “Flowable Backfill in Sewer Construction”
to the results table of this product test (in English) (PDF)
Download the product test report (in German) (PDF)

Contact persons

Dipl.-Ing. (FH) Serdar Ulutaş, MBA
Head of IKT Product Testing
phone: +49 209 17806-32
e-mail: ulutas@ikt.institute
Dr Iain Naismith
IKT Project Manager UK and International
phone: +44 7983 605219
e-mail: naismith@ikt.institute

Neutral and independent: The IKT-Compare Product Tests

parallel sewer pipelines on bottom of huge test stand

In the independent IKT-Compare products tests, products or processes are tested comparatively under identical, reproducible conditions.

The aim of the IKT-Compare products tests is to provide network operators with reliable and independent information on the characteristics of products and processes available on the market. Details in process descriptions and advertising information of the providers are subjected to independent and neutral testing by the IKT-Compare products test.

The focus is on the suitability of products under long-term operating conditions. In particular, stresses occurring during operation are investigated that the products will be exposed in practice for decades.

Today, the warranty period for sewerage technology products is a maximum of five years. This is a very short period of time compared to the intended useful lives. Of particular disadvantage for clients are damages that only occur after the warranty period has expired. Recourse to the supplier is only possible in the rarest of cases. This results in a considerable financial risk for the network operators, which can be reduced by the comparative IKT-Compare products tests.

An IKT-Compare products test is always overseen by a group of network operators, the steering committee. This steering committee decides in regular meetings on:

  • the selection of products or processes for the first test series
  • the construction or maintenance task for the use of the products or processes in the test
  • the relevant performance targets and quality requirements
  • the scope and focus of the evalution programme
  • the exchange of information with the suppliers of products or processes
  • the evaluation and publication of the results

The actual testing and documentation of the results is carried out by IKT as an independent institute. Within the scope of the testing, IKT is responsible in particular for the engineering development and implementation of the test setups and the test programme. Decisions in this respect are made in direct coordination with the steering committee.

more about IKT-Compare products testing
to the downloads of the IKT-Warentest reports


IKT Compare: Can Short Liners Repair House Connections?

man in manhole installing short liner

How do short liners perform? IKT figured it out in its latest IKT Compare project.

Short liners are often the first choice for repairing local damage in house connections. But, can they deal with seriously damaged pipes? The results of the new IKT-Compare project “Short Liner for House Connections” are now available.

IKT institute has found in its most recent IKT-Compare project that in principle short liners (also referred to as patch or point repairs) can make good quality repairs to house connection pipes, even when the pipe is severely damaged. Eight short liner systems were tested and achieved scores ranging from “VERY GOOD” to “SATISFACTORY”. The evaluation did find significant differences in performance between the systems that were examined.

Twinbond Liner was the best performer with a score of VERY GOOD (1.2). Second place went to epros DrainPacker (Trelleborg) also graded VERY GOOD (1.4). Bodenbender Point-Liner-System (1.7), Berolina Repair System (2.5), Cosmic TopHat system (2.5) and MC Konudur LM-Liner (2.5) each received a GOOD grade. Alocit short liner (2.7) and I.S.T. Spot Repair System (2.9) were graded SATISFACTORY.

The project has been undertaken in co-operation with twelve sewer network operators which wanted to understand the strengths and weaknesses of this widely used technology. It has been funded by the North Rhine-Westphalian Ministry of the Environment and the network operators.

Download table of results
Download product test report (German)

Tough testing of short liners

two men installing sewer pipes in testing facility

Deliberate defects: IKT has installed eight test sections with a total of 64 cases of damages in its large test pit.

A rehabilitation using a short liner should be able to restore the structural stability of a pipe, secure its hydraulic performance and seal a damaged area. For this reason, the IKT Compare team and the network operators involved placed particular emphasis during testing on the water tightness, operational reliability and structural stability of the rehabilitation. The particular focus was resilience external water pressure.

Test set-up damage scenarios

For this project IKT built eight identical 1:1 scale rigs, in its large-scale test pit (15m by 6m by 6m), into which suppliers installed their short liners. Each rig comprised a length of sewer to which were attached one house connection pipe on the same level as the sewer pipe and two house connection pipes from a higher level. The house connection pipes were prepared with defined areas of damage, including milled patterns of cracks, the removal of some or all of the joint seals and broken sections. A total of 64 damage patterns were produced – eight in each of the eight test rig setups.

members of steering committee looking at test set-up

Two up, one down: the test set-up.

These patterns of damage were arranged as follows:

  • Test Setup I (the lower house connection pipe, to which a 2m head of external groundwater was subsequently applied): cracks, a broken joint, a radially displaced joint and a joint displaced at an angle
  • Test Setup II (the two higher house connection pipes, to which a 1m head of groundwater pressure was subsequently applied): a defective change of pipe material, defective change of pipe diameter and material from cast iron DN 150 to PVC DN 125, a defective change of pipe diameter and material from clay pipe DN 150 to PVC DN 125, and a break in the joint of a 45 degree bend

Following installation of the eight different short liner systems into separate test rigs, an extensive testing programme began, starting with initial visual inspection and leak tests. This was followed by short-term and long-term external water pressure tests, high-pressure jetting at different pressures and using different types of nozzle, simulated backing-up of water, changing groundwater levels, and cleaning with rodding devices.

Frequent visual inspections and leak tests were undertaken as the programme progressed. Finally, when the test rigs were exhumed from the test-pit, the cross-section reduction was measured and the adhesive tensile strength and ring stiffness of the installed liners were assessed.

Grading of performance

construction site in front yard

In-situ tests: lab tests were validated through in-situ observation of the same systems being installed at actual construction sites.

In addition to physical tests, the QA/QC procedures were examined. The laboratory results were validated through in-situ observation of the same systems being installed at actual construction sites. The final scores in this IKT Compare test are based on these three evaluations. The range of grades applied is from VERY GOOD (score of 1.0) to INSUFFICIENT (score of 6.0).

Weighting of scores: Water Tightness counts for the most

To derive the final scores the results of the 1:1 scale testing system tests were given a 85% weighting and the results of the QA/QC evaluation 15%. For the 1:1 scale test score, the three test criteria were weighted as follows: “water tightness” (60 percent), “operational reliability” (20 percent) and “structural stability” (20 percent).

two men inspecting repaired sewer pipes

Ongoing observation. IKT testers regularly check the installed short liners for leaks.

The assessment of QA/QC comprised five criteria: the installation manual, the available training courses, the system’s DIBt (German Government’s approval body) approval, external production monitoring, and a comparison between the installations observed in the laboratory and in the field. The results for each criteria were given a 20% weighting in the final QA/QC score.

In addition to the test criteria used to derive the comparative scores of the systems, supplementary information was collected and presented that would be of interest to the end user. These include results from internal pressure tests undertaken after the rigs were excavated and the adhesive tensile strengths of the liner bonding to the host pipe. The preparatory measures undertaken by the installer, such as initial inspection, substrate preparation and cleaning, were documented. Also presented are: the number of on-site working days, the number of installation staff, the time required for preparatory work and installation, and the costs.

The Steering Committee – twelve cities

Members of the Steering Committee for the IKT Compare project “Short Liner for House Connections” are the following German cities: Billerbeck, Burscheid, Dortmund, Duisburg, Düsseldorf, Gelsenkirchen, Göttingen, Hagen, Herne, Rheda-Wiedenbrück, Schwerte, and Arnhem from the Netherlands.

What the systems can do

test rigs of house connections in testing facility

Repair objective: to seal damaged house connections.

In this IKT Compare project, the system suppliers demonstrated that serious damage to house connections can be reliably sealed using short liners, including breaks, cracks, misalignments and deflections. In particular, the Twinbond and Trelleborg systems proved to be the most reliable under permanent groundwater load, jetting, simulated backflow events and changing groundwater levels. For this they were deservedly awarded the score of 1.0 for water tightness.

Special Challenges

In principle, it was also shown to be possible to seal the changes in nominal diameter and pipe material in Test Setup II. However, four of the systems came up against their performance limits here, showing weak points, which led to infiltration. In one case, gushing water was visible immediately after installation. Therefore, changes in diameter and material require special attention during installation.

Results of Test Setup I

All eight short liners showed very good to satisfactory results for the four damage patterns in Test Setup I: cracks, broken joint, radially displaced joint and joint displaced at an angle. No infiltration was observed during the whole test period. However, about half of the systems showed visual abnormalities in the form of moisture and/or discoloration at some locations, but without the formation of droplets.

Structural stability assured

Adhesion test on short liner

Adhesion test

The structural stability testing of the short liners showed that they basically have reliable adhesive and load-bearing performance. For products with full-surface bonding of the liner to the host pipe, hardly any abnormalities were observed, i.e. no crack formation, no excessive deformation, no stability failure nor large-surface loosening of the adhesive bond. Five systems showed partial loosening of the adhesive bond at points of changing diameter or pipe material, albeit without any consequences.

The Cosmic system is not intended to bond over the full-surface, only at the start and end of the liner. However, the supplier was able to submit a static proof which confirmed the structural stability of the short liner observed in the test.

Operational activities

water from high-pressure-jetting splashing on test site

High-pressure jetting did not affect the short liners.

The test scenarios simulating sewer operation, such as high-pressure jetting, water backing-up in the pipe, and changing groundwater levels, had no significant effects on system performances.

Good QA/QC

There were no issues with quality assurance: seven out of the eight systems fulfil all the criteria for quality assurance and receive a grade of 1.0. The Cosmic system does not have a DIBt approval and so gets a grade of 2.0.


In conclusion the IKT Compare project “Short Liners for House Connections” has demonstrated that short liners can renovate even severely damaged sewer pipes. However, changes in diameter and material require special attention during installation as they might cause serious problems. It is important to select the right system for the task, to understand the limitations of individual systems, and apply the necessary QA/QC before, during, and after installation.

Download table of results
Download product test report (German)


IKT ‑ Institute for Underground Infrastructure, Germany
Serdar Ulutaş, MBA, Dipl.-Ing. (FH)
phone: +49 209 17806-32
email: ulutas@ikt.institute

IKT Compare: How good are products really?

three men preparing defined damages on the test rigs

Defined damages: preparing the test rigs

The objective of IKT Compare projects is to provide network operators with reliable, neutral, and independent information on the strengths and weaknesses of products and methods in sewer technology. IKT Compare projects are always undertaken in collaboration with network operators. Their representatives form a steering committee which takes all important decisions on how to test the products.

At the core are tests under realistic service life conditions such as traffic and ground loads, groundwater pressure and high-pressure jetting.
Each IKT Compare project is accompanied by a steering committee set up of network operators. The committee meets regularly and takes decisions on:

  • products to be tested
  • scope of the test programme
  • test criteria
  • test set-up
  • final grading and assessment of the test results

The actual testing and documentation of the results are carried out by IKT, as a neutral and independent institute. As a result, network operators are provided with independent, practice-related, and technically well-founded information on the strengths and weaknesses of products, their applications and limits.


Manhole Rehabilitation: Comparative testing of 13 different methods

manholes in IKT's large-scale test facility

On-site installation conditions simulated in IKT’s large-scale test facility

Can wastewater manholes be rehabilitated so that they remain permanently watertight? What are the benefits and the drawbacks of mortar coating, plastic coating and lining. What quality can be expected? This first comparative product test in this field gives you the answers!

“Now for the manholes” – this is a train of thought in the repair/rehabilitation departments of many wastewater network operators. There is, indeed, little point in rehabilitating wastewater pipes without paying attention to the numerous defective manholes. This is particularly true in water infiltration zones, since a really watertight sewer network can only be achieved provided the manholes are also rehabilitated.

Under test: thirteen manhole rehabilitation methods

Which of the many manhole rehabilitation methods should we choose? Which one will seal reliably and durably? Which is suitable in which situation, and which are not suitable? Thirteen commercially available methods have now been analysed in IKT‘s “Manhole Rehabilitation” Comparative Test. The results range from GOOD to ADEQUATE, with one method failing the test.

Comparative Test: Manhole Rehabilitation

Read the whole article with all test results (PDF, 10 pages)


Serdar Ulutaş
Dipl.-Ing. (FH), MBA

T: +49 209 17806-32
E: ulutas@ikt.de


Comparative assessment of innovative inspection procedures and equipment for site drainage systems

Sewer camera in use

Sewer camera in use

This research project involves the development of a test programme to comparatively test and evaluate the inspection procedures and equipment currently available for site drainage systems. Practical experience is to be gathered in pilot deployments in cooperation between the Meyer-Entsorgung disposal company and the City of Osnabrück. In addition, general recommendations for action to provide both the public and system operators with assistance prior to the actual inspection are to be drafted, based on experience from the City of Osnabrück. The project is receiving funding from the German Federal Environmental Foundation (DBU).


“Comparative assessment of innovative inspection procedures and equipment for site drainage systems and recommendations for action for preparation of the inspection (Phase I: Actual-condition survey, test programme and recommendations for action)”

Project management

IKT ‑ Institute for Underground Infrastructure gGmbH

Project participants

  • August Meyer Entsorgung – Technische Dienstleistungen GmbH & Co. KG (disposal organisation)
  • City of Osnabrück
  • Client

    German Federal Environmental Foundation (DBU)


    Christoph Bennerscheidt

    T: +49 (0) 209 17806-25
    E: bennerscheidt@ikt.de


IKT Comparative Test “Odour filters”

What will help against nasty smells from sewers?

What will help against nasty smells from sewers?

In the summer months, in particular, odour emissions from sewers cause odour nuisances and thus higher levels of complaints from residents. Sewer-system operators are in general obliged to find a remedy for such problems.

Odour filters installed in waste-water manholes are coming into increasing use. In addition, further products which release special active ingredients in the waste-water manhole shaft are also used. The aim of this Comparative Test was that of testing the odour filters for waste-water manholes available on the market together with the participating sewer-system operators for their fluid permeability, cleaning performance and easy usability, and to perform a comparative assessment of their quality. Products which release special active ingredients into the waste-air leaving such waste-water manholes for the suppression of such odours were also tested.


IKT Comparative Test “Odour filters”
with supplementary testing of other products for use in waste-water manhole shafts in case of odour nuisance


(German versions only)
Table of results
Test Report (127 pages)
Short Report (31 pages)


  • Kiel (capital of state of Schlewig-Holstein) – urban drainage utility
  • City of Ahaus
  • City of Frankfurt am Main
  • Hamm urban drainage utility (Lippeverband water authority)
  • Hannoversch Münden urban drainage utility
  • Ludwigshafen urban drainage utility
  • Cologne urban drainage utilities
  • Düsseldorf urban drainage utility
  • Magdeburg municipal utilities
  • Leverkusen municipal utilities
  • Burscheid municipal utilities

Comparative Test participants

  • University of the German Federal Armed Forces, Munich, Institute of Water Resources
  • University of Stuttgart, Institute for Sanitary Engineering, Water Quality and Solid Waste Management (ISWA)
  • University of Kassel, Department of Urban Water Management within the Institute for Water, Waste and Environmental Management (IWAU)


Thomas Brüggemann

T: +49 (0) 209 17806-18
E: brueggemann@ikt.de