Frequently asked questions

Siebert + Knipschild tests a wide range of plastics and composite materials for a wide variety of applications. These include thermoplastics such as PE, PP and PVC, thermosets such as epoxy and polyester resins, and elastomers. In addition, we test composite materials such as glass-fibre-reinforced plastics (GFRP) and carbon-fibre-reinforced plastics (CFRP), as well as other composite materials.

Tests can be carried out on raw materials, semi-finished products, pipe materials, welded joints or finished components. Our customers come from sectors including industry, environmental and plant engineering, vehicle manufacturing, construction, medical technology and consumer goods.

Depending on the specific requirements, we provide support ranging from material characterisation and product approval through to failure analysis and quality assurance.

We offer mechanical, chemical, thermal and optical tests for plastics, composites and products and components manufactured from them. These tests enable, amongst other things, the reliable assessment of strength, stiffness, heat and chemical resistance, material properties and the composition of materials.

Our services include, for example, flexural tests, static and breaking load tests, ultrasonic measurements, 3D microscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), melt flow rate determinations, and investigations into chemical and thermal resistance. In addition, we carry out damage analyses and prepare material reports, and conduct tests in accordance with standards, regulations and individual customer specifications.

A comprehensive overview of our accredited testing methods can be found under ‘Services’ on our website. Should you require a specific test that is not listed within our accredited scope, please do not hesitate to contact us. Thanks to our flexible accreditation, we can adapt many methods to individual requirements and, where appropriate, incorporate them into our accredited scope. Tests outside the accredited scope are also possible, depending on the specific task at hand.

Yes, many investigations are carried out on individual parts or components that are already damaged, for example, if a component has failed unexpectedly or if the cause of damage needs to be determined. Materials that were already damaged can also be examined.

It is important to distinguish whether a damage analysis is required to determine the cause of failure, or whether the material properties of the originally undamaged material are to be determined. We select the appropriate examination and testing methods depending on the specific requirements. For a well-founded assessment, information on the application, the load conditions, and any available documentation or data sheets is often helpful.

Yes, material analyses and identification procedures can be used to verify whether a material meets the specified requirements and is in fact made of the expected material. These tests can examine the type of material, its composition and its characteristic properties.

To ensure the assessment is as clear-cut as possible, it is helpful to provide any available data sheets, specifications or other reference documents. If no such information is available, the comparison can be carried out on the basis of available technical literature or using reference samples, for example of new material.

The test helps to identify material mix-ups, deviations from specifications or quality-related anomalies at an early stage. This ensures that materials and components are suitable for their intended use and meet the required standards.

Yes, different plastics can be compared in a targeted manner. This involves examining and comparing their mechanical, thermal, chemical and physical properties. This makes it possible, for example, to assess which material is better suited to a particular application or whether alternative materials offer comparable performance.

Depending on the specific question, properties such as strength, stiffness, elongation behaviour, temperature resistance, density, chemical resistance or ageing behaviour, amongst others, can be compared. Plastic-based composites can also be compared with one another.

Yes, different plastics can be compared in a targeted manner. This involves examining and comparing their mechanical, thermal, chemical and physical properties. This makes it possible, for example, to assess which material is better suited to a particular application or whether alternative materials offer comparable performance.

Depending on the specific question, properties such as strength, stiffness, elongation behaviour, temperature resistance, density, chemical resistance or ageing behaviour, amongst others, can be compared. Plastic-based composites can also be compared with one another.

Yes, in many cases it is possible to determine whether a plastic shows signs of ageing. Plastics change over time due to factors such as UV radiation, heat, moisture or contact with chemicals. These factors can alter the mechanical, thermal, chemical or optical properties of the material.

Various testing and analytical methods are available for assessing ageing processes. For example, micro-cracks, material degradation or changes in material properties can be detected.

However, whether ageing has occurred and to what extent depends heavily on the specific material and the operating conditions. Tests are particularly informative when comparative data from an unaged material or reference samples are available. This allows changes and the degree of ageing to be assessed accurately and specifically.

That depends on the test method chosen. A basic distinction is made between non-destructive and destructive testing methods.

In non-destructive testing, for example using ultrasonic or visual inspection, the component remains intact and can subsequently be reused. Destructive testing, such as tensile, compression or fracture tests, on the other hand, deliberately subjects the component to stress until it is damaged or fails. In this way, important information about material properties, strength and load-bearing capacity can be determined.

If only a small amount of test material is available, a decision must be made on a case-by-case basis as to what extent non-destructive testing or tests requiring only a small amount of material are sufficient to provide reliable results.

To assess the quality and suitability for use of a pipe liner, particular attention is paid to testing its mechanical properties, the wall thickness required to bear structural loads, its watertightness and the correct curing process. These properties are crucial in determining whether the installed liner meets the planned structural and operational requirements. The relevant requirements and tests are described, amongst other places, in DWA Worksheet DWA-A 143-3.

Typically, parameters such as flexural strength, flexural modulus of elasticity, ring stiffness, wall thickness and watertightness are examined. In the event of anomalies or where target values are not achieved, supplementary tests – for example, on curing quality or residual monomer content – may be advisable. This enables an assessment of whether the long-term performance and the intended service life of the pipe liner are guaranteed.

The testing of pipe liners depends on the specific requirements and the contractual and regulatory specifications. Typical tests include, amongst others, the determination of wall thickness, flexural tensile strength, flexural modulus of elasticity, watertightness and long-term behaviour.

In addition, specialised tests may also be carried out, for example to assess chemical resistance, laminate structure or load-bearing capacity under realistic operating conditions. Where necessary, complete system tests are carried out to assess the interaction between the liner, fittings, end connections and other components.

Pipe liners are tested in accordance with various standards and regulations. A distinction is made between system standards and test standards.

System standards, such as DIN EN ISO 11296-4 or DWA-A 143-3, specify the requirements that a pipe lining system must meet and the properties that must be demonstrated. Test standards, on the other hand, describe how these properties are tested, for example wall thickness, flexural strength, flexural modulus or leak-tightness.

Put simply: the system standard specifies what must be demonstrated, whilst the test standard describes how this demonstration is carried out.

Which standards are to be applied in each individual case depends on the specific pipe lining system, the area of application and the contractually agreed requirements. Siebert + Knipschild carries out tests in accordance with the applicable standards, regulations and project-specific specifications.

The three-point bending test is used to determine the mechanical properties of a pipe liner. It assesses the stiffness, load-bearing capacity and deformability of the installed liner material. The test is carried out in accordance with the requirements of DIN EN ISO 178 and DIN EN ISO 11296-4.

For the test, a specimen is taken from the installed pipe liner. This is placed on two supports and then loaded centrally with a compression fin. The load is applied until the specimen breaks or until the required measurement values have been recorded.

Among other things, the test determines the flexural modulus of elasticity (stiffness of the material), flexural stress (load-bearing capacity of the material), elongation under load and the statically load-bearing wall thickness.

The results enable the properties of the liner to be characterised. It is also possible to verify whether an installed liner meets the minimum requirements specified in approvals, regulations or tender documents.

The watertightness of a pipe liner is tested using the watertightness test in accordance with DWA-A 143-3. This test examines whether water can penetrate the pipe liner laminate.

For the test, a test fluid is applied to a defined area of the sample. At the same time, a negative pressure of 0.5 bar is created on the underside of the sample. If no water penetrates the laminate within 30 minutes, the sample is deemed to be watertight.

The crown pressure test is used to assess the ring stiffness of a pipe liner. Unlike the three-point bending test, which examines only a section of the wall, this test is carried out on a closed ring and thus reflects the behaviour of the liner as a complete system.

For the test, a ring-shaped section of the hose liner is loaded in a testing machine. The forces generated and the deformation of the ring are recorded and analysed.

Important parameters such as the initial ring stiffness, the circumferential modulus of elasticity and the statically load-bearing wall thickness can be determined from the measurement results. These values can also be used to assess whether the hose liner meets the requirements of the relevant approval or product specification.

Plastics do not merely deform immediately under load; they can also continue to deform slowly over a longer period of time. This behaviour is known as creep. The creep tendency describes the extent to which a pipe liner is prone to this time-dependent deformation.

In the 24-hour creep test, a liner sample is tested under a constant load for 24 hours. The test measures how the deformation develops over time. The determined creep tendency value is expressed as a percentage.

The test serves as short-term evidence of the hose liner’s long-term behaviour. It simulates the initial phase of a long-term test lasting 10,000 hours, on the basis of which key parameters for the structural analysis are determined. If the required limit value is met, this indicates that the tested product possesses the same properties as the system which was extensively tested for its long-term behaviour as part of the type approval process.

A low creep tendency is an indication that the pipe liner retains its shape and load-bearing capacity over the long term, even under continuous loading.

The glass fibre content has a significant influence on the mechanical properties of a hose liner, particularly its strength and stiffness. To determine this, a sample of the liner is heated to temperatures in excess of 600 °C. This process is known as the determination of ignition residue or calcination.

During this process, resins and other organic components burn away completely. What remains are the non-combustible components, primarily glass fibres and any mineral fillers that may be present.

By comparing the weight of the sample before and after the test, the proportion of organic and inorganic components can be determined. The remaining ash residue also provides information on the layer structure and material composition of the hose liner. This makes it possible to verify whether the liner’s structure complies with the requirements and specifications.

To determine the resin system used, an infrared spectral analysis (FTIR) is usually carried out. In this process, the sample is analysed using infrared radiation. Due to its chemical structure, each resin has a characteristic spectrum which can be used for identification, much like a ‘fingerprint’.

By comparing the measured spectrum with reference data, it is possible to determine which resin system was used. For example, polyester resins (UP), vinyl ester resins (VE) and epoxy resins (EP) can be distinguished from one another.

The test is primarily used for identity verification. It is employed, for example, to verify material specifications or to investigate anomalies identified in other tests in greater detail. This makes it possible to check whether the resin used corresponds to the specified material.

Determining the residual styrene or residual monomer content serves to assess the degree of curing of hose liners. It is used in particular for liners made of polyester resin (UP) or vinyl ester resin (VE), in which styrene or other reactive diluents or monomers are used.

During curing, these components are incorporated into the polymer structure. The remaining monomer content therefore serves as an indicator of the liner’s degree of curing: low levels suggest that curing is largely complete, whilst elevated values may indicate incomplete cross-linking of the resin.

For the analysis, a material sample is ground up and the remaining monomers are extracted using a suitable solvent. The content is then determined using gas chromatography.
When styrene is used as a reactive diluent, technically complete curing is usually assumed to have taken place when the residual styrene content is approximately 2 per cent or less. For other reactive diluent systems, there are currently no specifications in the regulations regarding the permissible residual monomer content.

DSC analysis (Differential Scanning Calorimetry) can be used to investigate the thermal behaviour of plastics and resin systems. In the field of trenchless sewer rehabilitation, it is used in particular with epoxy resin systems to assess the curing status of a pipe liner.

For the analysis, a small material sample is heated in a controlled manner. The testing instrument measures the amount of heat absorbed or released by the material. Even very small sample quantities are sufficient for the analysis.

Of particular interest is the glass transition temperature (Tg), which is determined from the DSC heat flow curve. It is a characteristic parameter of the resin system and allows conclusions to be drawn about the degree of curing of the resin system. In the case of epoxy resins, the determined Tg is frequently used as evidence of sufficient curing, similar to the determination of residual monomer in UP or VE resin systems.

Furthermore, DSC analysis can provide indications as to whether curing is fully complete or whether unreacted resin components are still present in the material. It is therefore also suitable for quality assurance in other epoxy resin applications.

Dynamic mechanical analysis (DMA) is a testing method used to investigate the mechanical behaviour of plastics and resin systems. It is used in particular in the field of trenchless sewer rehabilitation to evaluate material properties such as the flexural modulus of elasticity and the curing state of a resin system.

During the test, a small specimen is subjected to a very low, periodically recurring load. Unlike many other mechanical tests, the specimen is not loaded to the point of failure.

A particular advantage of DMA is that even very small specimens can be analysed. It is therefore suitable, for example, for service line liners, where the sample material is often insufficient for a conventional three-point bending test.

The test provides information on the stiffness, deformation behaviour and degree of curing of the material. It can also be used when an assessment via DSC or residual monomer analyses is not possible or is of limited significance, for example in the case of silicate resin systems whose composition makes such characterisation difficult.

A failed test result means, first and foremost, that at least one measured parameter did not meet the specified requirements. This indicates a deviation from the specified requirements.

However, the test result alone does not allow us to determine what impact this will have on the installed liner. For a well-founded assessment, factors such as the nature and extent of the deviation, the properties affected (e.g. structural integrity, watertightness or curing), further test results and any anomalies observed on site must be taken into account.

Only a comprehensive analysis of all results enables a reliable technical assessment. It is therefore advisable to contact the testing institute directly in the event of a failed test result. Test specimens are retained by Siebert + Knipschild for at least three months.

If contractually agreed minimum requirements are not met, this initially constitutes a deviation from the performance due and therefore, in principle, a defect. However, any further assessment should take the sampling process into account.

Initial samples are often taken outside the installation site, for example in a manhole. They are therefore not necessarily representative of the installed pipe liner. Samples taken directly from the installation site, on the other hand, are representative of the installed product.

If the required parameters are not met in an initial sample, further tests are therefore usually carried out. This may include, in particular, a second sampling from the installation site. The aim is to determine with certainty whether there is a defect in the installed liner or whether it transpires that the contractual requirements are met in the installed state.

A failed test result initially simply means that a requirement stipulated in the contract, by technical specifications or by standards has not been met. Whether this constitutes a defect leading to rectification or even removal depends on the specific contractual relationship, the agreed requirements and the nature of the deviation identified.

Even when the VOB/B (German Regulations on the Award and Execution of Contracts for Construction Works) is applied, a failed test result does not necessarily lead to the liner being removed. The decisive factors are which requirements were agreed and what impact the deviation has on the system’s fitness for purpose, stability or durability.

In cases of doubt or where the technical circumstances are complex, an independent expert assessment may be required to make a professional judgement on the appropriate course of action.

A slight undershoot of mechanical performance values generally constitutes a deviation from the required minimum values. If the performance values from a DIBt approval are contractually agreed, these must generally be complied with. However, the consequences of the deviation depend on the specific contract, the client’s requirements and, where applicable, a subsequent technical assessment. The test report documents the measurement results; the assessment of the consequences is carried out by the parties involved in the respective project.

A wall thickness that falls short of the required specification means, first and foremost, that a measured value deviates from the required specifications. As wall thickness is usually both technically relevant and a contractually agreed component of the work, this may constitute a defect. The consequences of this depend on the contractual requirements, the extent of the deviation and its impact on the component’s function. However, a deviation below the required thickness does not automatically mean that the component must be replaced or removed. The assessment should always be made on a case-by-case basis.

The flexural modulus describes the stiffness of a pipe liner. Put simply, it indicates how much the material deforms under load. The higher the flexural modulus, the less a test specimen yields under load.

If the required value is not achieved, the liner is, in principle, less rigid than intended. This can affect its structural performance, particularly if other parameters are also out of the norm.

Flexural strength describes the load-bearing capacity of the material up to the point of failure. It therefore indicates the forces that the pipe liner can withstand before damage occurs.

If the measured value is below the required target value, this may indicate that the liner has, for example, material deviations, variations in wall structure or incomplete curing.

For a reliable assessment, the other test results and the project-specific requirements should always be taken into account.

Both results are relevant, as they test different characteristics.

The on-site leak test assesses the refurbished pipe system as a whole under actual installation conditions. Among other things, it checks connections, transitions and the watertightness of the entire pipe run.

The laboratory test, on the other hand, specifically examines a sample taken from the system for material defects, imperfections or air pockets within the laminate. This allows weak points to be identified which might otherwise remain undetected during a system-wide leak test.

A typical example is wear layers or films, which are deliberately perforated in the laboratory. This tests whether the actual laminate remains permanently watertight even if the surface is damaged.

Passing a leak test on the installation therefore does not automatically confirm the quality of the installed laminate. It cannot replace or override a failed laboratory test result. Both tests provide different, complementary insights into the quality of the system.

If test results are inconclusive or require further technical assessment, supplementary investigations may be advisable. Typical reasons for this include unusual mechanical properties, indications of incomplete curing, or the question of whether a construction product is suitable for its intended use despite identified deviations.

Depending on the specific issue, additional tests – such as DSC, DMA, spectral analysis, residual styrene or creep tendency tests – can provide valuable information. They help to narrow down the causes of anomalies and to assess the effects of deviations from a technical perspective.

The dynamic load test (DLT) is a test procedure in accordance with DIN 3603 designed to verify the resistance of pressure pipe systems to water hammer and continuous loading. The test examines not just a single component, but the entire pipework system under realistic operating conditions.

The test simulates recurring pressure and load cycles, such as those that may occur during subsequent use. The aim is to demonstrate that the pipework system continues to function safely and reliably even under adverse operating conditions.

Typical load situations include sudden pressure rises or drops (pressure surges), the switching on and off of pumps, the rapid opening or closing of valves, power cuts followed by the failure of pumps or gate valves, and other operational events that can lead to significant pressure fluctuations.

The test thus specifically simulates worst-case scenarios such as those that may occur during subsequent operation. In principle, all systems, components and materials intended for use under such conditions can be tested. These include, for example, pipe joints, flanged joints, couplings, branch connections, connection fittings, as well as bends and other fittings in the piping system.

The pressure pipe load cycle test is a practical testing method for pressure pipe systems. Its distinctive feature is that it is the only system test of its kind to simulate the actual alternating pressure loads that may occur later during operation, for example due to pump cycling, pressure surges or recurring load cycles.

Whilst many suitability tests and approval requirements examine individual product properties such as strength, leak-tightness or material characteristics, the DLT assesses the interaction of the entire pipework system under dynamic loading. In doing so, typical operating conditions are realistically simulated and the long-term stress on the system is evaluated.

The test thus fills an important gap: the load cycles occurring during practical operation are among the most critical stresses on a pressurised pipework system, yet they are not covered, or only to a limited extent, by many other tests and approval requirements. The DLT therefore provides additional insights into the operational safety and durability of a system under realistic operating conditions.

The pressure pipe load-cycle test is carried out in accordance with DIN 3603. The standard governs the testing of rehabilitated or repaired pressurised sewer pipes. It specifies how to test, under realistic pressure-cycling conditions, whether an entire pipework system is permanently resistant to pressure surges and safe to operate. In doing so, it assesses not only individual components but the entire system, including all connections and joints.

Material properties describe the characteristics of an individual material, such as its strength, stiffness or durability. However, the actual performance of a pressurised pipework system is determined by the interaction of all its components.

In addition to the pipe material, joints, flanges, couplings, seals, valves and the operating conditions also influence the safety and service life of the system. Pressure fluctuations, pressure surges, temperature changes and cyclic loads can significantly affect the behaviour of the entire system.

For this reason, system tests carried out under realistic operating conditions are often more informative than an analysis of material properties alone. They demonstrate how the complete pressure piping system behaves in practical use and where potential weak points lie.

The dynamic load test can be used to test a wide range of products and systems that are subjected to alternating pressure loads in pressure pipework. These include, in particular, pressure pipe liner tubes, GRP pressure pipes, connection systems, flange joints, fittings, sealing sleeves, repair systems and other components of pressure pipework.

The test is suitable for complete systems as well as for individual components. Through the realistic simulation of pressure cycles and pressure surges, products can be assessed under typical operating conditions.

In principle, not only the products mentioned above but also other pipework systems and components can be tested, provided that they are exposed to comparable cyclic pressure loads or pressure surges during subsequent use. The DLT thus enables practical verification of the long-term durability and operational safety of a wide variety of pressure pipework systems.

Yes, custom components can also be tested using the dynamic load test. The Dynamic Load Test is not limited to standardised pipe systems. In addition to pressure pipe hose liners, GRP pressure pipes and joints, custom components and repair systems can also be tested under realistic operating conditions.

These include, for example, fittings and adaptors, bespoke components made from GRP or plastic, valve connections, flange and coupling systems, prototypes and new developments, repair systems such as liner end sleeves, and other components that are subjected to recurring pressure and load cycles during operation

Test parameters such as pressure level, number of load cycles, temperature or test medium can be adapted to the subsequent operating conditions. This makes it possible to verify whether even bespoke designs and special solutions can withstand the expected stresses over the long term.

Particularly for new developments, repair systems and project-specific custom solutions, the DLT offers the opportunity to verify performance under realistic operational loads and to identify potential weak points at an early stage. This enables robust evidence to be provided for customers, operators and approval procedures.

The dynamic load test simulates the stresses to which pressure pipe systems are actually subjected during subsequent operation. These include, in particular, recurring pressure surges, pressure fluctuations and cyclic loading, such as those caused, for example, by the switching on and off of pumps, the opening and closing of valves, or changes in flow rate.

During the test, the entire system is subjected to cyclic loading under realistic conditions. This makes it possible to assess how well pipes, pipe liners, joints, flanges and other system components withstand these stresses over the long term.

The DLT thus replicates typical operating conditions in pressure pipelines and enables a practical assessment of the long-term durability of the entire system.

The pressure pipe cyclic loading test can be carried out using various test media in order to simulate the future operating conditions as realistically as possible. Drinking water is frequently used as the test medium. However, depending on the specific application, other liquids may also be used. This allows the behaviour of the pipe system under actual operating conditions to be reliably assessed.

The dynamic load test can be used to test pressure pipe systems with various nominal diameters. The maximum nominal diameter that can be tested depends on the specific test specimen and the requirements of the test.

Currently, the DLT can be used to test pressure pipe systems and components up to a nominal diameter of DN 500. These include, for example, pressure pipe liner systems, GRP pressure pipes, flanged joints, fittings and connection systems.

Furthermore, customised test set-ups for other dimensions or specialised system solutions can also be provided on request.

The dynamic load test provides comprehensive information on how a pipe system behaves under realistic cyclic pressure loads. The test demonstrates whether the system can withstand the loads encountered during operation over the long term and can be used safely.

Typical test results include verification of the tested system’s resistance to pressure cycling, the number of load cycles successfully completed until the end of the test or until failure occurs, insights into long-term behaviour under recurring pressure loads, documentation of any damage or weak points – for example, on pipe walls, joints, flanges or connections – and an assessment of the system’s integrity during and after the test.

A particularly valuable aspect of the DLT is that it allows not only individual components but the entire pipework system to be tested under load. This enables the identification of potential weak points at joints, transitions or connections, which often remain undetected during tests focusing solely on materials or components.

The results provide manufacturers, network operators and designers with a sound basis for demonstrating a system’s suitability for its intended use and for assessing its long-term operational safety.

The dynamic load test is suitable not only as a verification and type-approval test, but also for product development.

Particularly during the development phase, manufacturers can assess how changes to materials, wall structures, joints or manufacturing processes affect performance under realistic operating conditions. Cyclic loading often enables weak points to be identified before a product is launched onto the market.

Typical applications in development include comparisons of different material formulations, optimisation of pipe liners, pipes and connection systems, evaluation of new resin systems or reinforcing materials, investigations into flange, socket or coupling connections, determination of safety margins against pressure surges and cyclic loading, and identification of failure mechanisms at an early stage of development

Development projects do not necessarily have to undergo the same test programmes as those required for qualification or approval testing. Depending on the specific requirements, shortened test cycles can be employed, and test parameters such as pressure level, number of load cycles or load sequence can be specifically adapted to the respective development objectives. This enables new products and system solutions to be efficiently evaluated and optimised.

The particular advantage of the pressure pipe cyclic loading test is that it does not merely examine individual material samples, but tests the entire system under realistic loading conditions. This makes it possible to identify interactions between the pipe, the liner, the jointing technology and the fasteners, which are often overlooked in conventional material tests.

Styrene is an important raw material and processing aid in the plastics industry. It is used in the production of various plastics that are incorporated into a wide range of construction products. Styrene and styrene-based compounds can be used to manufacture thermoplastics, thermosets, and elastomers.

In the field of thermoplastics, styrene is the basic building block of polystyrene. Polystyrene is used to produce insulation materials such as EPS (expanded polystyrene, often known as Styrofoam®) and XPS (extruded polystyrene), which are widely applied for thermal insulation in both building and civil engineering projects.

In thermoset applications, styrene is commonly used as a reactive diluent in unsaturated polyester resins. During the curing process, the styrene reacts chemically with the resin and becomes part of the final polymer structure. This makes it possible to manufacture thermoset materials and composite products such as fibre-reinforced components and CIPP liners used for trenchless sewer rehabilitation.

Styrene-based compounds are also used in the production of elastomers. Examples include certain styrene-butadiene rubbers (SBR), which are commonly found in seals, gaskets, and other flexible engineering components.

In addition, styrene may be present in coating and paint systems that are formulated with styrene-containing resin technologies.

The role of styrene therefore depends on the specific product and application. It may serve as a raw material for thermoplastic plastics, as a reactive diluent and crosslinking component in thermoset resin systems, or as a constituent of elastomeric materials. As a result, styrene contributes to the manufacture of a wide variety of construction products with different performance characteristics.

No, not every pipe liner contains styrene. Whether styrene is used depends on the resin system selected for the application. CIPP liners based on polyester resins or vinyl ester resins typically contain styrene as a reactive component of the resin.

Styrene-free pipe liner systems are also available, including those based on styrene-free unsaturated polyester (UP) and vinyl ester (VE) resins, epoxy resins, or silicate resins. These systems are often used to reduce odor generation and styrene emissions during installation and curing.

However, “styrene-free” does not automatically mean “harmless.” Styrene-free resin systems likewise contain chemical substances that must be evaluated with regard to occupational health and safety, emissions, and environmental compatibility.

For this reason, both styrene-containing and styrene-free resin systems are used in practice, with the choice depending on their specific material properties and the requirements of the intended application.

In many pipe liner systems, styrene is used as a reactive diluent in unsaturated polyester and vinyl ester resins. It helps maintain the workability of the resin and provides the viscosity required for impregnation and installation.

During the curing process, styrene reacts chemically with the resin. Rather than simply being trapped within the material, it becomes integrated into the developing polymer network and is converted into a solid thermoset plastic.

At the same time, styrene is regarded as a substance of concern because it possesses hazardous health properties and, due to its chemical structure, is related to benzene. For this reason, the residual styrene content of pipe liners is often evaluated. An elevated residual styrene content may indicate incomplete curing or the presence of remaining volatile constituents within the material.

It should also be noted that not all pipe liners are manufactured with styrene-containing resins. Depending on the resin system used, alternative reactive diluents or completely styrene-free formulations may be employed.

Styrene is a reactive diluent commonly used in the production of pipe liners and composite laminates, such as those used in the marine industry. During the curing process, it reacts with other components of the resin system and, ideally, becomes fully incorporated into the polymer structure.

However, if the styrene is not adequately converted during curing, this may indicate that the curing process has not been completed successfully. In such cases, the quality and long-term performance of the finished product may be affected. Potential consequences include reduced mechanical properties, such as strength, stiffness, or load-bearing capacity.

Because styrene is classified as a hazardous substance, its residual content in the finished product is subject to particular scrutiny. This is especially relevant when incomplete curing leaves residual styrene that may subsequently be released from the material.

Determining the residual styrene content provides valuable information about the degree of cure achieved within the material. It helps assess whether the required product properties have been achieved and whether the component meets the applicable quality, performance, and environmental requirements.

Styrene has a characteristic odor and can be detected by the human nose at very low concentrations. Therefore, the presence of a noticeable styrene odor does not automatically indicate a concentration that poses a health risk.

However, because pipe liners are typically enclosed by both an inner and an outer foil layer during installation and curing, strong styrene odors should generally not occur. If noticeable odors are present, the source should be investigated and appropriate precautions should be taken.

Regardless of the concentration, styrene is considered a substance of concern due to its hazardous properties. As a precautionary measure, unnecessary exposure to styrene odors or emission sources should be avoided whenever possible.

Styrene is one of the chemical substances that has been extensively studied for decades. Research has focused particularly on potential health effects in workers who were exposed to styrene over prolonged periods in occupational settings.

What is less widely known is that styrene is not only produced industrially but also occurs naturally in the environment. It has been detected in a variety of foods, including strawberries, cinnamon, coffee, nuts, as well as products such as cheese, beer, and wine. Styrene is also present in tobacco smoke. However, the concentrations found in these sources are generally very low.

Strict occupational safety requirements apply when handling styrene. In Germany, the current occupational exposure limit (AGW – Occupational Exposure Limit) is 20 ppm or 86 mg/m³ as an 8-hour time-weighted average. This limit is intended to ensure that, based on current scientific knowledge, adverse health effects are not expected under normal workplace conditions.

Despite decades of industrial use and extensive scientific investigation, there are no generally recognized occupational diseases that can be clearly attributed to typical workplace exposure to styrene. Nevertheless, potential health effects continue to be studied, and applicable safety regulations are regularly reviewed and updated as scientific knowledge evolves.

As a result, styrene is now considered one of the most thoroughly studied raw materials used in the plastics industry. Its use is subject to well-defined legal requirements and comprehensive occupational health and safety measures.

Styrene, or the styrene monomer, is an important component of many synthetic resins used, for example, in pipe liners or glass-fibre-reinforced plastics. During curing, the styrene reacts with other resin components, resulting in a new plastic material.

Residual styrene, or styrene monomer, refers to the proportion of styrene that has not reacted after curing and is still present in the material. The lower the residual styrene content, the more complete the curing of the resin has been.

Determining the residual styrene content is therefore an important quality indicator. It provides evidence as to whether the curing process has proceeded correctly and the desired material properties have been achieved.

Residual styrene is detected using gas chromatography. This analytical method allows even very small quantities of styrene in the material to be reliably determined. This enables the quality of the cured plastic to be verified.

The residual styrene content is regarded as a measure of the degree of curing of a pipe liner. According to the recommendations of the AVK (German Reinforced Plastics Industry Association), a content of no more than 2 per cent by mass, relative to the resin, is generally considered acceptable.

The 2 per cent rule serves primarily as a quality assurance measure. A low residual styrene content indicates that the chemical reaction has largely been completed and that a durable material has been formed from the resin and styrene.

Conversely, an elevated residual styrene content can affect the material’s mechanical properties, its water absorption and its chemical resistance, thereby compromising the durability of the pipe liner.

Important to note: The 2 per cent limit was not established as an environmental or health limit. It serves primarily as evidence of the material having cured properly.

The residual styrene content is usually determined using gas chromatography (GC). To do this, a small sample of the cured pipe liner is taken and analysed in the laboratory.

During the analysis, the unreacted styrene still present in the liner is extracted from the sample and then quantified by gas chromatography. This allows the exact amount of residual styrene remaining in the material after curing to be determined.

The measured residual styrene content provides an indication of how completely the curing reaction has taken place. A low value suggests that the cross-linking of the resin system is largely complete.

An elevated residual styrene content indicates that the curing process has not been fully completed from a technical perspective and may impair the creep behaviour of the hose liner. The extent of this effect depends on which areas of the laminate are affected.

In the case of UV-cured glass-fibre pipe liners, the load-bearing layers may already be sufficiently cured, whilst elevated residual styrene levels may still be present, particularly in the outer layers. The pipe liner may therefore still meet the required mechanical properties despite the elevated value. Whether its creep behaviour is impaired must be assessed on the basis of the mechanical test results.

If a residual styrene content of more than 2 per cent is detected in a pipe liner, this may indicate that the curing process has not been fully completed. It is then possible that even larger quantities of unreacted styrene are still present in the material.

Possible causes include, for example, insufficient curing, an insufficiently long curing time, or deviations during manufacture or installation. Elevated measured values should therefore be investigated more closely and assessed in the context of the installation conditions and other test results.

In practice, the 2 per cent figure serves as a guideline for assessing curing. If this is exceeded, additional tests are advisable. However, an elevated residual styrene content alone does not provide a reliable indication of the liner’s serviceability or service life.

Particularly in the case of light-curing pipe liners, elevated residual styrene levels may occur primarily in the outer layers of the material, whilst the load-bearing structure inside is already sufficiently cured. Elevated residual styrene levels should therefore always be assessed on a case-by-case basis, taking into account other test results.

In principle, post-curing can help to further reduce the residual styrene content, as any remaining styrene monomers and other reactants that have not yet fully reacted are further incorporated into the polymer structure. In practice, however, post-curing of UV-cured pipe liners that have already been installed often presents significant technical and economic challenges.

The majority of the curing reaction has already taken place at the time of installation. The remaining post-reaction proceeds much more slowly and releases only a comparatively small amount of reaction heat. As a result, post-curing often gets off to a slow start and requires additional energy input. At the same time, heat is dissipated via the surrounding existing pipe, which can further slow down the reaction.

Furthermore, in the case of pipe liners that have already been installed, the side inlets are often open and the sewer has been returned to service. The effort involved in cleaning, preparing and carrying out subsequent UV curing is therefore usually considerable.

For these reasons, post-curing to reduce the residual styrene content is generally not economically viable. Whether it is technically feasible or likely to be successful in individual cases must be assessed on the basis of the specific conditions.

Styrene is classified as a substance hazardous to water bodies in the GESTIS substance database. If liquid styrene enters water bodies or the soil in significant quantities, it can harm aquatic organisms and should therefore not be allowed to enter the environment uncontrolled. Furthermore, although styrene is biodegradable, it must be treated as an environmentally hazardous substance due to its properties.

However, the situation is different for cured pipe liners: during the curing process, the vast majority of the styrene reacts chemically to form a solid plastic composite. After curing, only small amounts of so-called residual styrene generally remain in the liner. Whether and to what extent styrene can be released from this depends, amongst other things, on the resin system, the quality of the curing process and the operating conditions.

For this reason, residual styrene levels and, where applicable, other emissions are tested in practice. In the case of pipe liners that have been manufactured to the correct standards and have cured sufficiently, it is not expected that significant quantities of styrene will be released into the environment. However, during processing and curing, appropriate protective measures must be taken to prevent emissions into the air, soil and water.

In this context: styrene itself is a substance hazardous to water. In a properly cured pipe liner, however, it is predominantly chemically bound, meaning that the finished product does not normally pose a significant environmental risk due to styrene.

Styrene has been used in polyester and vinyl ester resins for decades because it fulfils several important functions simultaneously. As a reactive solvent, it reduces the viscosity of the resin, thereby enabling the hose liner to be impregnated evenly and completely. During curing, styrene reacts chemically with the resin and becomes part of the resulting plastic.

This produces fibre-reinforced composites with good mechanical properties and long-term durability. These properties are particularly important in the rehabilitation of public sewer networks, where high mechanical strength and a long service life are required.

Styrene-free resin systems based on acrylates or methacrylates are also used as an alternative today. These are employed in particular where odour emissions need to be kept to a minimum, for example in house service line liners or during renovation work in sensitive environments. However, these resin systems differ both in their processing behaviour and in the properties of the cured material. For example, they may result in more brittle materials or impose different requirements on curing and application.

It is also important to note that styrene-free systems are not automatically free from properties that may pose a risk to health or the environment. The acrylates and methacrylates used are also chemical substances with their own hazard characteristics and corresponding occupational health and safety requirements.

No universal substitute for styrene has therefore yet become established. The choice of resin system always involves balancing workability, material properties, emission behaviour, occupational health and safety, and cost-effectiveness. For this reason, both styrene-containing and styrene-free resin systems are used in sewer rehabilitation, depending on the specific application. In particular, for in-situ rehabilitation in the public sewer network, styrene-containing polyester and vinyl ester resins continue to be used predominantly due to their proven workability and favourable material properties.

Both styrene and methacrylates are chemical starting materials which, once cured, are largely bound within the plastic matrix. For the purposes of environmental assessment, therefore, the main factors of relevance are potential releases during processing or from unreacted residual quantities.

Styrene is generally classified as posing a greater risk to water bodies than many of the commonly used methacrylates. However, some methacrylates may also possess properties that are harmful to the environment. It is therefore not possible to make a blanket assessment of all methacrylates.

In practice, the following applies: provided the material is processed professionally and disposed of correctly, neither styrene nor methacrylates should enter water bodies or the soil. The actual environmental impact depends not only on the substance used but, above all, on the quantity released.

Once a construction project has been completed, the quality of the installed pipe liner is assessed on the basis of a sample taken. To ensure that the test results are traceable and reliable, the sampling process should be supervised by an independent body.

The actual taking of the sample is carried out by the contractor. However, the selection of the sampling point and the sampling process itself are supervised and documented by an independent party, such as a testing laboratory, network operator or engineering firm. This ensures that the sample is taken from a representative section of the installed liner.

If the sampling is supervised by a testing laboratory, this offers the additional advantage that the sample is taken, labelled and prepared for subsequent testing in a professional manner. This ensures that the test results are meaningful and verifiable.

The size of the sample required depends on the planned test. For residual styrene analysis or thermal analysis (DSC), a comparatively small sample is usually sufficient. For mechanical tests, however, such as three-point bending tests, peak compression tests or tensile tests, larger samples are required:

Three-point bending: specimen length: 20 times the wall thickness, specimen width: 350 mm in the axial direction
Residual styrene: 10 × 10 cm (if submitted solely for this analysis)
DMA: length greater than 35 mm, thickness max. 5 mm
DSC: 50 mm × 50 mm or ∅ 50 mm
Tensile test: min. 300 mm in the longitudinal direction, 250 mm in the circumferential direction
Water tightness: 3 test areas with a diameter of 50 mm, sample area: min. 20 × 20 cm (may also be carried out on the test material used for the three-point bending test)

If several tests are planned, we recommend providing the largest possible samples.

UV-curing test specimens must be packed in light-proof packaging.

For each sample, we require a sample accompanying note or a cover letter containing the order details. To ensure that your sample can be clearly linked to your construction project, the following information should be provided:

Client
Contact person for enquiries
Project or works description
Section number or location of the rehabilitation section
Liner diameter and statically required wall thickness (if known)
Product used
Requested tests
Date of installation or sample collection

The sample should be packed in a clean, dry manner and protected from damage and exposure to light. Light-curing pipe liners must be packed in light-proof packaging immediately after sampling (care must be taken to ensure that the samples are not packed in direct sunlight) to prevent any changes to the material properties during storage and dispatch. Suitable materials include, for example, black plastic film or aluminium foil.

Samples sent in should be clearly labelled so that they can later be matched to the sample consignment note containing all relevant order details.

Samples are usually sent via a parcel delivery service to the following address:

Siebert + Knipschild GmbH
Bergstücken 25
22113 Oststeinbek

Alternatively, samples can be delivered directly to the above address. Depending on the project, separate arrangements may also be made for sampling to be carried out by Siebert + Knipschild staff or via a collection service commissioned by us.

In many cases, yes.

Whether several tests can be carried out on a single specimen depends primarily on the specimen size, the wall thickness and the required tests. Some tests require only very small quantities of material, whilst others require larger test specimens.

Through efficient test planning, different tests can be carried out on the same specimen material. For example, after a three-point bending test, residual styrene analyses and calcination/glass content determination can be carried out on the test specimens.

Nevertheless, it is advisable to send in as much sample material as possible to ensure that all the tests requested can be carried out.

If you have any questions about whether your sample material is sufficient, please do not hesitate to contact us.

Once your sample has been received, it is first clearly recorded and prepared for testing. We then carry out the agreed tests in accordance with the relevant standards and test specifications. Depending on the test programme, this may involve examining, for example, mechanical properties, wall thicknesses or material characteristics.

Once the tests have been completed, our experts analyse the results and document them in a test report. This provides you with a basis for assessing the quality and conformity of your pipe liner or the tested product. Please do not hesitate to contact us if you have any questions regarding the results.

We retain test samples for at least three months after the test has been completed. This ensures that we can refer back to the original samples in the event of queries, re-tests or the need to clarify test results. Samples may be retained for longer by individual arrangement.

Plastic waterproofing membranes are flat waterproofing materials made of plastic, which are used to protect soil, groundwater and water bodies. They prevent liquids or pollutants from entering the subsoil or leaking from structures.

They are used in various waterproofing systems, for example at landfill sites, in retention basins, spill containment trays, storage and handling areas for water-polluting substances, and in other environmental and water protection facilities. Depending on the application, the waterproofing membranes are combined with other components such as geotextiles, drainage layers or concrete protection slabs.

To ensure that a waterproofing system can fulfil its protective function in the long term, both the materials used and the welded seams and joints must be installed professionally and inspected regularly.

Plastic waterproofing membranes fulfil an important protective function: they prevent water-polluting substances or contaminated liquids from entering the soil and groundwater. For this reason, laws, regulations and technical standards stipulate that their suitability, quality and correct installation must be verified.

Tests help to identify material faults, damage or installation defects at an early stage, before the system is commissioned. If such defects are only noticed years later, they can lead to leaks, environmental damage and costly remediation work. Identifying and rectifying damage retrospectively is often significantly more costly and time-consuming than carrying out a quality test at an early stage.

Testing ensures that the waterproofing membrane meets the required protection and safety standards and that the facility can be operated reliably in the long term.

The joints between the individual waterproofing membranes are inspected using specialised testing procedures. These tests check whether the welded seam is secure, uniform and permanently watertight.
The tests are carried out both directly on site and on samples taken for laboratory analysis. On site, for example, the seam tightness is checked using compressed air, vacuum or high-voltage tests, whilst the seam geometry is assessed using a ball-head probe, calliper or ultrasonic testing. For pipework systems, the pressure test can also be monitored and documented.
In the laboratory, the material and joint properties of plastic waterproofing membranes are examined. This includes, amongst other things, tensile tests on plastic waterproofing membranes and geotextiles, the determination of area mass, thickness and density, the measurement of the melt flow rate (MFR), and the testing of dimensional changes following heat storage. To assess the welded seams, peel tests and tensile shear tests are carried out in particular. In addition, technical bending tests can provide insight into the behaviour of the materials under load.

Tests on plastic waterproofing membranes are not only used to detect damage and installation defects. They also show whether the material meets the specified properties and requirements.

In the field of defect and damage detection, for example: defects in welded seams, inadequate bonds between individual membranes, leaks and limitations in mechanical load-bearing capacity be detected.

Specialised examinations of welded seams or load plate compression tests enable an assessment of whether the waterproofing system is suitable for the intended operating and load conditions, or whether there are indications of limited serviceability.​‌

On site, the main focus is on checking that the installed plastic waterproofing membranes have been fitted correctly and are watertight. In addition to inspecting the quality of the workmanship, this includes, for example, leak-tightness tests on welded seams and checks on seam geometry.

In the laboratory, the properties of the materials and welded joints are examined in more detail. This includes, amongst other things, tensile tests, peel tests and shear tests, as well as the determination of various material parameters. By combining on-site and laboratory tests, the quality of a waterproofing system can be reliably assessed.