Pipe liner

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A pipe liner is a fiber composite material that is used for the trenchless rehabilitation of underground, pressureless drainage networks ( sewer systems ). The process is known as pipe lining . Its main components are thermosetting synthetic resins , which form a matrix through a chemical reaction, as well as textile materials such as glass fibers, which have a reinforcing function, and nonwovens, which serve as pure form carriers for the resin matrix. Targeted admixture of so-called aggregates can increase mechanical strength in certain areas.

Resin types

The most common pipe liner systems are based on unsaturated polyester resins (UP resins) of group 3 according to DIN 18820-1 table 1 or type 1140 according to DIN 16946-2. The distinctive styrene scent serves as an infallible indicator of their use. In second place are the epoxy resins (EP resins) of type 1040-0 according to DIN 16946-2. Furthermore, silicate resins or, for special applications, the vinyl ester resins of type 1310 according to DIN 16946-2 are also used. In principle, all resin systems currently approved by the DIBt in Berlin that are used in pipe lining are of a higher quality than, for example, in yacht building.

According to DIN EN ISO 11296-4 (since 07/2011 replacement for DIN EN 13566-4) section 5.1, a pipe liner consists of a resin matrix and a carrier fiber with the optional use of reinforcing fibers and foils, some of which are reversible (inner foil) and then to be removed for the renovation. Some systems leave the inner foils in place after curing is complete, without them being part of the system. In some systems, mainly based on synthetic fibers, the inner film was included in the DIBt approval as an integral part. For this purpose, the inner film must meet the requirements of a test program set by the DIBt. According to DIN EN ISO 11296-4, pipe liners must have a minimum thickness of 3.0 mm. Thinner systems are not to be called pipe liners.

Pipe liners can be used as a statically supporting pipe in the pipe. To do this, the system must meet the requirements of ATV Leaflet 127-2 and be statically dimensioned. According to DIBt, the material in this case must have a ring stiffness of min. 5,000 N / m². For the static dimensioning, the material must achieve defined, mechanical parameters that are to be determined by the suitability test or in the context of a DIBt approval. DIBt approval is mandatory for use on private land. As part of the DIBt approval, the material must go through a series of suitability tests (test program) in which the specific properties of the starting materials and the resulting composite material are determined and then stipulated. This is done by test centers accredited for this purpose and recognized by the DIBt as a certification body. Furthermore, the manufacturer must define and stipulate the process technology required for the installation and the devices required for it.

Curing

The process technology for curing the pipe liners is currently divided into four main groups:

  1. Inversion or eversion of the pipe liner using water pressure and curing using warm water.
  2. Inversion or eversion of the pipe liner using air pressure and curing using steam.
  3. Pulling in the pipe liner by means of a cable winch, erecting and compacting by means of air pressure and curing by means of UV-sensitive photoinitiators.
  4. Combination of the pull-in and inversion process and hardening using hot water.

In the case of inversion, the pipe liner is brought into the position to be rehabilitated by turning inside out from the inside to the outside with the aid of water or air pressure - similar to turning a sock from left to right. For this purpose, depending on the bottom depth of the section, a tower must be built above the launch shaft in order to adjust the water pressure to the local and system conditions. With the inversion with the help of compressed air, the pipe liner is brought into position via a drum. The liner is completely rolled up in a pressure-tight drum and then inverted using compressed air.

In principle, most of the systems used are able to harden under ambient temperature. However, higher reaction conversions are achieved in the formation of the resin matrix if the reaction of the resins is initiated or promoted by temperature. This can be done by adding energy in the form of heat. Two variants are currently in the foreground, hot water hardening and steam hardening.

Systems based on UV-sensitive photoinitiators are enjoying increasing popularity. These systems start the reaction by using so-called chemical radicals. In this case, radicals are destroyed by initiation as a result of UV radiation and the reaction is enabled. The UV radiation must be precisely matched to the resin system.

In all cases an exothermic reaction is initiated which leads to the hardening of the material. In the case of hot water processes, the surrounding water also acts as a moderator for the reaction, because the heat generated during the reaction is absorbed by the water and prevents uncontrolled overheating. In the UV-initiated reaction, the curing process is controlled by temperature sensors on the lamp train. The temperatures are transmitted to the operator in the control room. This can then correct the speed of the UV lamp train. In the steam curing process, the reaction is regulated by controlling the steam temperature. The temperature sensors required for this are located between the laminate and the old pipe wall of the section. It is important that the sensors are arranged in the sole area. Since condensate also forms during curing by means of steam, which runs off through the sole and has to be removed, the reaction in this part of the laminate can be influenced.

impregnation

The manufacture of the systems differs in terms of factory and local impregnation.

Factory impregnation

When the systems are manufactured in the factory, the hoses are assembled in a factory (diameter, wall thickness and length) according to customer requirements and then soaked in resin and delivered to the construction site. Depending on the system, it must be ensured that the impregnated hose is protected either from heat or from sunlight. Heat-sensitive systems are usually delivered ice-cold, UV systems are usually delivered in a wooden box. All systems approved by DIBt have a specific, defined installation temperature range that must be observed. The DIBt-approved systems can be recognized by a clearly visible Ü mark on the transport box. This Ü mark guarantees compliance with the material components specified by the DIBt. An approval number that always begins with Z-42.3-XXX is on the Ü sign. The XXX stands for a system-related three-digit number. In addition, the DIBt-recognized, independent certification and testing center is part of the Ü mark. Only monitored products meet the requirements of the DIBt and guarantee the customer the use of process-specific material components and compliance with the required quality.

Local impregnation

When the hose is impregnated locally, the impregnation process takes place in a mobile mixing plant. This consists of a conveyor belt, the tanks for the components and a static mixer that must be matched to the resin mixture. It is also advisable if the tanks can be air-conditioned so that the processing temperatures can be maintained. By applying a vacuum, the air is drawn out of the hose and the resin mixture is distributed in the carrier fiber. Since the fiber is sealed by a working film that is laminated on one side, a negative pressure can be built up. In the case of the inversion systems, this film forms the later inside of the new pipe after the renovation has been completed. In general, only synthetic fiber liners are locally soaked at the moment. Fiberglass liners are currently only manufactured at the factory. This also applies to pipe liners; Short liners, which are related in structure, are also made locally with glass fibers. Here, too, there must be a Ü mark on the container or as a package insert with the corresponding approval number. Unmarked products are not subject to monitoring.

In order to ensure sufficient reaction conversion, the curing process must take place under specially defined conditions. This concerns z. B. the warm-up phase in which the material is preheated, the hardening phase in which the matrix is ​​formed and the cooling phase in which stresses in the material are reduced. Uncontrolled curing that deviates from the system-specific parameters generally leads to unsatisfactory results in terms of mechanical strength, which provides information on the degree of curing of the material.

quality control

As part of the renovation of the public sewer network, samples of the plastic specially prepared in the manholes are sent to a laboratory for quality assurance . In general, the short-term mechanical values ​​such as flexural strength and modulus of elasticity are determined by determining the wall thickness in accordance with DIN EN ISO 178 / ISO 11296-4 and compared with the specifications of the DIBt approval or static calculation (suitability test). In addition, the waterproofness of the laminate is determined using a method derived from DIN EN 1610.

The quality of the systems used for the rehabilitation of property drainage pipes can also be largely checked with the help of thermal analysis. The procedure used for this is abbreviated with the letters DSC analysis. For quality assurance, there are test laboratories accredited especially for this area.

The pipe liner is a quality product that is constantly being developed. For a successful renovation it is important that the standards, technical regulations and process engineering of the systems are adhered to by trained personnel, from planning to execution and quality assurance.

literature

  • Pipeline rehabilitation association : rehabilitation of accessible drainage lines and sewers as well as manhole structures . Vulkan-Verlag GmbH, Wiesbaden 2007, ISBN 978-3-8027-5015-1 .

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