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Pipes made of glass fibre reinforced plastics (GRP) have been produced since the start of the 1960s. Originally, they were used for the discharge of aggressive effluents in industrial undertakings but then became increasingly important in the sewage sector where they are laid today
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(Table: Characteristic values for HOBAS GRP pipes) |
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(Image: Cast iron pipe) Cast iron piping has been used for more than 500 years, originally as grey cast iron piping. They were primarily used for the conveyance of drinking and process water [Biere85]. With the start of gas supplies more than 100 years ago, cast iron piping was used for this purpose as well. Because of their excellent sound absorption characteristics, grey cast iron pipes without sleeves in the sewage sector are primarily used as drain … |
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Unprotected and earth-covered piping of ductile cast iron can be damaged by corrosion from the outside as well as the inside when they come into contact with oxygen-enriched, watery media. Hence, such pipes must be provided with an outer and inner corrosion protection when used in the water or sewage sectors. (Image: Hole corrosion - pitting) |
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(Image: Cast pipe with external corrosion protection in the form of cement mortar coating) Protective internal linings and external coatings are often applied to ductile cast iron pipes to prevent corrosion Coatings of zinc or a zinc-aluminium alloy with a top coat of epoxy resin are standard for the outside corrosion protection of the pipes [EN545:2011], [EN598:2009]. The following coatings are offered for ductile cast iron pipes that are laid into … |
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(Image: Cast pipe with internal corrosion protection in the form of cement mortar lining) The internal corrosion protection must be in the form of a cement mortar coating [DIN2880:1999], [EN545:2011]. According to DIN 2880 and DIN EN 598, aluminate cement is specified as standard in the field of sewerage in order to provide a greater resistance to sulphates. Usually, the layers are 4 mm thick for DN 80 to DN 300, 5 mm for DN 350 to DN 600, 6 mm for … |
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The field of application for ductile cast iron pipes is specified in DIN EN 598, which is the decisive standard for sewers. According to that standard they are not only permitted for gravity piping covered with earth but also for pressure pipes in the range DN 80 to DN 2000. [EN598:2009] According to DIN EN 598, sewage pipes made of ductile cast iron are produced in the nominal sizes DN 80 to 2000 with lengths of 6,000 mm (for DN ≥ 700 also 7,000 … |
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(Image: Attention!) Pipe joints must be leak tight against internal and external water pressure. Movable (flexible) pipe joints (must also be leak tight at the maximum permissible deflection. All parts of the pipeline including the pipe joints and sealings must be designed, produced and examined according to the objective to guarantee the tightness during the construction works (construction state) and the whole planned service life (operation state) … |
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Demands on the pipe joints of jacking pipes (Image: Icon: Watertightness) Tightness against internal and external pressure (Image: Transfer of the longitudinal force) Transfer of the longitudinal force by securing the lateral stability (Image: Corrosion protection end faces of the pipe) Corrosion protection of the end faces of the pipe |
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In the following, both historical and current pipe joints in sewage systems are presented. In general these pipe joints were divided into the following
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(Image: Plug joint) Plug joint A plug joint (in practice also called a socket-and-spigot -joint) is a flexible pipe joint. Spigot and sockets involve a normal pipe end, the spigot, being inserted into the socket or bell of another pipe or fitting with a seal being made between the two within the socket. (Image: Clamp joint) Clamp joint A clamp joint is a flexible pipe joint whose sealing effect is achieved by clamping a sleeve over the pipe ends to be … |
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(Image: Stuffing box joint) Stuffing box joint A stuffing box joint is a flexible pipe joint whose sealing effect is achieved by plugging together the spigot end and the socket and then pressing in an elastic sealing medium by means of a follower nut. (Image: Adhesive joint) Adhesive joint An adhesive joint is a pipe joint whose sealing effect is achieved by gluing together the pipe ends that are to be connected. Depending on the type of the applied adhesive … |
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(Image: Welding bead) Welded joint A welded joint is a rigid pipe joint whose sealing effect is achieved by welding the pipe ends together. (Image: Flanged joint) Flanged joint A flanged joint is a rigid pipe joint whose sealing effect is achieved by placing a sealing medium between the flanges. (Image: Pipe joint with elastic sealing medium) Elastic sealers Elastic sealers are sealers composed of elastomers (see DIN 7724 [ [DIN7724:1993]]), that are inserted … |
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For a long time, the pipe joint represented the weakest element of drains and sewers. This holds also true for the joints of concrete- and reinforced concrete pipes from the beginning of the sewerage technology. The first concrete pipes did not have integrated socket ends. Their butt ends were pushed hard up against each other during laying and the ends were covered with a 5 cm thick cement mortar into which a wire mesh was placed. This model can … |
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The tongue and groove joint consists of a tongue and groove fabricated on matching pipe ends to provide some indexing when the two pipe ends were assembled. This joint was the most common in use for concrete pipes. DIN 1201 supplementary sheet, February 1923 “Sewerage pipes of concrete” specifies that “a better joint has not been found to this day”. The approach to standardise this joint seemed unacceptable in the past. It was only demanded that … |
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From 1951, plastic, cold-working sealing materials in the form of strips for tongue and groove joints as well as putties and trowelling masses were applied to pipes with tongue and groove joint and also with sockets. With both sealing media, the free gap between the pipes had to be completely filled. This process then replaced the usual caulking method for gravity sewers and pressure pipes [BDB78], [ATV82]. (Image: Plastic gasket band in lip-ended … |
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(Image: Elastomer ring seal) Elastomer ring seals were not used in the sewage sector until the 1960s. Since that time, they have prevailed as sealings for spigot-and-socket joints (bell socket or lip) for pipes made of concrete, reinforced concrete, steel fibre concrete as well as other material. (Image: Attention!) An elastomer is a polymer with viscoelasticity (having both viscosity and elasticity) and very weak inter-molecular forces, generally having … |
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The most widespread type of elastomer ring seals was the O-ring seal. The elastomer ring is stretched onto the spigot end of the pipe under preliminary strain and rolls into its final position while it is simultaneously deformed when it is pushed over the spigot end or the collar of the adjoining pipe. (Video: Rolling ring seal) Animation: Rolling ring seal [Image: S&P GmbH]. This interactive object is only accessable in the online version of the module. |
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In order to achieve leak tightness an O-ring must be compressed. This is called the initial compression (velvet arrows) and results in the initial sealing force. The leak tightness of the O-ring increases when under system pressure (red arrows) which leads to the total compression force. (Image: Method of operation of an elastomer sealing ring with reference to [BDB78] [Kitte75] [Image: S&P GmbH]) |
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(Image: Attention!) Attention: According to the quality assurance guidelines in Germany, O-ring seals are no longer permitted because of their sensitivity to errors during laying. Since 1994, pipes made of concrete or reinforced concrete are exclusively produced with sealants of elastomers with a dense structure and a solid sealing cross section. Only slide ring seals are allowed that are either rigidly integrated in the socket at the factory or put … |
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For slide ring seals, the sealing ring is stretched into its final position in a groove or is placed over the spigot end in front of the collar (also called support edge. In pushing the pipes together, the sealing ring is compressed without changing its position and thus achieves its sealing function [BDB78]. A butt joint between the pipes of 10 mm to maximally 20 mm (minimum dimension 5 mm according to DWA-A 139) permits corresponding movements of … |
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For concrete pipes > DN 1200 slide ring seals that are rigidly included in the socket at the factory (Image left), slide ring seals that are put onto the spigot end at the factory in front of a collar (Image centre) and slide ring seals that are put onto the spigot end in a groove (Image right) can be used. For slide ring seals on the spigot end in front of a collar (Image centre) the ring has to have a wedge-shaped cross section [FBS2011]. (Image: … |
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The lip seal counts among the seals that are rigidly integrated into the socket end at the factory, as it is cemented into the socket end during pipe manufacture. Before pushing the pipes together at the construction site, the foamed material protective ring is removed and a lubricant is applied to the spigot end. The sealing of the pipe joint is achieved by the lip seal that is pressed against the spigot end when this is pushed into the socket end [… |
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Further examples for integrated sealing elements are the gasket that is pre-lubricated at the factory and the self-lubricating gasket. The first type prevents the use of inappropriate lubricants, while the second type prevents damages at the sealing element because less insertion force is required [FI-Trelleborg2011]. (Image: One-piece pre-lubricated integrated seal for concrete pipe and manhole systems ("Forsheda 166")) |
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