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Nov 03, 2004 |
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In the case of sewers, the wear process takes place in the region of the wetted pipe inner surface and here mainly in the region of the invert. It can be measured by the material removal (fines) and leads to an increase of the roughness of the walling and, in extreme cases, to destruction of the piping (Abschnitt 2.6.1). The usual method of measuring the wear variables is given by the reduction of the wall thickness of the body exposed to the wear (… |
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Nov 03, 2004 During the conveyance of water - solids mixtures as is usual in sewers, wear is caused primarily by various materials carried along by the water, such as sand, gravel, solid metal parts, textiles, etc. In the present application this is dependent on [Järve93] :
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Nov 03, 2004 In sewage channels, stresses can arise during operation, which result in drip erosion in the region of the building connections due to the impact of incoming sewage on the sewer wall opposite the connection and in drop installations. Damage due to this type of stressing is not yet known. |
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Nov 03, 2004 When a flow of water at a high velocity is parallel to a border surface, then every geometric change in this surface has a resultant on the flow and causes local regions of lower pressure. When the static reduced pressure of the flowing water then falls below the vapour pressure, water vapour bubbles are formed. If these occur in regions in which the static pressure again lies above the vapour pressure - this is mostly shortly behind the position … |
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Nov 03, 2004 Fluid erosion, in which material removal is caused by the action of flowing liquids (water) in sewers, is only of secondary importance when compared to wear caused by materials carried along with the sewage (flushing wear (Abschnitt 2.5.2.1)). |
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The stress on the surface of a solid body due to contact and to relative movement with a solid, fluid or gaseous counter body is designated as the tribological stress. "Tribology" according to DIN 50323 [DIN50323-2:1995], is the science and technology of surfaces acting on one another in relative movement. An overview of the tribological stresses during operation of the sewer piping is given in Tabelle 2.5.2. Added to this are stresses from the cleaning … |
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As already mentioned, mechanical wear causes the removal of the piping material from the inner wall surface. The consequences of the damage [ATVM143-1:1989] are:
A further danger is in the damage of corrosion protection that may possibly exist (… |
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Nov 03, 2004 According to [DIN50320], wear is the continuing loss of material from the surface of a solid body due to mechanical action, i.e. contact and relative movement of a solid, fluid or gaseous counter body. In general usage, the term "wear" is used for the process of attrition as also for its consequences. In order to distinguish them, according to [DIN50320], there can be used for the process the term "wear process" and for the consequences the terms "… |
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Nov 03, 2004 (Image: Hole corrosion - pitting) Corrosion without mechanical stressing, e.g.
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Nov 03, 2004 Corrosion with additional mechanical stressing, e.g.
Because the causes and sequence of corrosion for metallic … |
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According to DIN 50900 Part 1 [DIN50900], corrosion is understood as the reaction of a material with its environment, which causes a measurable change in the material (corrosion manifestation) and which can lead to the impairment of the function of a component or a complete system (corrosion damage). Especially for sewage installations, [ATVM168] defines corrosion as follows: "Under corrosion in the field of sewage installations there are understood … |
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This type of corrosion can occur due to the mutual influence (material incompatibility) between:
Here, it is limited to pipe jointing regions or transfers to other pipes or structures. A structural change of the pipe material or sealing material occurs here resulting in leaks or a reduction of the bearing strength. In order to … |
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All natural soil originated due to chemical and physical weathering of the rocks. The reactive medium "soil" consists in its components in accordance with the four weathering products: sand, clay, lime and humus.
From a chemical point of … |
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Nov 03, 2004 According to [ATVM143-1:1989], the cause of external corrosion of sewers of cement-bound materials can be due to the following:
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Internal corrosion is caused by aggressive substances already in the sewage or which form during the flow by means of chemical processes. Corresponding concentrations of the substances and low pH values (Tabelle 2.6.3.2.1) low flow velocities, long flow periods, high temperatures, bacterial influences and other parameters can increase the aggressiveness strongly (Bild 2.6.3.2.1) (Bild 2.6.3.2.1) (Bild 2.6.3.2.1). (Table: Limiting values for evaluating … |
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A particular type of internal corrosion presented by partially filled sewers of cement-bound materials is the biogenic sulphuric acid corrosion (BSC) also called sulphide corrosion or biogenic acid corrosion. Whilst only the wetted sewer region is affected by the corrosion … |
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In order to estimate the rate of corrosion in cement-bound pipes as a result of biogenic sulphuric acid corrosion, there are in existence various values based on experience and models, which partly however, provide very different results [Lohse95] :
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Nov 03, 2004 According to [ATVM143-1:1989], internal corrosion can have the following causes:
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With cement-bound building and other materials, one differentiates [ATVM143-1:1989] between:
Both manifestations of corrosion can occur either in locally limited areas, or can be spread over parts of a section or whole sections of a sewer and can also be distributed unevenly over the cross section (Bild 2.6.3) (Bild 2.6.3) (Bild 2.6.3).
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The possible consequences of damage resulting from corrosion depend substantially on the type of corrosion, its manifestation and extent and, according to [ATVM143-1:1989] are
Internal corrosion causes an additional increase in the roughness of the wall and causes a reduction … |
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Nov 03, 2004 |
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According to the definition in ATV-A 127E [ATVA127a], taking into account EN 1610 [DINEN1610:1997] and EN 1295 [DINEN1295-1], one distinguishes flexible sewage pipes from rigid pipes as follows: "Rigid pipes are those in which the loading does not produce any appreciable deformation and therefore has no effect on pressure distribution." "Flexible pipes are those whose deformation considerably influences the loading and pressure distribution as the … |
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Deformations in the sense of damage can be caused by [ATVM143-1:1989] :
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The possible consequences of damage of deformation are, according to [ATVM143-1:1989] :
Each deviation from the ideal hydraulic … |
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