Vitrified clay pipes are composed of crushed and blended clay that are formed into pipes, then dried and fired to temperature of almost 1200ºC. This firing gives the pipes a glossy finish. Vitrified clay pipes have been used for centuries and are strong, resistant to chemical attack, internal abrasion, and external chemical attack. They are also heat resistant & non conductive.

Vitrified clay pipes characteristics which become reasons for using clay pipes can be summarized as follows :-

Chemical Resistance
Vitrified clay pipes and fittings to the specification of EN 295 are resistant to chemical attack in a pH-range from 0 - 14. For special circumstances or application, the chemical resistance may be determined by the use of the test in clause 10 of (SASO/GSO/EN295-3: 2008).

Corrosion Resistance
Vitrified clay material is resistant to all types of chemicals over the entire wall thickness. The resistance of the vitrified clay material and seals is tested using chemicals, including sulphuric acid, at pH 0 and NaOH at pH 14, in conformance with EN 295.

The formation of H2S in sewage is a consequence of the natural biological decomposition of sulphur-containing organic and inorganic matter (proteins, sulphates). H2S mainly forms under anaerobic conditions by sulphate reducing bacteria (desulfovibrio desulfuricans) in the slime of a matured sewer and to a lesser extent by bacteriological processes in the sewage. In gravity sewers the formation of H2S commences after the oxygen originally present in the sewage has been consumed by manifold biological processes. This is followed by the anaerobic decomposition with an ever increasing formation of H2S which slowly escapes into the sewer atmosphere. Turbulence in the sewage stream increases the escape of the gaseous H2S. The formation of H2S is supported by long sewage flows, low flow velocities and high sewage temperatures.

The formation of H2S, and the oxidation into H2SO4 by bacteria (e.g.thiobacillus thiooxidans) living on the moist surface of the sewer occurs not only in gravity sewers, but more severely in pressure pipe lines, where, due to the absence of an atmosphere, continuously ideal conditions for the sulphate reducing bacteria prevail. The biologically induced H2S - corrosion has its effects only above the surface level of the sewage stream, where the sulphuric acid reacts with the lime content of cement-bound pipe materials. On concrete pipes which contain limestone as the aggregate the effects of biological H2S -corrosion show later than on those having quartzistic aggregate. In general a progression in corrosion of concrete sewers having a constant presence of hydrogen sulphide in the sewer atmosphere can be expected with 3 - 6 mm/y. Vitrified clay pipes are immune to sulphuric acid.
100 mm diameter cast iron pumping main after being in service for 25 years. The corrosion is due to graphitization. 235mm diameter asbestos cement pipe which was bitumen lined, showing the effects of 14 years of acid attack.

Mechanical Resistance
Vitrified clay pipes have the ability to withstand high static and dynamic loading because they are rigid material and is not subjected to the problems of deflecting or flattening under load. The characteristics of clay pipes remain constant due to its inherent physical properties.
Vitrified Clay Pipe is a rigid material and is not subject to the problems of deflecting or flattening under load. Severely deflected plastic pipe must be replaced at excessive unplanned expenses.

Tight Joint
Vitrified clay pipelines are designed with tight joints for two reasons (to provide water tightness and flexibility to a pipeline). These durable joints lock out the ground water that can increase the volume of sewage inside the pipeline, and also stop the sewage leakage of the pipeline (VCP resist water infiltration and exfiltration).

The pipe joint flexibility allows angular deflection against any movements which may occur during pipeline installation or the ground settlement.

Jetting Resistance (Resistance to high-pressure cleaning)
Vitrified clay pipes can withstand a cleaning test at 120 bar. This makes VCP scores considerably better than many other types of material.

Hydraulic Capacity
Vitrified clay pipes have and hold a smooth inner surface (wall roughness between 0.02 and 0.05 mm). Especially in the case of limited slopes, this offers quite some advantages. Because of the high erosion resistance, vitrified clay can even be used for slopes up to 10 m/sec., without any danger of material deterioration (for concrete, for e.g. the maximum slope is only 3 m/sec.). See also EN 295, chapter 2.16.

Vitrified Clay Pipe
PVC Pipe
Vert. Cast Concrete Pipe

The vitrified life cycle is calculated to 100 years, even in the hardest conditions. Furthermore, vitrified clay is the only material that resists regular rinsing and unclogging by means of high water pressure techniques. This means that vitrified clay pipe canals can be written down over a longer period and that maintenance, renovation and replacement costs can be limited to a much lower level.

High Abrasion Resistance
Vitrified clay has high abrasion resistance, which is equally true for the glaze and the rest of the wall.
Pipe (All 8" Diameter) Wall Thickness Abraded
Inches Percent
1 Vitrified Clay Pipes .003 0.3
2 Solid Wall PVC .027 10.35
3 Solid Wall PVC with filler .043 19.4
4 Profile Wall PVC .048a* 100.0a*
5 PVC Truss .059a* 100.0a*
6 ABS Truss .067a* 100.0a*
a – Complete abrasion through the interior lining.

Environmental friendly (From earth to earth)
The raw materials for manufacturing vitrified clay pipe are clay and recycled materials from the ceramic industry. Mining of the raw materials and subsequent restoration of a natural environment take place in an environmentally friendly manner. In addition, the environmental impact of manufacturing of vitrified clay is relatively small compared with most other types of sewer materials. The long service life of vitrified clay is an additional decisive factor in this regard. No polluting products are generated at the end of the life cycle.

Economic Consideration
The management of domestic and industrial waste water transport, infrastructure and treatment is most often a local government issue. The authority is obliged to pay particular attention to the economic aspects. These include the one- off cost for construction of the sewer line and the operation and maintenance cost (subsequent cost). The cost for construction of a sewer line is determined largely by the location and the type of construction. A line laid through a green field will cost less than a sewer along a major street. In both cases, however, the cost of the pipe material is only a fraction of the entire cost of the project.

The operating and maintenance cost are the basis of the charges levied for use of the sewer. These costs represent a constant expense. The calculation of the anticipated magnitude of these expenses is therefore even more important than that of the construction cost. These running costs include:

• Capital expenditure • Depreciation
• Maintenance • Administration

It can be assumed that the estimated cost for maintenance and administration will be the same for all sewers. With regard to the capital expenditure, (interest and amortization) and the rate of depreciation, a different cost must be anticipated, depending on the pipe material. Features such as resistance to corrosion and chemical attack, abrasion, temperature, as well as their impermeability, sewers constructed from vitrified clay have an above-average life-span. The higher cost for interest on the capital required to the purchase of vitrified clay pipes as the chosen material as opposed to cheaper, less permanent materials is therefore more than compensated.
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New Al – Kharj Highway,
P.O. Box 17952,
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Kingdom Of Saudi Arabia.
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