The first plastic material which was used for sewer and drainage systems was PVC (polyvinyl chloride) because of its ease of installation and competitive cost. While PP (polypropylene) has always been used for special applications (high temperatures and industrial field), HDPE (high density polyethylene), in its extruded solid wall version, has been used only occasionally as it is too expensive.
In the ‘80s, the first HDPE pipes for sewers up to 3.6 m in diameter were successfully used as they combined a very good resistance to aggressive wastewater with other important characteristics such as lightness, high ring stiffness and competitive costs. This is how Bauku, Henze, KWH sewer drainage pipes were manufactured and patented and are still available in their latest versions.
With the new licences, the different types of walls were later developed which lead to the manufacture of the black ECOPAL pipe for waste water.
All pipes from reliable manufacturers and installed with the utmost care can give good technical results. Without going into details on the use of all various materials, we will emphasise those concepts which all designers and users should take into account when dealing with sewer systems.
The main requirements for sewer pipes include:
- good hydraulic characteristics on a short and long term;
- suitable resistance to internal pressure even in the case of temporary overpressure;
- good resistance to loads as it is an outdoor corrugated pipe that must be buried;
- excellent bidirectional watertightness of joints on a short and long term;
- excellent resistance to chemical and electrochemical aggressions;
- resistance to abrasion;
- reduced adherence to deposits;
- easy cleaning with modern techniques;
- easy and quick assembly and laying;
- competitive price.
To be more precise about the characteristics described above:
- the compliance of each material with the project requisites must be checked on the basis of realistic and homogeneous elements, especially as regards the hydraulic characteristics (inside diameter and absolute roughness value);
- resistance to chemical, electrochemical aggressions and abrasion must be checked according to waste waters;
- resistance to internal pressure and perfect watertightness even on a long term, apply to all pipes but above all those pipes with spigot joints whose key element is the bell length and the seal characteristics;
- watertightness must be bidirectional: most problems in the existing sewer systems that also affect the treatment plants are caused by groundwater or leaks from the joints;
- high pressure or mechanical cleaning systems may damage some materials causing misalignment of certain types of joints or even failure of the internal pipe wall.
- as regards costs, it should be pointed out that instead of comparing the pipe cost, the comprehensive cost of the whole sewer system must be taken into consideration, including laying costs and all maintenance costs connected with the life cycle of the pipe.
Pipes for sewerage New sewerage pipes