SELECTION OF PIPE MATERIALS

The following factors should be considered in the selection of pipe materials for sewers:

Technical factors

1. Length of pipes: Individual pipe lengths vary considerably across the range of pipe materials. Leaking pipe joints are common source of infiltration and so minimizing the number of joints may assist in the reduction of infiltration and exfiltration.
2. Sewage quality: Deterioration to the fabric of a correctly designed sewer system should be minimized by application of an appropriate pipe lining or by pre-treatment or prohibition of the aggressive substances entering the system.
3. Ground conditions: The principal chemical attack to the pipes is from sulphates in soils and groundwater. RCC pipe is vulnerable to sulphate attack, but will give satisfactory performance in sulphate bearing soils provided that the sulphate resistant cement is used in the manufacturing of the RCC pipes. Acids, oily and tarry substances may accelerate the corrosion of materials and attack polymeric materials, rubber, jointing seals and protective coatings to concrete and metals.
4.   Durability aspects: Fundamental to the choice of any material to a sewer    or    pumping main  is the durability which will depend upon factors such as abrasion resistance, resistance to chemical attack and integrity of lining, coating and jointing systems.
5. Long term material changes: Details of the past performance of any material for any given application and set of circumstances will usually provide a useful indication of future performance. Historical data on materials on performance of materials should be reviewed wherever possible, for future reference.
6. Resistance to chemical attack: Sulphate and acids. in sewage and groundwater present the main threat to cement pipes and cement linings. Domestic sewage is normally slightly alkaline but there have been problems associated with septicity.
7. Abrasion resistance: Loss of the pipe material takes place due to abrasion by the gritty particles in the sewage. The abrasion resistance of cement concrete of pipes is influenced by the degree of compaction of the concrete and hardness of aggregates. Of the polymeric materials polyethylene has proved to be the most abrasion resistance