- 2072 Asoj · 8 marks
Sewer pipe materials: merits, demerits
Short answer
Sewer pipes include asbestos cement, cast iron, concrete, vitrified clay, plastic (PVC/HDPE), brick, and steel. Concrete is economical in large diameters but susceptible to acids; vitrified clay resists corrosion but is brittle; plastic is smooth and light but weak under loads. For large sewers RCC, for small ones HDPE/UPVC or stoneware are common.
List the various types of pipe materials used in sewer line. Describe them with merits and demerits.
Sewers are made of materials that must be strong, smooth, watertight, durable against sewage gases and acids, and economical. The common materials are given below.
1. Asbestos cement (AC) pipes
- Merits: light, easy to cut and lay, smooth inside (low friction), available in long lengths with few joints, resistant to corrosion.
- Demerits: weak against impact and heavy loads; attacked by acids and sulphates; health concern about asbestos fibres, so use is declining.
2. Cast iron (CI) pipes
- Merits: strong, durable, withstand high internal and external pressure and heavy traffic; long lengths; good for river crossings, inverted siphons, pumping mains.
- Demerits: costly, heavy; corrodes with sewage and acids unless lined; rough surface after rusting.
3. Concrete pipes (plain and reinforced, PCC and RCC)
- Merits: cheap, can be made at site in large sizes (up to 3 m), strong when reinforced, easy to repair, and widely available in Nepal.
- Demerits: attacked by acid wastes and hydrogen sulphide (crown corrosion), porous, heavy to transport, many joints in small lengths.
4. Vitrified clay / stoneware pipes
- Merits: resistant to acids and corrosion, smooth, impervious, durable, cheap in small sizes.
- Demerits: brittle and weak in tension, break in handling; available only in small sizes (up to 600 mm) and short lengths, so many joints.
5. Plastic pipes (PVC, HDPE, UPVC)
- Merits: very light, smooth (lower slope needed), corrosion free, flexible joints, long lengths, easy installation; popular for house connections and small sewers.
- Demerits: low strength under heavy loads and shallow cover; damaged by heat and sunlight; costly in large sizes.
6. Brick and stone masonry sewers
- Merits: can be built in any shape and large size at site using local material.
- Demerits: joints leak, rough surface, attacked by sewage, slow to construct, so used only for large old sewers with lining.
7. Steel pipes
- Merits: strong, light compared to CI, can have long lengths, welded watertight joints; used for pressure mains and siphons.
- Demerits: corrode easily (need lining and coating), costly.
For a modern urban sewer in Nepal, RCC pipes are used for large diameters, and HDPE/UPVC or stoneware for small ones.
✓ Answer checked by Claude Opus 5.5 (high effort)
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