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Three pipe materials with merits/demerits
Short answer
Cast iron/ductile iron is strong, durable but heavy and costly; galvanised iron is cheap, easy to thread but corrodes; PVC/HDPE is light, non-corroding, smooth, but weak under high pressure and UV-sensitive.
Enlist three materials commonly used for water supply pipe. Also describe their merits and demerits.
Three materials which are commonly used for water supply pipes are cast iron / ductile iron (CI/DI), galvanised iron (GI) and polyvinyl chloride (PVC) / HDPE plastic.
| Material | Merits | Demerits |
|---|---|---|
| Cast iron / ductile iron | Strong, long life (100 years), stands high pressure and external loads, resists corrosion better than steel, easy to cut and join (socket-spigot, flanged) | Heavy, costly, brittle (CI breaks by shock; DI is tougher), tuberculation and loss of capacity with age, so cement lining is needed |
| Galvanised iron (GI) | Cheap, strong, easy to cut, thread and fit, good for small diameters up to 150 mm, rigid and good for exposed pipes | Corrodes with time (zinc coating is lost, especially in acidic soft water), scale deposits cut the flow, limited length, heavy, life 15–30 years |
| PVC / HDPE | Light, easy to handle and lay, non-corroding, smooth interior (C = 140–150), low cost, long life, quick to join (solvent cement or fusion), HDPE is flexible for hilly ground | Low strength against high pressure and impact, damaged by sun and heat (UV) and by freezing, large expansion, cannot be used on exposed lines without covering, special solvent/fusion skills needed |
Steel, concrete and asbestos-cement pipes are used for large mains but are less common in small Nepali schemes.
✓ Answer checked by Claude Opus 5.5 (high effort)
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