--- title: "Three pipe materials with merits/demerits" subject: "Water Supply Engineering" chapter: 8 key: "semester_5/water_supply_engineering:pipe-materials-merits-demerits" source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/pipe-materials-merits-demerits site: BCT Engineering --- # Three pipe materials with merits/demerits Water Supply Engineering · Chapter 8: Conveyance of Water - Asked in: 2080 Baisakh, 4 marks; 2078 Kartik, 3 marks; 2075 Chaitra, 4 marks; 2073 Shrawan, 4 marks (asked 4 times) - Video: [Types of Pipes Used in Water Distribution | Water Supply System | Environmental Engineering | Mohan](https://www.youtube.com/watch?v=aYEIzp9-ah0) — Digitech education - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/pipe-materials-merits-demerits - Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-8 ## Question Enlist three materials commonly used for water supply pipe. Also describe their merits and 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. ## Answer 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which set is the three commonly used materials? A. CI/DI, GI and PVC/HDPE B. Brass, copper and lead C. Concrete, clay and wood D. Steel, glass and rubber Answer: A. The answer lists CI/DI, GI and PVC/HDPE. (Key point: Three materials) 2. Which is a demerit of cast iron? A. Very short life B. Cannot take pressure C. Heavy, costly and brittle, with tuberculation reducing capacity D. Corrodes more than steel Answer: C. CI is heavy, costly, brittle, and tuberculation needs cement lining. (Key point: CI demerit) 3. Why does GI have a limited life of 15 to 30 years? A. It is too weak to cut B. It cannot be threaded C. It is plastic D. Zinc coating is lost by corrosion, especially in acidic soft water Answer: D. GI corrodes once the zinc coating is lost, and scale cuts the flow. (Key point: GI weakness) 4. Which is a merit of PVC/HDPE and a demerit? A. Smooth interior (C = 140-150); damaged by UV and heat B. Very high pressure strength; corrodes C. Heavy; cheap D. Brittle on impact only; light Answer: A. Plastic is light, non-corroding and smooth, but weak against UV, heat and impact. (Key point: Plastic pipes) ## Related in Water Supply Engineering - [Distribution layouts, merits and demerits](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adistribution-layouts-merits-demerits) — Water Supply Engineering, chapter 7, asked 6× - [Objectives of water supply and components](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aobjectives-ws-rural-diagram) — Water Supply Engineering, chapter 1, asked 3× - [Objectives of supply; wholesome water requirements](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aobjectives-requirements-wholesome) — Water Supply Engineering, chapter 1, asked 2× - [Importance and objectives of water supply](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aimportance-objectives-ws) — Water Supply Engineering, chapter 1 - [Pipe material factors; CI vs steel](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-material-factors-ci-steel) — Water Supply Engineering, chapter 8 - [Typical water supply system and components](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Atypical-ws-system-components) — Water Supply Engineering, chapter 1, asked 4× ## Related in other subjects - [Sewer pipe materials: merits, demerits](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asewer-pipe-materials) — Sanitary Engineering, chapter 3 - [Merits and demerits of lime mortar](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Alime-mortar-merits-demerits) — Civil Engineering Materials, chapter 6 - [Reactors in stations: merits and demerits](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Areactors-merits-demerits) — Power Plant Equipment, chapter 4 - [Cofferdam types, uses, merits and demerits](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Acofferdam-types-merits) — Foundation Engineering, chapter 5, asked 7×