---
title: "Short note: GI and CI pipe"
subject: "Water Supply Engineering"
chapter: 8
key: "semester_5/water_supply_engineering:gi-ci-pipe-note"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/gi-ci-pipe-note
site: BCT Engineering
---

# Short note: GI and CI pipe

Water Supply Engineering · Chapter 8: Conveyance of Water

- Asked in: 2070 Chaitra (old course)
- Video: [24. Types of Metallic Pipes || Water supply Engineering](https://www.youtube.com/watch?v=DcuSJYB3X0s) — NITIANS ACADEMY
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/gi-ci-pipe-note
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-8

## Question

Write a short note on GI and CI pipe.

## Short answer

GI pipe is galvanized steel, strong, cheap, used for house connections, joined by threaded sockets; it corrodes over time and life is 15–30 years. CI pipe is cast iron, very durable (100 years), corrosion-resistant, heavy, brittle, socket-spigot joints, prone to tuberculation unless lined.

## Answer

#### Galvanised iron (GI) pipe
GI pipe is a steel pipe coated with a layer of zinc (galvanised) to protect it from rust.
- Available in sizes 15–150 mm in 6 m lengths in three classes (light, medium, heavy).
- Jointed by threaded sockets, unions, bends and tees (screwed joints).
- **Merits:** strong, rigid and cheap; can take high pressure; easy to cut and thread; good for exposed lines, house connections and stream crossings.
- **Demerits:** corrodes and scales (zinc is lost), especially in acidic or soft water, so the flow and the life (15–30 years) are reduced; heavy; limited to small sizes.

#### Cast iron (CI) pipe
CI pipe is cast from grey iron in lengths of 3–6 m with a socket at one end.
- Used for distribution mains of 80 mm and larger.
- Jointed by socket-spigot (lead and yarn), flanged or mechanical joints.
- **Merits:** very long life (100 years), resists corrosion (better than steel), stands high pressures and external loads, easy to cut and tap.
- **Demerits:** heavy, brittle (breaks under shock or uneven settlement), costly, and the interior roughens with tuberculation unless cement-mortar lined.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is GI pipe?
   A. Wrought iron coated with tar
   B. Plastic with iron core
   C. Cast iron with lead coating
   D. Steel pipe coated with zinc to prevent rust
   Answer: D. GI is galvanised: steel coated with zinc. (Key point: GI definition)

2. Why is the life of GI pipe reduced in acidic or soft water?
   A. It becomes brittle
   B. Joints leak by threads
   C. Zinc is lost, so it corrodes and scales
   D. It softens
   Answer: C. Loss of zinc exposes the steel to corrosion and scaling, reducing flow and life (15-30 years). (Key point: GI demerit)

3. Which is a demerit of CI pipe?
   A. Used only below 80 mm
   B. Short life of 15 years
   C. Brittle, breaking under shock or uneven settlement
   D. Cannot be tapped
   Answer: C. CI is brittle and heavy; it also tuberculates unless cement lined. (Key point: CI demerit)

4. How are CI pipes commonly jointed?
   A. Heat fusion
   B. Solvent cement
   C. Socket-spigot (lead and yarn), flanged or mechanical joints
   D. Screwed sockets only
   Answer: C. CI pipes have a socket at one end and use socket-spigot, flanged or mechanical joints. (Key point: CI jointing)

## Related in Water Supply Engineering

- [Pipe requirements; concrete, CI, PPR pipes](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-requirements-concrete-ci-ppr) — Water Supply Engineering, chapter 8
- [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
- [Good pipe requirements; expansion joint](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-requirements-expansion-joint) — Water Supply Engineering, chapter 8, asked 2×

## Related in other subjects

- [RCC slab culvert: brick, wearing coat, GI pipe, steel](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aslab-culvert-a-fig-b) — Estimating and Costing, chapter 6