--- title: "Good pipe requirements; expansion joint" subject: "Water Supply Engineering" chapter: 8 key: "semester_5/water_supply_engineering:pipe-requirements-expansion-joint" source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/pipe-requirements-expansion-joint site: BCT Engineering --- # Good pipe requirements; expansion joint Water Supply Engineering · Chapter 8: Conveyance of Water - Asked in: 2080 Bhadra, 4 marks; 2078 Bhadra, 2+2 marks (asked 2 times) - Video: [Thermal Expansion in Piping Systems: Challenges and Solutions Explained](https://www.youtube.com/watch?v=TXhdS8vya74) — PipingStress - 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-requirements-expansion-joint - Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-8 ## Question What are the requirements of a good pipe? Explain the expansion joint (its purpose and use in CI pipes) with a neat sketch. ## Short answer A good pipe must withstand internal/external loads, be durable with smooth interior, safe for water, have easy watertight joints, be light, low-cost, and repairable. An expansion joint allows thermal movement; a spigot slides in a socket with packing compressed by a gland, used on long CI lines, bridges, and near pumps. ## Answer #### Requirements of a good pipe 1. **Strength:** withstands internal pressure, water hammer and external loads (soil, traffic). 2. **Durability:** long life, resistant to corrosion, chemical attack from soil and water, and to abrasion. 3. **Smooth interior:** high Hazen-Williams C value, low friction loss, and no growth of deposits. 4. **Safe for water:** no taste, colour, toxic or bacterial effect on the water carried. 5. **Easy joints:** watertight, flexible and quick to make. 6. **Light and easy to handle** and transport; available in many sizes and lengths. 7. **Low cost,** including laying and maintenance, and locally available. 8. **Easy to repair,** to tap for connections, and to extend later. #### Expansion joint Pipes expand when the temperature rises and contract when it falls. In a long, rigid line this movement causes stress, buckling or joint leakage. An **expansion joint** lets the pipe move freely along its axis. - **Purpose:** to absorb the thermal expansion and contraction, and small ground settlement, without damaging the pipe or leaking. - **Use in CI pipes:** provided on long straight exposed pipelines, pipes on bridges and piers, near valves and pumps, and where pipes cross building joints. Spaced at about 30–50 m. ```text bolt gland packing +-----+ +---------+ ____|____ ====| |=======| gland |==| socket |==== pipe spigot slides <--> lead/rubber ring spigot end moves inside the socket ``` - The spigot end of one pipe enters a special socket (stuffing box). A rubber or lead packing fills the annular gap and a **gland** pressed by bolts compresses it to keep the joint watertight. - When the pipe lengthens or shortens, the spigot slides in the socket by 10–20 mm, while the packing keeps the water in. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A good pipe should withstand: A. Only its own weight B. Internal pressure, water hammer and external loads C. Only low pressure D. Nothing special Answer: B. Strength covers internal pressure, water hammer and soil/traffic loads. (Key point: Strength requirement) 2. What problem do expansion joints prevent in a long rigid line? A. Stress, buckling or leakage from temperature movement B. Corrosion C. Low flow D. Noise Answer: A. Thermal expansion and contraction would otherwise cause stress, buckling or joint leaks. (Key point: Why expansion joint) 3. Where are expansion joints provided in CI lines? A. Only at the source B. Buried short pipes C. Inside valves D. Long exposed lines, bridges, near valves and pumps, spaced about 30-50 m Answer: D. They are used on long exposed straight lines, bridges and near valves, pumps, roughly every 30-50 m. (Key point: Use in CI pipes) 4. What does the gland do? A. Cuts the pipe B. Compresses the packing to keep the joint watertight C. Measures flow D. Anchors the pipe to rock Answer: B. Bolts press the gland, compressing the rubber or lead packing around the spigot. (Key point: Role of gland) ## 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 requirements; PE, PVC, PPR pipes](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-requirements-pe-pvc-ppr) — Water Supply Engineering, chapter 8 - [Pipe joints; expansion joint](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-joints-expansion-joint) — Water Supply Engineering, chapter 8, asked 3× - [Requirements of a good pipe material](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Arequirements-good-pipe-material) — Water Supply Engineering, chapter 8, asked 2× - [Expansion joint and flanged joint](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aexpansion-flanged-joint) — Water Supply Engineering, chapter 8, asked 2× - [Short note: GI and CI pipe](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Agi-ci-pipe-note) — Water Supply Engineering, chapter 8 ## Related in other subjects - [Why joints are necessary; expansion joint](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ajoints-why-expansion) — Building Technology, chapter 10, asked 2× - [Expansion joint in a residential building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexpansion-joint-350wall) — Building Technology, chapter 10 - [Requirements of SI and CI engine fuels](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Asi-engine-fuel-requirements) — Automotive Technology, chapter 2 - [Good insulating material requirements and applications](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Ainsulating-requirements-application) — Electric Machine Design, chapter 1, asked 2×