Pipe materials and fittings - cutting, bending, threading, jointing
Pipe materials and fittings
The paper expects you to match a material to service conditions and to describe the correct jointing sequence.
Materials
- GI steel (IS 1239, light/medium/heavy): water and gas lines, screwed BSP taper joints; coat cut threads with zinc-rich paint to restore protection.
- CI (IS 1729): soil, waste and rainwater stacks; brittle, joined by lead-caulked socket or rubber ring.
- PVC/UPVC (IS 4985 for potable water): cold water and SWR drainage; solvent cement or rubber ring; never for hot water.
- CPVC: hot and cold water, chlorinated supplies; needs CPVC-specific solvent cement.
- Copper: capillary solder, compression or push-fit; annealed copper bends easily; use a dielectric union against steel to stop galvanic corrosion.
- HDPE: flexible coiled pipe for underground mains, borewells and agriculture; butt fusion, electrofusion or compression fittings.
Cutting, bending, threading
Plastic pipe cutter or fine-tooth saw for PVC/CPVC, then deburr and chamfer. Copper tube cutter with reamer. GI and CI by hacksaw or wheel cutter. Bend GI by packing with dry sand, heating and bending over a former; bend PVC with hot water or hot sand fill; anneal copper before bending.
Worked example
Choose materials for three lines: (a) hot water at 65 °C, (b) a 100 mm soil stack, (c) a 400 m buried farm main. Reasoning: PVC softens at hot-water temperature, so (a) is CPVC or copper; (b) is SWR PVC or CI; (c) needs flexibility and long lengths with few joints, so HDPE.
Traps that cost marks
Solvent cement on a wet or dirty pipe; PVC specified for hot water; no PTFE tape or hemp on screwed joints; skipping the reamer; direct copper-to-steel contact.