Plumbing Materials
This domain tests material identification, selection and the IS standard behind each pipe, plus the faults that follow a wrong choice.
Core rules and concepts
- GI (IS 1239 Part 1) comes in light, medium and heavy classes. Zinc coating resists corrosion; joints are threaded. Not advised for concealed hot lines because heat and condensation destroy the coating.
- Cast iron (IS 1726) is used for soil, waste and vent stacks, joined by lead caulking or rubber rings. Strong and quiet but heavy and brittle.
- UPVC (IS 4985) for cold potable water, solvent welded. CPVC for hot water up to about 90 °C. SWR (IS 13592) for soil and waste drainage. HDPE for underground mains and borewell delivery, joined by butt fusion. PPR for hot water. Copper for hot water and medical gas.
- Plastic expands roughly ten times more than steel per degree rise, degrades under UV, and needs closer supports and expansion loops.
- Do not couple GI directly to copper; the joint corrodes galvanically. Use a dielectric union.
Worked example
Choose materials for three items. (a) Concealed hot water line in a bathroom: CPVC, solvent cement joint, wrapped insulation. (b) 100 mm external soil stack: SWR UPVC with rubber ring joints, UV-stabilised, two clamps per floor. (c) 300 m borewell delivery main: HDPE, butt fusion, pressure class checked against pump head. The reasoning is that temperature, exposure and joint method decide the material, not price alone.
Traps that cost marks
- Specifying SWR pipe for a hot water line.
- Using ordinary UPVC outdoors in direct sun.
- Joining two different plastics with the wrong solvent cement.
- Ignoring pressure de-rating of plastic pipes at higher temperature.