Plumbing Materials
Domain 3 tests material families and selection: ferrous and non-ferrous metals, plastics, vitreous china, and jointing compounds, with the standards and limits that decide which one you may use.
Know the families
- GI steel (IS 1239): zinc coated in light, medium and heavy classes; strong but corrodes in soft or acidic water.
- Cast iron: brittle and heavy, still common for buried drainage, jointed with rubber gaskets.
- Copper: corrosion resistant, good for hot water, joined by soldering, brazing or press fittings.
- PVC-U: cold water only, around 60 °C limit; CPVC to about 93 °C; PPR to about 95 °C; HDPE is flexible with fused joints.
- Vitreous china for sanitaryware (IS 2556); brass for valves and fittings. Lead and asbestos cement are no longer acceptable.
Selection criteria
Temperature, pressure rating and its derating with temperature, water quality, buried or exposed, UV exposure, thermal expansion, cost, and whether matching fittings are available. Solvent cement must match the plastic, solder must be lead-free, and threads take PTFE tape or hemp with paste.
Worked example
A hot water line runs at 70 °C and 3 bar. Plain PVC-U would soften and sag, and its pressure rating falls sharply as temperature rises. CPVC is rated around 93 °C, so with the temperature derating factor applied, a CPVC pipe of the correct pressure class is specified, jointed with CPVC solvent cement, and supported to allow expansion.
Traps
Choosing by price only; using cold-water cement on CPVC; galvanised pipe on acidic borewell water; assuming the printed pressure rating applies at every temperature.