Materials and Pipework Systems
This domain tests whether you can select a material that suits the water, the temperature, the pressure and the installation method - and explain why the alternative would fail.
Metallic systems
Copper to EN 1057, usually R250 half-hard, is joined by capillary soldering with lead-free solder, by press fittings, or by compression. Stainless steel to EN 10312 suits aggressive or high-chloride water. Galvanised steel is confined to older systems and needs dielectric separation from copper.
Plastics
- PEX (EN ISO 15875) and PE-RT for hot and cold; flexible, requires inserts, joined by manifold or push-fit.
- PP-R and CPVC for higher temperatures and chemical resistance.
- uPVC (EN 1452) and ABS for soil and waste.
- MDPE/PE100 (EN 12201) for buried service pipes.
Why materials fail
Galvanic corrosion where dissimilar metals touch; dezincification of ordinary brass in aggressive water (specify DZR); pitting from flux residues or chlorides; crevice corrosion under gaskets; erosion-corrosion at high velocity; UV degradation of plastic left exposed.
Movement and support
Plastics expand roughly ten times as much as copper, so they need more clips, offsets and expansion loops. Copper needs support to stop sagging and vibration.
Worked example
A hot tap body fails by dezincification after four years in a soft, low-alkalinity supply. The original brass was not dezincification-resistant. Reason from the evidence: the failure is on the hot side, where the water is more aggressive and the body thinner. Specify a DZR or lead-free DZR tap body and check compatibility of brass fittings on the same system.
Traps that cost marks
Joining copper to steel without a dielectric union; mixing insert types between push-fit brands; burying a joint in a wall without access; choosing ordinary brass in a soft-water area.