Pipework Fabrication, Jointing and Fixing (Metal and Plastic)
Domain focus
This domain tests cutting, bending, threading, jointing, fixing and supporting metal and plastic pipework. It covers GI, copper, uPVC, PPR, CPVC and HDPE, plus the jointing method each requires.
Core rules
- Cut square, deburr and keep the bore clear; remove swarf before jointing.
- GI: cut tapered threads, apply PTFE tape or approved dope to the male thread, engage fully but do not over-tighten.
- Copper: clean and flux before soldering; heat evenly; use press fittings only with the correct tool and jaw.
- uPVC: use primer and solvent cement on clean, dry surfaces; assemble with a quarter-turn and hold; allow full cure.
- PPR/HDPE: use the correct fusion welder, temperature and heating time; do not rotate after fusion.
- Support at recommended spacing and allow expansion; protect joints from stress.
Worked example
A pipe is measured between two socket fittings as 600 mm. Each socket depth is 18 mm, so cut length = 600 − (2 × 18) = 564 mm. The reasoning is that the pipe must insert fully into both sockets; cutting 600 mm would leave no expansion gap and stress the joints.
Traps
Jointing wet pipe; insufficient solvent cure; mixing PPR fittings with uPVC; using too much tape; forgetting dielectric unions between copper and GI; not allowing for thermal expansion.