Pipe Joining Methods and Jointing Techniques
Domain 7 tests matching a jointing method to its material and executing it so it passes a pressure test: threaded, solvent weld, fusion, compression, soldered, flanged and push-fit.
Match method to material
- GI and steel: taper thread, PTFE tape or hemp with paste, hand-tight then one or two turns with a wrench.
- PVC-U and CPVC: primer then solvent cement, even coat, quarter turn on insertion, hold, wipe, cure.
- HDPE and PPR: butt fusion, electrofusion or socket fusion; compression fittings on small sizes.
- Copper: lead-free solder with flux, or press and compression fittings.
- Cast iron: rubber gasket push-fit; lead caulking is obsolete.
Rules
- Surfaces clean, dry and square, with the pipe end chamfered.
- Cure time depends on temperature and diameter; no pressure test until fully cured.
- Hydrostatic test at 1.5 times working pressure before boxing in or concealing.
Worked example
A newly solvent-welded 32 mm line leaks at a joint under test. Reasoning: the leak is at a cemented joint, so the pipe was probably wet or dirty, too little cement was applied, or the line was pressurised before cure. More cement on the outside will not repair it; cut out the fitting, remake the joint with fresh cement, and wait the full cure before retesting.
Traps
Too much PTFE tape splitting the socket; soldering a pipe full of water; testing immediately after solvent welding; using PVC cement on CPVC.