Pipe Joining, Threading, Bending and Fixing Techniques
Scope
This domain tests joint selection and execution: threaded GI, solvent-welded PVC/CPVC, soldered copper, compression and push-fit, plus bending and supporting pipe. Marks are lost when the joint type does not match the material or service.
Core rules
- Cut square, deburr and ream; a burr reduces flow and can damage a die or seal.
- GI threads are BSP tapered, about 1:16; use cutting oil, reverse the die to clear swarf, and check with a matching fitting. Do not bottom the fitting on the thread.
- PVC/CPVC solvent welding: dry-fit, clean with primer, apply cement to both surfaces, push and quarter-turn, hold, then allow full cure before pressure.
- Copper soldering: clean to bright metal, apply flux sparingly, heat the fitting, feed solder into the joint gap, do not overheat.
- Compression: insert the olive squarely and tighten firmly, not excessively.
- Bends: use a bending spring for copper or approved heat methods for plastic; respect minimum bend radius and support changes of direction.
- Fix with clips at recommended spacing and allow expansion loops on hot lines.
Worked example
Thread a 1/2-inch GI pipe. Cut with a hacksaw, ream the bore, clamp in a pipe vice, fit a 1/2-inch BSP die, oil the die, cut two or three turns, back off to clear swarf, then continue. Test with a coupling: the thread should engage about three to four turns and tighten without wobble. If the thread is too long, the pipe enters too far and may crack the fitting; if too short, it leaks.
Traps
Do not solvent-weld wet pipe; do not skip primer; do not over-tighten plastic threads; do not heat PVC with an open flame; do not leave flux residue, which corrodes copper.