Piping, Fittings, and Pipe Joining
What this domain tests
This domain covers material selection and the joining methods that make a system reliable: copper, PVC, CPVC, ABS, PEX, galvanized steel, cast iron, and the fittings that connect them. You should know which joining method belongs to which material, what makes a joint fail, and how to protect dissimilar metals.
Core joining rules
- Copper: cut square, ream, clean, flux, and heat evenly with lead-free solder. Press fittings require a calibrated tool and full insertion. Brazing is used where higher temperature is needed, such as medical gas.
- PVC and ABS: use the correct solvent cement; PVC also needs primer. Apply cement to both surfaces, assemble with a quarter-turn, hold, and allow the proper cure time for temperature and humidity. CPVC requires CPVC-compatible cement.
- PEX: use the fitting system matched to the pipe-crimp, clamp, or expansion-and follow the manufacturer’s insertion and tool-calibration requirements. Protect PEX from UV and excessive heat.
- Steel: cut square, ream, thread with the correct die, and apply pipe dope or tape. Use a dielectric union between copper and steel to limit galvanic corrosion.
- Cast iron no-hub: use the specified coupling and torque; over-torque can distort the gasket.
Worked example
You must connect 3/4-in. copper to galvanized steel. Direct threading or soldering the two together creates a galvanic couple, and the steel side will corrode. The correct detail is a dielectric union or a brass transition fitting, with the copper tube cleaned and soldered using lead-free solder. Pressure-test the joint before closing the wall.
Traps that cost marks
Using PVC cement on CPVC, skipping primer on PVC, failing to ream copper or steel, soldering a line that is still wet, and over-tightening no-hub couplings. Another common error is ignoring fitting takeoff when calculating cut lengths.
Key points
- Match the joining method to the material and manufacturer’s system.
- Clean, ream, and square cuts before joining.
- Use primer with PVC and CPVC-compatible cement with CPVC.
- Use dielectric unions between copper and steel.
- Pressure-test before concealing joints.