Piping Materials, Fittings, Joints, and Supports
Matching Material to Application
Candidates must know which materials are approved for potable water, drain-waste-vent (DWV), and gas, and where each is prohibited. Common potable materials include copper, PEX, CPVC, and galvanized steel; lead and some plastics are prohibited. DWV commonly uses PVC, ABS, cast iron, and copper. Gas piping uses black steel, corrugated stainless steel tubing (CSST), and approved yellow polyethylene for burial.
Joints and Connections
Each material has approved joining methods: soldered or brazed copper, solvent-cemented plastic, threaded steel, push-fit, and mechanical couplings. Traps in questions include mixing incompatible materials (steel into copper without a dielectric union causes galvanic corrosion), using the wrong solvent cement for the plastic, and soldering near a valve without heat protection. Dielectric unions are required where dissimilar metals meet.
Supports and Protection
Support spacing depends on pipe size and material. Plastic DWV needs more frequent support than steel; copper needs hangers that do not damage the tube. Questions often test support spacing, protection from freezing, and protection at penetrations (sleeves, firestopping). Horizontal drainage piping also needs proper slope, which is a support concern because sagging creates bellies.
Rule of Thumb
Match the material, the joining method, and the support spacing to the same code table. If a question mixes two systems (for example, a copper supply feeding a steel water heater), look for the dielectric fitting as the answer.
Worked Example
A copper line connects directly to a steel tank. The fix is a dielectric union or approved insulating fitting at the connection to break the galvanic path. Without it, the steel corrodes and the joint fails.