Installation of Gas Piping and Tubing Systems
Domain 3 - Installation of gas piping and tubing systems
This domain tests materials, jointing, support, burial, appliance connections, sizing and pressure testing. It is the most hands-on part of the G2 exam and the most likely place for a single wrong number to cost several marks.
Materials and joints
- Schedule 40 black steel is the standard above-ground material; copper ACR tubing and listed CSST are permitted with the manufacturer's fittings and rules.
- Threaded joints use listed gas-rated compound or tape on the male threads, leaving the first two threads clean; tighten, never back off a fitting to align it.
- CSST must be bonded to the electrical grounding system, typically with minimum 6 AWG copper, exactly as the manufacturer requires.
- Protect pipe from corrosion, vibration and physical damage; sleeve it where it passes through masonry or concrete.
Support, burial and appliance connections
- Support at intervals not exceeding about 3 m (10 ft) and near changes of direction; the pipe must not sag or load the appliance connector.
- Buried piping needs a minimum 375 mm (15 in) of cover, coating or wrapping, anodeless risers, greater depth under vehicle traffic, and a pressure test before backfill.
- Each appliance gets an accessible manual shutoff in the same room, a union or flange, and a sediment trap - a tee with a capped nipple of at least 3 in - as close as practicable and downstream of the shutoff.
- Appliance connectors are limited to 1.8 m (6 ft), must not be concealed or pass through walls, floors or ceilings, and must not be under tension or kinked.
Sizing
Use the B149.1 capacity tables with the total equivalent length from the meter or regulator to the farthest appliance, the total connected input, and the allowable pressure drop (0.5 in w.c. on a 7 in w.c. natural gas system). The tables assume a normal number of fittings; add equivalent length for extra elbows and tees.
Testing
Prove the piping with air or nitrogen before the meter is connected: typically 5 psi (35 kPa) for 15 minutes with no drop, on a gauge suited to the test range. Isolate the appliance so test pressure never reaches the gas valve. Once gas is on, leak-test joints at operating pressure with soap solution or an electronic detector - never a flame.
Worked example
A dryer connection sits 8 ft from where the rigid line currently ends. A 6 ft connector will not reach, so the answer is not a longer connector: extend the black steel to within 6 ft of the appliance connection, fit the shutoff valve and sediment trap, then install the connector with slack but no strain.
Traps
Rounding the measured run down to a shorter table column; forgetting that fittings add equivalent length; leaving CSST unbonded; burying copper for natural gas where sulfur corrosion is a risk; and pressure-testing with the appliance still connected.