Gas Pressure Testing Reference

Why this matters

Gas leaks kill. The pressure test is the verification that a gas system is sealed - required by code on every install, repair, and modification. The tech who tests properly catches leaks before turning on gas. The one who shortcuts can release gas into a customer's home + create explosion or asphyxiation risk. This is the field card.

When pressure testing is required

Per NFPA 54 / IFGC:

• New gas piping installation
• Any modification, extension, or repair to existing piping
• After replacement of any appliance or fitting
• Before initial turn-on of gas to any new equipment
• After any incident that may have compromised the system (impact, fire, etc.)

Local code may have additional requirements. The inspector wants documentation that a test was performed + passed before sign-off.

Types of pressure tests

Air or nitrogen pressure test (standard): required for new installations + modifications. System pressurized with inert gas to test pressure; observed for pressure drop.

Soap solution test (final check): at each joint with system pressurized; bubbles indicate leak. Used after pressure test passes, for any final assembly.

Electronic leak detector (gas-on test): with actual gas in system, sweep joints with combustible gas detector. Used for in-service systems + final verification.

NEVER use a match or flame to test for gas leaks.

Test pressures by code

Per NFPA 54 / IFGC:

• Residential, working pressure ≤ 14" WC (most homes): 3 PSI for 10 minutes, OR 1.5x working pressure for 30 minutes - minimums vary by jurisdiction; check local
• Working pressure > 14" WC (typical of CSST systems or some commercial): 5 PSI for 10 minutes minimum, OR higher per spec
• Commercial / industrial systems: higher pressures, longer durations, per specific code

The test pressure is HIGHER than working pressure (1.5x rule typical) to provide a safety margin. Gauges with appropriate range required.

Test equipment

Gauge: range appropriate to test pressure. A 30 PSI gauge resolves 3 PSI well; a 100 PSI gauge resolves 3 PSI poorly. Match the gauge to the test.

Pressure source: hand pump, compressed air OR nitrogen tank with regulator. Air OK for most residential; nitrogen preferred for high-quality work + commercial.

Manometer (water column): for low-pressure systems (working pressure measurements + leak verification). Reads in inches of water column (" WC).

Soap solution: commercial leak detector liquid (CertaSeal, Gas Trac, etc.) OR dish soap + water. Apply with brush.

Electronic combustible gas detector: for in-service verification. Range covers methane + propane.

Test procedure (typical residential)

Setup:

1. Isolate the section to be tested (cap or shut off appliances)
2. Verify all valves serving the test section are CLOSED (don't pressurize utility-side or downstream of test boundary)
3. Install gauge at convenient point
4. Connect pressure source (hand pump or regulated nitrogen)

Pressurize:

1. Bring system to test pressure (e.g., 3 PSI)
2. Hold briefly (1 - 2 minutes) to allow temperature equilibrium
3. Verify gauge reading stable

Observe:

1. Note starting pressure + time
2. Wait the required test duration (10 minutes typical)
3. Note ending pressure
4. Acceptable result: 0 PSI drop (some jurisdictions allow small drop for temperature change)

Locate leak (if pressure drops):

1. Apply soap solution to each joint
2. Watch for bubbles (small leak makes slow bubbles; bigger leak makes rapid foam)
3. Mark the leak location
4. Depressurize, repair, retest

Final verification:

1. After all joints OK + system holding pressure for full test duration, release pressure
2. Document the test on permit / inspection paperwork
3. Inspector witnesses the test in some jurisdictions

Temperature effects on pressure test

Pressure changes with temperature. Gas law: pressure increases ~ 1% per 5°F temperature rise.

If a test is performed outdoors in winter:

• System pressurized at 30°F = at one pressure
• Test duration of 30 min - temperature might rise OR fall
• Apparent "leak" may just be temperature change

For longer tests in changing temperatures, factor this in. Some jurisdictions allow small drops attributable to temperature; others don't. Document the temperature.

What to do if pressure drops

Slow drop (small leak):

1. Soap test each joint
2. Find + mark
3. Repair (re-thread + re-dope, OR re-flare, OR repair fitting)
4. Retest the section
5. Document the repair

Rapid drop (large leak):

1. Stop the test
2. Verify isolation valves are correct (often the "leak" is actually wrong valve open)
3. Soap test prominent joints
4. Inspect for missing OR damaged components
5. Repair + retest

No-bubble leak (very slow):

1. Could be small enough that soap won't show it
2. Hold pressure longer; verify slow drop
3. Use electronic leak detector around joints in addition to soap
4. Methane (natural gas) detector sensitive to tiny leaks once gas is in system

Common leak locations

• Threaded joints where pipe dope failed (insufficient dope, wrong dope for gas)
• Threaded joints where wrong PTFE tape was used (white "plumber's" tape vs yellow "gas" tape - gas tape required)
• Loose union connections
• Damaged flare fittings (over-tightened crushed flares are common)
• CSST connections where the fitting wasn't fully seated
• Drips at brass valve packing
• Damaged threads on cut-+ -reused pipe
• Pinhole in pipe (rare; corrosion or damage during install)

The leak location is also instructive: most leaks are at joints, very few in mid-pipe. Pipe damage requires significant external cause.

Sealants + dope for gas

Yellow PTFE tape (gas-rated): thicker density; rated for gas service.

Pipe dope rated for gas: Rectorseal #5, Loctite 567, Permatex 80632 - must say "gas" on the label.

DO NOT use white plumbing PTFE tape on gas. Won't seal reliably + isn't rated.

Don't use Teflon paste / silicone: not gas-rated.

Apply pipe dope correctly: clockwise around male threads, leaving the first 2 threads bare to prevent dope contamination of the gas stream. Tighten until snug + then 1 - 2 turns past. Don't over-tighten.

CSST specifics

Corrugated stainless steel tubing for gas distribution:

• Manufacturer-specific fittings ONLY (not interchangeable across brands)
• Bonding to grounding system REQUIRED per NFPA 54 (lightning strike protection)
• Pressure testing same procedure as black iron
• Don't bend below manufacturer's minimum radius (kinks compromise integrity)

Working pressure verification (after gas-on)

After the system passes pressure test + is in service:

Manifold pressure: measure with manometer at the appliance gas valve outlet

• Natural gas: 3.5" WC typical
• Propane: 10" - 11" WC typical

References

• NFPA 54 (National Fuel Gas Code)
• NFPA 58 (Liquefied Petroleum Gas Code)
• IFGC (International Fuel Gas Code)
• IRC Chapter 24 (Fuel Gas)
• Manufacturer technical data (Rectorseal, gas valve manufacturers)
• Manuall internal: Gas Line + Propane Sizing Reference, Common Pipe Fittings