Gas Line Pressure Test + Leak Detection SOP
Why this matters
Gas line pressure testing is the safety procedure that separates the licensed gas-piping contractor from the unlicensed handyman who installs a stove + creates a slow leak. A gas leak in residential plumbing kills - every year in U.S., 5 - 15 fatal house explosions from undetected gas leaks. Every gas line install, repair, OR meter swap REQUIRES a pressure test per IFGC + state code; AHJ inspector verifies + signs off. The plumber who tests properly + documents the test creates a paper trail that protects the customer + the contractor; the plumber who skips OR shortcuts the test creates an explosion waiting to happen.
When pressure test required
Per IFGC (International Fuel Gas Code) + state amendments:
- New gas line install (whole system OR single appliance branch)
- Modification of existing gas line (add appliance, relocate, repair)
- After gas meter swap by utility
- Suspected leak (customer complaint, gas smell)
- Annual safety inspection (recommended; not always code-required for residential)
Most jurisdictions require AHJ inspector to witness OR review test documentation before service restoration.
Pre-test preparation
Shut off utility supply at meter (or main valve before tested section).
Isolate appliances: disconnect OR install temporary plugs at appliance connections. Pressure test will damage appliance regulators if connected.
Verify all valves closed: at appliance shut-offs (each one) + at any branches.
Equipment:
- Calibrated test gauge (low-pressure 0 - 30 PSI; calibrated annually)
- High-pressure gauge for utility supply test (0 - 100 PSI)
- Pressure relief valve on test rig (safety)
- Plugs / caps for open ends
- Soap solution (50/50 dish soap + water) for leak detection
- Electronic gas detector (optional but recommended; combustible gas indicator)
Test pressures (residential, per IFGC)
| Gas type | Test pressure | Hold time |
|---|---|---|
| Natural gas (low pressure, 0.5 PSI service) | 3 PSI minimum, 10 PSI typical | 15 min minimum |
| Natural gas (medium pressure, 2 PSI+ service) | 10 PSI minimum | 30 min minimum |
| Propane (LP, 0.5 PSI service) | 10 PSI minimum | 15 min minimum |
| Propane (medium pressure) | 10 - 15 PSI | 30 min minimum |
| LP cylinder + appliance only | 15" WC OR 1.5x operating | 5 min minimum |
Higher than code minimum is acceptable. Many jurisdictions require 15 PSI for 15 minutes regardless of category.
Critical rule: NEVER test gas line with high pressure (above 15 PSI) without first removing or isolating appliance regulators + relief valves. The pressure spike will damage them.
Test procedure
- Connect test gauge via plugged test port or temporary tee
- Connect pressurization source (hand pump, regulated compressor, or nitrogen bottle)
- Pressurize SLOWLY to test pressure (spike cracks fittings)
- Hold required time (15 - 30 min per code); needle must NOT drop
- Inspect each joint with soap or gas detector while under pressure
- PASS = no loss over hold. Document gauge serial, test pressure, hold time, result, photos
- Bleed pressure to atmosphere OUTDOORS (never indoors)
- Restore appliance connections + verify normal supply
- Final leak check at each appliance with soap
PASS / FAIL
PASS: gauge steady throughout hold. FAIL: any drop ≥ 1 PSI in 15 min OR visible needle movement (slight drop at gauge connection only → fix connection + retest).
Locate the leak: listen for hissing (large), soap every joint working back from appliances, electronic detector probe, combustible-gas analyzer. Repair: tighten threaded 1/4 turn at a time + retest; re-solder + re-flux; replace defective fitting; CSST = replace fitting at end. Retest fully after every repair.
CSST + grounding (modern systems)
CSST (corrugated stainless steel tubing) is increasingly common 2010+:
Bonding + grounding (CRITICAL for modern CSST):
- All CSST systems must be bonded to ground per manufacturer + NEC
- Bonding clamp at meter + grounding electrode connection
- Skipping this = lightning-strike induced arcing failure + fire
- The "Counterstrike" CSST has manufacturer-built bonding
Brand-specific fittings: never mix Gastite, Tracpipe, OmegaFlex fittings - flares + nuts aren't interchangeable.
Black iron piping (traditional)
Thread sealant: code-approved pipe dope, NOT Teflon tape unless specifically rated for gas (yellow PTFE tape only). Many jurisdictions require gas-rated pipe dope only.
Sizing: per IFGC tables; sized by total CFH demand + run length. Undersized = appliance starvation.
Drip leg: required at each appliance connection (catches condensate + debris).
Common test failures
Leak at threaded fitting (most common): under-tightened OR over-tightened (cracked); apply correct dope; tighten to spec.
Leak at appliance shutoff valve: replace valve OR repack stem.
Leak at gas meter (utility side): not your responsibility; call utility.
Leak inside wall or floor cavity: requires opening drywall OR floor to access; major repair.
Gauge bouncing erratically: test rig vibration OR temperature variations OR leak; isolate.
Documentation
Per test: date + time, address + customer, plumber license + certification, gas type + service pressure, test pressure + hold time, pass/fail, gauge photos, AHJ signature if required. Filing: customer copy, permit file at AHJ, plumber records (7-yr retention minimum), some jurisdictions require online filing.
Service contract opportunity
Annual gas system check: visual inspection of all gas lines, pressure check at meter, leak detection at every appliance, combustion analysis, CO test in living space. Premium full safety inspection (water + gas + drain + venting) .
References
- IFGC International Fuel Gas Code (current edition + state amendments)
- NFPA 54 (National Fuel Gas Code; technically synonymous with IFGC)
- NFPA 58 (Liquefied Petroleum Gas Code)
- ANSI Z21 (Gas Appliance Standards)
- Local gas utility requirements (varies)
- Manuall internal: Gas Line Installation Reference, Annual Plumbing Inspection