8.3 Gas Pipe Inspection, Testing, & Purging

Gas Pipe Inspection, Testing, & Purging

1. Pre-Inspection & Appliance Isolation Mandates

Before fuel gas is introduced into new or altered piping, the system must undergo mandatory visual inspection and pressure testing under IFGC Section 406 and NFPA 54 Chapter 8. Pressure testing verifies structural integrity and proves that all threaded, brazed, welded, or mechanical joints are completely leak-free.

Appliance Isolation Requirement

Prior to pressurizing gas piping for testing, all connected gas appliances must be isolated from the piping system:

1. Appliance Shutoff Valves: Every individual appliance shutoff valve must be closed.
2. Disconnecting Appliance Control Valves: If the test pressure exceeds 0.5 psi ($14\text{ in. w.c.}$ or $3.5\text{ kPa}$), appliances must be physically disconnected from the piping and the pipe outlets capped or plugged.

WARNING: Automatic gas control valves, regulators, and solenoid valves inside gas appliances are engineered for low operating pressures ($< 14\text{ in. w.c.}$). Subjecting appliance controls to test pressures of $3\text{ psi}$ or $10\text{ psi}$ will rupture internal rubber diaphragms, destroy control valves, and create dangerous gas leakage when gas is turned on.

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2. Code Pressure Test Parameters & Gauge Calibration

┌────────────────────────────────────────────────────────────────────────────────────────┐
│                        FUEL GAS PRESSURE TEST PARAMETERS MATRIX                        │
├─────────────────────────────┬──────────────────────────┬───────────────────┬───────────┤
│ System / Material Type      │ Minimum Test Pressure    │ Minimum Duration  │ Test Media│
├─────────────────────────────┼──────────────────────────┼───────────────────┼───────────┤
│ Low-Pressure Metallic Pipe  │ 1.5x Working Pressure or │ 10 Minutes        │ Air, N2,  │
│ (Black Steel / Copper)      │ Min 3.0 psi (21 kPa)     │ (< 10 cu ft vol)  │ CO2, Inert │
├─────────────────────────────┼──────────────────────────┼───────────────────┼───────────┤
│ Corrugated Stainless Steel  │ Min 10.0 psi (69 kPa)    │ 10 Minutes        │ Air, N2,  │
│ Tubing (CSST)               │ (Or per Mfr Listing)     │                   │ CO2, Inert │
├─────────────────────────────┼──────────────────────────┼───────────────────┼───────────┤
│ Medium-Pressure Systems     │ Min 5.0 psi (34.5 kPa)   │ 10 Minutes        │ Air, N2,  │
│ (2.0 psi Distribution)      │                          │                   │ CO2, Inert │
├─────────────────────────────┼──────────────────────────┼───────────────────┼───────────┤
│ Large Volume Piping Systems │ 1.5x Working Pressure    │ 30 Min per 500    │ Air, N2,  │
│ (> 10 cu ft pipe volume)    │                          │ cu ft pipe vol    │ CO2, Inert │
└─────────────────────────────┴──────────────────────────┴───────────────────┴───────────┘

Approved Test Media

Test media are limited to compressed air, nitrogen, carbon dioxide, or an inert gas.

$\text{STRICT PROHIBITION: Oxygen } (O_2) \text{ MUST NEVER BE USED.}$

Introducing pure oxygen under pressure into a gas pipe containing trace hydrocarbon oils or thread sealants creates a high-risk explosive hazard capable of spontaneous ignition and catastrophic pipe explosion.

Pressure Gauge Resolution Rules

Model codes enforce strict limits on gauge selection to ensure minor pressure drops can be detected by inspectors:

$\text{Maximum Gauge Range} \le 5 \times \text{Test Pressure}$

• For a 3 psi test: The pressure gauge dial range cannot exceed 0 to 15 psi (with maximum $0.1\text{ psi}$ graduations).
• For a 10 psi test: The gauge range cannot exceed 0 to 50 psi.

Using a $0\text{--}100\text{ psi}$ gauge to perform a $3\text{ psi}$ gas test is a major code violation because a minor pressure drop of $0.5\text{ psi}$ is completely imperceptible on a high-range dial.

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3. Leak Detection Procedures & Approved Solutions

After pressurizing the piping system, all joints, fittings, valves, and connections must be tested using an approved liquid leak detector solution or electronic sniffer.

Non-Corrosive Bubble Test Requirement

Liquid leak detection solutions must comply with ASTM G188 and be certified non-corrosive.

Chemical Hazard: Standard household dishwashing soaps or detergents containing ammonia or chlorides must NEVER be used on brass or copper piping. Ammonia attacks the brass grain structure, causing severe stress-corrosion cracking (season cracking) that results in sudden catastrophic joint rupture months after testing.

Zero Pressure Drop Verification

The test pressure must hold steady with zero pressure drop for the entire test duration. If the pressure drops:

1. Coat all joints with non-ammoniated leak detector fluid and look for expanding bubble clusters.
2. Once the leak is identified, completely depressurize the piping system before making repairs.
3. Never attempt to tighten threaded fittings or compression nuts while the pipe is under pressure.
4. Re-pressurize the system and perform the complete 10-minute test from the beginning.

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4. Gas Line Purging Protocols & Explosive Limits

Purging is the controlled displacement of air inside a new piping system with fuel gas prior to commissioning, or the displacement of fuel gas with inert gas prior to cutting or welding existing lines.

Flammability Limits in Air

• Natural Gas (Methane): Lower Explosive Limit (LEL) = $5.0%$; Upper Explosive Limit (UEL) = $15.0%$
• Propane Gas: Lower Explosive Limit (LEL) = $2.1%$; Upper Explosive Limit (UEL) = $9.5%$

                               FLAMMABILITY RANGE MATRIX
   Natural Gas: [ 0% ── Safe ── 5% ══ EXPLOSIVE RANGE ══ 15% ── Too Rich ── 100% ]
   Propane Gas: [ 0% ── Safe ── 2.1% ═ EXPLOSIVE RANGE ═ 9.5% ── Too Rich ── 100% ]

Indoor vs. Outdoor Purge Location Limits

1. Indoor Purging: Permitted ONLY for small diameter pipes (less than $2\text{ inches}$ nominal size) and short piping runs (under $50\text{ feet}$). The space must be well-ventilated, free of open flames or electrical spark sources, and discharged through a burner orifice or hose.
2. Outdoor Purging Mandate: Piping 2 inches or larger in diameter, or piping runs exceeding 50 feet in length, MUST be purged directly to the outdoors. The outdoor purge line must terminate at least 10 feet ($3,048\text{ mm}$) away from building openings, mechanical air intakes, and potential ignition sources.
3. CGI Monitoring: Purging must continue until a calibrated Combustible Gas Indicator (CGI) confirms 100% fuel gas concentration at the discharge point.