10.3 Fuel Gas Piping Installation: Materials, Sizing Tables & Pressure Testing

Fuel Gas Piping: Materials, Sizing & Safety Protocols

Fuel gas piping systems conveying Natural Gas (methane, $\text{CH}_4$) or Liquefied Petroleum Gas (propane, $\text{C}_3\text{H}_8$) are subject to stringent mechanical standards under the International Fuel Gas Code (IFGC) and NFPA 54 (National Fuel Gas Code). Because fuel gases possess high flammability and explosive potential, improper material selection, undersized piping, missing sediment traps, or inadequate bonding can result in catastrophic structural fires, gas explosions, or carbon monoxide poisoning.

Contractors in Arizona must understand approved gas piping materials, direct electrical bonding requirements for Corrugated Stainless Steel Tubing (CSST), underground burial standards, pipe sizing using the IFGC Longest Length Method, and pneumatic pressure testing procedures.

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1. Fuel Gas Piping Materials & Installation Mandates

+---------------------------------------------------------------------------------------------------+
|                         IFGC APPROVED FUEL GAS PIPING MATERIALS                                   |
+---------------------------------------------------------------------------------------------------+
|  MATERIAL TYPE              | CODE SPECIFICATION                | APPROVED LOCATIONS & LIMITATIONS|
+-----------------------------+-----------------------------------+---------------------------------+
|  Schedule 40 Black Steel    | ASTM A53 / ASTM A106 Threaded     | Indoors & Outdoors; Malleable   |
|                             | Fittings (ASME B16.3 Class 150)   | iron fittings; Thread sealant   |
|                             |                                   |                                 |
|  Corrugated Stainless Steel | ASTM A240 / ANSI LC 1             | Indoors only; Direct 6 AWG      |
|  Tubing (CSST)              | 300-Series Stainless Steel        | bonding jumper mandatory        |
|                             |                                   |                                 |
|  Polyethylene (PE) Plastic  | ASTM D2513 SDR-11 Pipe            | OUTDOORS UNDERGROUND ONLY;      |
|                             | Heat fusion or mechanical joints  | Prohibited inside or under slab |
|                             |                                   |                                 |
|  Copper & Brass Tubing      | ASTM B88 Type L / ASTM B280       | ONLY permitted where gas has    |
|                             | Brazed with BCuP or BAg alloys    | < 0.3 grains H2S per 100 cu ft  |
+-----------------------------+-----------------------------------+---------------------------------+

1. Schedule 40 Black Iron (Carbon Steel) Pipe

Black steel pipe is the traditional standard for interior gas distribution. Threaded joints must be cut with clean National Pipe Taper (NPT) threads ($3/4\text{ inch}$ taper per foot). Pipe joint compound (pipe dope) or gas-rated yellow PTFE tape must be applied strictly to the male threads only, leaving the first two leading threads bare to prevent sealant from washing into gas regulator orifices and valve seats.

2. Corrugated Stainless Steel Tubing (CSST) & Direct Bonding

CSST consists of a flexible, semi-rigid corrugated 300-series stainless steel core covered by a yellow or black protective polyethylene jacket. While CSST dramatically reduces installation labor, its thin stainless steel wall ($0.010\text{ to }0.015\text{ inches}$) is highly vulnerable to perforation from indirect lightning strikes.

                               CSST DIRECT ELECTRICAL BONDING SYSTEM
    
          Gas Meter / Regulator ────► CSST Brass Fitting / Manifold
                                               │
                                               ▼ (Listed Grounding Clamp)
                                               │
                                               │ Minimum 6 AWG Bare / Green Copper Wire
                                               │ (Keep run as short and straight as possible)
                                               ▼
                                Electrical Service Equipment Enclosure
                                 or Building Grounding Electrode System

• Mandatory Bonding Rule (IFGC Section 310, "Electrical Bonding and Grounding" — CSST is addressed at 310.1.1 in the 2018 edition): CSST gas piping systems that are not listed with an arc-resistant jacket must be electrically continuous and bonded to the building electrical service grounding electrode system.
• Bonding Conductor: The bonding jumper must be a minimum 6 AWG solid or stranded copper wire, secured to a listed brass CSST fitting or steel manifold using an approved pipe grounding clamp.
• Arcing Prevention: This direct bond equalizes electrical potential during nearby lightning strikes, preventing electrical energy from arcing between the CSST tubing and nearby grounded metal pipes or HVAC ducts.
• Striker Plates: Where CSST passes through wall studs, floor joists, or framing members within $3\text{ inches}$ of the framing edge, hardened steel striker plates (minimum $0.0575\text{ inch}$ thick, No. 16 gauge) must be installed to prevent puncture by drywall screws or nails.

3. Underground Polyethylene (PE) Gas Piping (IFGC 404.14)

• Outdoor Underground Limitation: PE pipe (ASTM D2513) is approved strictly for outdoor, underground burial. It is strictly prohibited from entering a building, being installed inside walls, or being routed under a concrete slab foundation unless fully encased in a gas-tight, vented steel sleeve conduit.
• Burial Depth: Underground gas piping must be buried with a minimum earth cover of $12\text{ inches}$ in private residential locations, and $18\text{ inches}$ where subject to external surface damage (under driveways, parking lots, or roadways).
• Tracer Wire Requirement: Because plastic pipe is non-conductive and invisible to electronic pipe locators, an 18 AWG yellow insulated copper tracer wire (or metallized warning tape) must be buried continuously alongside the PE pipe. The tracer wire must terminate aboveground at each end with access for transmitter connection.
• Anodeless Transition Risers: PE pipe must never terminate above ground where exposed to UV sunlight or mechanical damage. The transition from underground PE to aboveground steel piping must be made using a factory-assembled anodeless transition riser with an internal gas seal and fusion joint.

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2. Gas Piping Sizing Methodology: The Longest Length Method

To ensure all gas appliances receive adequate fuel volume during simultaneous full-load operation, piping must be sized in accordance with IFGC Chapter 4 sizing tables based on an allowable pressure drop of $0.5\text{ in. w.c.}$ for low-pressure systems ($<0.5\text{ psig}$ / $7\text{--}14\text{ in. w.c.}$). Sizing gas piping solely based on nominal pipe diameter without calculating equivalent lengths and load capacity is a dangerous field error.

+---------------------------------------------------------------------------------------------------+
|                             FUEL GAS THERMAL CONSTANTS & DENSITIES                                |
+---------------------------------------------------------------------------------------------------+
|  FUEL GAS TYPE              | HEATING VALUE (HHV)               | SPECIFIC GRAVITY (AIR = 1.00)   |
+-----------------------------+-----------------------------------+---------------------------------+
|  Natural Gas (Methane, CH4) | ~1,000 BTU / Cubic Foot (CFH)     | 0.60 (Lighter than air; rises)  |
|  Propane (LP Gas, C3H8)     | ~2,500 BTU / Cubic Foot (CFH)     | 1.50 (Heavier than air; sinks)  |
+-----------------------------+-----------------------------------+---------------------------------+

Volumetric Load Conversion (CFH)

$\text{Natural Gas Demand (CFH)} = \frac{\text{Appliance Input Rating (BTU/hr)}}{1,000\text{ BTU/cu ft}}$

$\text{Propane LP Demand (CFH)} = \frac{\text{Appliance Input Rating (BTU/hr)}}{2,500\text{ BTU/cu ft}}$

The Step-by-Step Longest Length Method (IFGC 402.4)

1. Step 1: Determine the Longest Length ($L_{\text{max}}$): Measure the total physical distance along the pipe run from the gas meter outlet (or LP second-stage regulator) to the most remote appliance outlet in the building. This single maximum length is used to select the capacity column for ALL pipe segments in the entire system.
2. Step 2: Calculate Segment Loads: Determine the total gas demand in Cubic Feet per Hour ($\text{CFH}$) carried by each pipe section:
   • Main Trunk: Carries the sum of all downstream appliances.
   • Branch Lines: Carry only the demand of the specific appliance(s) served by that branch.
3. Step 3: Select Pipe Diameters: In the IFGC Sizing Table (e.g., Table 402.4(1) for Schedule 40 Black Iron, $0.5\text{ in. w.c.}$ drop, $0.60$ specific gravity):
   • Locate the column header matching or exceeding the Longest Length ($L_{\text{max}}$).
   • For each pipe segment, read down the selected column until finding a capacity equal to or greater than that segment's required $\text{CFH}$. Read across to determine the required nominal pipe diameter.

+---------------------------------------------------------------------------------------------------+
|                 SAMPLE IFGC SIZING TABLE: SCH 40 BLACK IRON (0.5 in. w.c. DROP, 0.60 SG)          |
+---------------------------------------------------------------------------------------------------+
|  NOMINAL PIPE SIZE (INCHES) | 10 FT LENGTH    | 20 FT LENGTH    | 40 FT LENGTH    | 60 FT LENGTH  |
+-----------------------------+-----------------+-----------------+-----------------+---------------+
|  1/2 in.                    | 172 CFH         | 118 CFH         | 81 CFH          | 65 CFH        |
|  3/4 in.                    | 360 CFH         | 247 CFH         | 170 CFH         | 137 CFH       |
|  1 in.                      | 678 CFH         | 466 CFH         | 320 CFH         | 257 CFH       |
|  1-1/4 in.                  | 1,390 CFH       | 957 CFH         | 657 CFH         | 528 CFH       |
|  1-1/2 in.                  | 2,090 CFH       | 1,430 CFH       | 985 CFH         | 791 CFH       |
+-----------------------------+-----------------+-----------------+-----------------+---------------+

Worked Engineering Problem: Gas Piping Sizing

Scenario: A residential installation in Phoenix requires natural gas piping for three appliances:

• Gas Furnace: $100,000\text{ BTU/hr} = 100\text{ CFH}$
• Tankless Water Heater: $199,000\text{ BTU/hr} = 199\text{ CFH}$
• Gas Range / Cooktop: $65,000\text{ BTU/hr} = 65\text{ CFH}$

Distances from Meter:

• Meter to Main Split Tee: $20\text{ ft}$
• Split Tee to Furnace: $15\text{ ft}$ (Total from meter = $35\text{ ft}$)
• Split Tee to Water Heater: $10\text{ ft}$ (Total from meter = $30\text{ ft}$)
• Split Tee to Gas Range: $40\text{ ft}$ (Total from meter = $60\text{ ft}$)

Step 1: Identify Longest Length: The most remote appliance is the Gas Range at $60\text{ feet}$. Therefore, the $60\text{ ft}$ column must be used to size every segment.

Step 2: Size Each Segment (all read from the $60\text{ ft}$ column):

• Main Trunk (Meter to Split Tee):
  • Carries all 3 appliances: $100 + 199 + 65 = 364\text{ CFH}$.
  • In the $60\text{ ft}$ column, $1\text{ in.}$ handles only $257\text{ CFH}$ — not enough. $1\text{-}1/4\text{ in.}$ handles $528\text{ CFH} \ge 364\text{ CFH}$. $\rightarrow$ Select $1\text{-}1/4\text{ inch}$ Pipe.
• Furnace Branch ($100\text{ CFH}$):
  • $1/2\text{ in.}$ handles $65\text{ CFH}$ (too small); $3/4\text{ in.}$ handles $137\text{ CFH}$. $\rightarrow$ Select $3/4\text{ inch}$ Pipe.
• Water Heater Branch ($199\text{ CFH}$):
  • $3/4\text{ in.}$ handles $137\text{ CFH}$ (too small); $1\text{ in.}$ handles $257\text{ CFH}$. $\rightarrow$ Select $1\text{ inch}$ Pipe.
• Range Branch ($65\text{ CFH}$):
  • $1/2\text{ in.}$ handles exactly $65\text{ CFH}$. $\rightarrow$ Select $1/2\text{ inch}$ Pipe (sized to capacity with no margin — many designers step up to $3/4\text{ in.}$).

[!WARNING] The single most common sizing error is reading the wrong length column. Capacity falls steeply with length: $1\text{ in.}$ Schedule 40 carries $678\text{ CFH}$ at $10\text{ ft}$ but only $257\text{ CFH}$ at $60\text{ ft}$. Using the branch's own short run instead of the system's longest length undersizes the trunk by a full pipe size or more.

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3. Appliance Connections: Shutoff Valves & Sediment Traps

                              IFGC APPLIANCE GAS CONNECTION GEOMETRY
    
          Gas Supply Piping Main
                   │
                   ▼
          ┌─────────────────┐
          │  Manual Shutoff │ ◄─── Listed Shutoff Valve within 6 ft in Same Room
          │      Valve      │
          └────────┬────────┘
                   │
          ┌────────┴────────┐
          │ Flexible Metal  │ ◄─── ANSI Z21.24 Connector (Max 6 ft overall, one only)
          │    Connector    │      (No wall/floor/cabinet penetrations)
          └────────┬────────┘
                   │
                   ▼  Gas Flow (Changes Direction 90° into Appliance)
              ┌────┴────┐
              │ Tee     │────────────────► To Appliance Gas Control Valve
              └────┬────┘
                   │
                   │ ◄─── Capped Nipple, Vertical (2018 IFGC: any length)
                   │
              ┌────┴────┐
              │ Pipe Cap│ ◄─── Sediment Trap (Dirt Leg)
              └─────────┘      (Traps heavy scale, dirt, and moisture droplets)

• Manual Shutoff Valve (IFGC 409.5): Each gas appliance must be provided with an individual listed shutoff valve located in the same room as the appliance, within $6\text{ feet}$ ($1,829\text{ mm}$) of the appliance inlet, installed upstream of the union and flexible connector.
• Sediment Trap / Dirt Leg (IFGC 408.4): Where a sediment trap is not built into the appliance, one must be installed downstream of the appliance shutoff valve, as close to the appliance inlet as practical. The 2018 IFGC requires "a tee fitting having a capped nipple of any length installed vertically in the bottommost opening of the tee" — the older "not less than 3 inches" wording was dropped from the model code, though some jurisdictions amend it back in, so verify the locally adopted edition. Gas enters the top of the tee and makes a $90^\circ$ direction change out the side branch, dropping heavy pipe scale, rust and moisture into the capped nipple before it reaches the gas valve. Illuminating appliances, ranges, clothes dryers, decorative vented appliances, gas fireplaces and outdoor grills are exempt.
• Flexible Gas Connectors (IFGC 411.1.3.1): Corrugated metal appliance connectors (ANSI Z21.24) must have an overall length not exceeding $6\text{ feet}$, measured along the centerline, and only one connector may be used per appliance. Rigid metallic piping may exceed 6 feet if it is sized as part of the piping system under Section 402 and the shutoff valve complies with Section 409.5. Connectors are prohibited from passing through walls, floors, partitions, ceilings or appliance housings.

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4. Mandatory Pneumatic Pressure Testing (IFGC Section 406)

Before any new gas piping system is put into service or concealed inside walls, it must undergo a rigorous pressure test witnessed by the local building code official.

+---------------------------------------------------------------------------------------------------+
|                         IFGC SECTION 406 PRESSURE TESTING SPECIFICATIONS                          |
+---------------------------------------------------------------------------------------------------+
|  TEST PARAMETER             | CODE MANDATE                      | CRITICAL SAFETY RULE            |
+-----------------------------+-----------------------------------+---------------------------------+
|  Test Medium                | Air, Nitrogen, or Carbon Dioxide  | NEVER USE OXYGEN (EXPLOSION RISK|
|  Appliance Isolation        | All appliances MUST be disconnected| Test pressure destroys appliance|
|                             | or valves capped off              | control valves (rated 0.5 psig) |
|  Minimum Test Pressure      | ≥ 1.5× Working Pressure           | Standard field test is          |
|                             | AND NOT LESS THAN 3.0 psig        | 10.0 to 15.0 psig               |
|  Minimum Test Duration      | 10 minutes (Residential)          | 30 to 60+ min (Commercial)      |
|  Test Pressure Gauge        | Diaphragm / Spring Gauge          | Test pressure must fall within  |
|                             | Max scale: 5x test pressure       | middle 50% of gauge face        |
|  Leak Detection Method      | ASTM E515 Approved Bubble Solution| NEVER USE AN OPEN FLAME/MATCH   |
|                             | or electronic combustible sniffer | Soap bubbles must not corrode   |
+-----------------------------+-----------------------------------+---------------------------------+

Testing Procedure

1. Isolate Appliances: Disconnect all appliance flexible connectors and plug or cap the appliance isolation valves. Gas control valves on furnaces and water heaters are rated for a maximum pressure of $0.5\text{ psig}$ ($14\text{ in. w.c.}$); subjecting them to $10\text{--}15\text{ psig}$ will rupture the internal rubber diaphragms.
2. Pressurize: Pressurize the piping system with air or dry nitrogen to $10\text{ to }15\text{ psig}$ (minimum code requirement is $1.5\times$ working pressure or $3.0\text{ psig}$, whichever is greater).
3. Monitor Pressure: Monitor the pressure gauge for at least $10\text{ to }15\text{ minutes}$. There must be zero measurable pressure drop during the test period (accounting for temperature stabilization).
4. Leak Location: If pressure drops, apply an approved non-corrosive bubble solution conforming to ASTM E515 to all joints, fittings, and seams. Never use an open flame or match to search for gas leaks.