10.3 Fuel Gas Piping Materials, Sizing & Pressure Testing (IFGC Chapter 4)

10.3 Fuel Gas Piping Materials, Sizing & Pressure Testing (IFGC Chapter 4)

[!NOTE] Statutory Code Authority: Fuel gas distribution infrastructure in Arkansas is regulated by the 2021 International Fuel Gas Code (IFGC Chapter 4), the Arkansas Plumbing & Fuel Gas Code, and NFPA 54 (National Fuel Gas Code). Contractors installing natural gas ($CH_4$) or liquefied petroleum ($LP$/propane, $C_3H_8$) piping systems are legally responsible for material compliance, strike protection, bonding, hydraulic sizing tables, rigorous non-destructive pressure testing, and sediment trap geometry.

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Approved Fuel Gas Piping Materials & Limitations

Under 2021 IFGC Section 403, piping materials installed inside or outside buildings must comply with stringent ASTM and ANSI material specifications.

                               APPROVED FUEL GAS PIPING MATERIALS
                               
  +─────────────────────────────────────────────────────────────────────────────────────────+
  │ Schedule 40 Black Steel (ASTM A53 / A106)                                               │
  │ - Threaded with Malleable Iron Fittings (ASME B16.3)                                    │
  │ - Approved indoors and outdoors; the commercial gold standard                           │
  +─────────────────────────────────────────────────────────────────────────────────────────+
  │ Corrugated Stainless Steel Tubing - CSST (ANSI LC 1 / CSA 6.26)                         │
  │ - Semi-rigid flexible tubing; eliminates 75% of threaded joints                         │
  │ - MANDATORY: 6 AWG Direct Electrical Bonding & Hardened Striker Plates                  │
  +─────────────────────────────────────────────────────────────────────────────────────────+
  │ Copper & Brass Tubing (ASTM B88 Type K/L; ASTM B280 ACR)                                │
  │ - Joints brazed with BCuP filler (> 1,000°F melting point; no soft solder)              │
  │ - STRICT LIMITATION: Banned if gas has > 0.3 grains H2S per 100 scf (natural gas ban)   │
  +─────────────────────────────────────────────────────────────────────────────────────────+
  │ Polyethylene - PE Plastic (ASTM D2513)                                                  │
  │ - Heat-fusion or mechanical fittings; strictly OUTDOORS UNDERGROUND ONLY                │
  │ - Banned inside buildings; requires 18 AWG yellow tracer wire & anodeless riser         │
  +─────────────────────────────────────────────────────────────────────────────────────────+

1. Schedule 40 Black Iron & Steel Pipe

• Specifications: ASTM A53 (Types E, S, or F) or ASTM A106 seamless carbon steel. Threaded fittings must be malleable iron or ductile iron rated for at least 150 psig (ASME B16.3). Cast iron fittings are strictly prohibited.
• Galvanized Steel Code Reality: Contrary to an obsolete trade myth, galvanized steel pipe is legally permitted by IFGC Section 403.4.2. However, black steel remains the universal industry standard because older gas manufacturing techniques produced chemical reactions that flaked zinc galvanizing; today's dry natural gas does not react with zinc, but black steel is universally stocked and preferred.
• Pipe Joint Compounds: Pipe thread sealant (pipe dope) or PTFE thread tape (certified yellow gas tape) must be applied exclusively to male external pipe threads. The first two threads at the tip must be left clean and bare to prevent excess paste from shearing off and entering internal gas valve pilot orifices or regulator seats.

2. Corrugated Stainless Steel Tubing (CSST)

• Standard: ANSI LC 1 / CSA 6.26. CSST consists of thin-walled, corrugated 304 stainless steel tubing jacketed in yellow polyethylene or black conductive arc-resistant polymer.
• Direct Electrical Bonding Mandate (IFGC Section 310.2 & NFPA 54): Standard yellow-jacketed CSST is susceptible to perforation from indirect lightning strikes. Lightning striking near a building induces high electrical potential on metallic piping; the charge arcs from the thin CSST wall to adjacent grounded metal (electrical conduits, HVAC ducts, framing), vaporizing a pinhole in the stainless steel and igniting high-pressure gas. To prevent arcing:
  1. CSST systems must be bonded to the electrical service grounding electrode system using a minimum 6 AWG copper bonding conductor.
  2. The bonding clamp must be attached to an approved brass CSST fitting, rigid pipe manifold, or black iron pipe segment located upstream of the CSST run.
  3. Black-jacketed arc-resistant CSST (certified to ANSI LC 1027) incorporates an internal conductive layer that dissipates lightning energy, often eliminating the requirement for a separate 6 AWG bonding jumper under manufacturer listing instructions.
• Mechanical Protection (Striker Plates - IFGC Section 404.7): Where CSST or copper tubing passes through structural wall studs, floor plates, or roof rafters closer than 1.5 inches (38 mm) from the framing edge, it must be protected against puncture from drywall screws and nails. Contractors must install hardened steel striker plates (tested to ANSI LC 1 standards) having a minimum thickness of 0.0508 inches (1.3 mm - No. 16 gauge) extending at least 4 inches beyond structural members.

3. Copper and Brass Tubing Restrictions (IFGC Section 403.4.3)

• Copper tubing (ASTM B88 Type K or L) and brass pipe are approved in principle for fuel gas, provided joints are brazed using filler metal with a melting point exceeding 1,000°F (538°C) (such as BCuP-5 phosphorus-copper-silver alloy). Soft soldered (50/50, 95/5) joints are strictly prohibited.
• CRITICAL RESTRICTION: Under IFGC Section 403.4.3, copper tubing shall NOT be utilized if the fuel gas contains more than 0.3 grains of hydrogen sulfide ($H_2S$) per 100 standard cubic feet of gas ($4.9\text{ mg/100 m}^3$).
• Chemical Mechanism: Hydrogen sulfide reacts chemically with bare copper to form copper sulfide ($Cu_2S$ and $CuS$). This compound forms flaky black scale that sloughs off the interior pipe wall, traveling downstream to foul regulator seats, pilot orifices, and combination gas valves. Because most natural gas utilities allow odorants and trace $H_2S$ exceeding this threshold, copper tubing is widely prohibited for natural gas installations across utility jurisdictions, while remaining code-compliant for clean Liquefied Petroleum (LP/propane) gas.

4. Polyethylene Plastic Pipe (PE)

• Standard: ASTM D2513. High-density polyethylene (HDPE) or medium-density polyethylene (MDPE).
• Underground Outdoor Restriction Only: Plastic gas pipe is strictly prohibited above ground and inside any building structure. It must be installed underground with a minimum burial depth of 18 inches (457 mm) (or 12 inches if approved by the code official and not subject to external vehicular damage).
• Tracer Wire Mandate: Under IFGC Section 404.17.3, all underground nonmetallic piping must be installed with an insulated, yellow-jacketed copper tracer wire not smaller than 18 AWG. The tracer wire must be taped to the pipe, terminate above ground at each end with access for electronic locating transmitters, and never contact the gas flow.
• Transition to Building: Underground plastic pipe must transition to metallic pipe prior to emerging above ground using a factory-assembled anodeless riser with an internal Schedule 40 steel casing.

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Fuel Gas Pipe Sizing Methodologies

Fuel gas piping must deliver adequate volumetric flow to all appliances firing simultaneously at full rated capacity while maintaining minimum required operational pressure. Sizing is governed by the specific gravity of the gas, allowable pressure drop, and developed pipe length.

Fundamental Gas Physical Parameters

• Natural Gas: Specific gravity $SG = 0.60$ (lighter than air, $1.00$). Nominal heating value $= 1,000\text{ to }1,050\text{ BTU/ft}^3$ (standard sizing uses $1,000\text{ BTU} = 1.0\text{ cubic foot}$).
• LP / Propane Gas: Specific gravity $SG = 1.50\text{ to }1.52$ (heavier than air; settles in low basements/crawlspaces). Nominal heating value $= 2,500\text{ BTU/ft}^3$ (standard sizing uses $2,500\text{ BTU} = 1.0\text{ cubic foot}$).

Low-Pressure Sizing Criteria

For standard low-pressure systems with a nominal utility delivery pressure of 7.0 inches water column (in. w.c.) ($\approx 0.25\text{ psig}$), the maximum allowable design pressure drop from the meter to the furthest appliance is 0.5 inches water column (0.018 psi). Sizing is executed using IFGC Table 402.4(1) (Schedule 40 Metallic Pipe, Natural Gas, 0.5 in. w.c. drop) or Table 402.4(14) for CSST.

The Longest Length Method (IFGC Section 402.4.1)

This is the primary prescriptive sizing method mandated on licensing exams:

1. Step 1: Determine Longest Developed Length: Measure the total linear distance from the gas meter (or regulator) to the single most remote appliance in the piping layout, adding equivalent lengths for fittings.
2. Step 2: Select the Sizing Column: In the appropriate IFGC table, locate the column corresponding to this longest developed length. This single column will be used to size every section of the piping network!
3. Step 3: Size the Main Trunk Lines: For each main piping section, calculate the total combined gas demand (CFH = total BTU/hr divided by 1,000) of all appliances served downstream of that section. Look down the longest length column to select the minimum pipe diameter that equals or exceeds this demand.
4. Step 4: Size Individual Branch Lines: For each branch line leading directly to an appliance, look down the same longest length column and select the pipe diameter capable of delivering that specific appliance's demand.

[!WARNING] Common Sizing Pitfall: Never size branch lines using their actual shorter branch lengths! If a furnace is 80 feet away and a water heater is 20 feet away, sizing the water heater branch from the "20 ft column" would underestimate the cumulative friction through the common trunk, causing pressure to drop below minimum operating limits when both appliances fire simultaneously.

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Mandatory Pressure Testing Procedures (IFGC Section 406)

Before any fuel gas piping is concealed, drywalled, or connected to appliances, it must undergo rigorous hydrostatic or pneumatic pressure testing witnessed and approved by the mechanical code inspector.

                               GAS PIPING PRESSURE TEST PROTOCOL
                               
        [Test Block / Manometer Gauge]
                     │
                     ▼
     ══════════════════════════════════════ [PIPING SYSTEM] ═══════════════
                     ▲                                            ▲
                     │                                            │
       [Air / Nitrogen Pressurization]               [Appliances ISOLATED & CAPPED]
       - Residential: >= 3.0 psig / 10 min           - Never test against appliance valves!
       - Commercial: >= 10.0 psig / 30 min           - Diaphragms rupture > 0.5 psig

1. Test Pressure & Duration Mandates

• Residential Systems (One- and Two-Family Dwellings - IFGC 406.4.1):
  • The test pressure must be not less than 1.5 times the maximum working pressure, but in no case less than 3.0 psig (20 kPa) or 10 feet of water column.
  • Test Duration: Minimum 10 minutes with zero detectable pressure drop on the test gauge.
• Commercial / High-Pressure Systems (IFGC 406.4.2):
  • For commercial installations, multi-family buildings, or piping designed for pressures exceeding 0.5 psig, the test pressure must be not less than 10.0 psig (69 kPa).
  • Test Duration: Minimum 30 minutes for each 500 cubic feet ($14.2\text{ m}^3$) of pipe volume or fraction thereof.

2. Test Media & Prohibited Gases

• Testing must be conducted using clean air, nitrogen, carbon dioxide ($CO_2$), or an approved inert gas.
• STRICT PROHIBITION: OXYGEN MUST NEVER BE USED FOR PRESSURE TESTING UNDER ANY CIRCUMSTANCES. Pure oxygen mixed with residual pipe-threading cutting oils or trace hydrocarbons creates an immediate, violent explosion hazard.

3. Test Gauge Calibration Standards (IFGC Section 406.4)

• The test gauge must have a calibrated dial scale such that the test pressure falls within the middle half of the gauge scale.
• For a 3.0 psig residential test, the contractor must use a gauge with a maximum scale of 0 to 6 psig or 0 to 15 psig, calibrated in increments of 0.1 or 0.2 psi (or a certified digital manometer). Using a standard 0 to 100 psig gauge to perform a 3 psig test is an automatic code failure because a 0.2 psi leak cannot be visually resolved on a 100 psi dial.

4. Isolation of Sensitive Appliances & Regulators

• Standard combination gas valves on appliances and appliance line regulators are engineered for a maximum working pressure of 0.5 psig (14 inches water column).
• Testing piping at 3 psig to 10 psig directly against an appliance gas valve will rupture the valve's rubber diaphragm and blow out safety seals. During the test, every appliance must be completely disconnected and capped with a threaded black iron plug, or isolated with an approved shutoff valve rated for the test pressure.

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Appliance Shutoff Valves & Sediment Traps

1. Appliance Shutoff Valve Standards (IFGC Section 409)

• Every fuel gas appliance must have an individual, accessible manual shutoff valve installed upstream of the appliance.
• Location Mandate: The shutoff valve must be located in the same room as the appliance, within 6 feet (1,829 mm) of the appliance inlet, and upstream of the union or flexible appliance connector.
• Valve Specifications: Must be a listed, quarter-turn full-port ball valve bearing the CSA / AGA stamp.

2. Sediment Traps (Drip Legs - IFGC Section 408)

• Purpose: Fuel gas carries minute particles of rust, steel mill scale, pipe dope shavings, and liquid hydrocarbon condensates. If these debris enter the combination gas valve, they lodge in the valve seat, preventing complete shutoff or clogging the 3.5" w.c. regulator.
• Geometry & Placement:
  • Must be installed downstream of the appliance manual shutoff valve and as close to the appliance inlet as practical.
  • Constructed using a tee fitting with a capped nipple not less than 3 inches (76 mm) in length extending vertically downward from the bottom outlet of the tee.
  • The 90-Degree Turn Mandate: Gas flow from the supply line must enter the run of the tee and make a sharp 90-degree turn out the side branch into the appliance. As the gas changes direction, heavy solid contaminants and liquid droplets continue downward via momentum and gravity into the dead-end capped nipple.
  • Code Exemptions: Under IFGC Section 408.4, sediment traps are not required for illuminating appliances, gas ranges, clothes dryers, outdoor grills, and decorative vented gas fireplaces.