8.1 Fuel Gas Piping Materials & Joints

Fuel Gas Piping Materials & Joints

1. Approved Fuel Gas Piping Materials & Code Specifications

Fuel gas distribution systems must be constructed using materials specifically approved by model codes, such as the International Fuel Gas Code (IFGC), National Fuel Gas Code (NFPA 54), and Uniform Plumbing Code (UPC Chapter 12). Gas piping materials must resist internal chemical exposure from gas constituents, structural soil loads, atmospheric corrosion, and mechanical stress.

┌────────────────────────────────────────────────────────────────────────────────────────┐
│                            APPROVED FUEL GAS PIPING MATERIALS                          │
├──────────────────────┬────────────────────────┬───────────────────┬────────────────────┤
│ Pipe Material        │ Code Standard          │ Approved Location │ Joining Methods    │
├──────────────────────┼────────────────────────┼───────────────────┼────────────────────┤
│ Black Steel          │ ASTM A53 / ASTM A106   │ Aboveground Int/Ext│ NPT Thread, Weld,  │
│                      │ Schedule 40            │                   │ Press-Fit (LC 4)   │
├──────────────────────┼────────────────────────┼───────────────────┼────────────────────┤
│ Corrugated Stainless │ ANSI LC 1 / CSA 6.26   │ Interior Chases &  │ Listed Mechanical  │
│ Steel Tubing (CSST)  │ Pre-jacketed Assembly  │ Walls (Aboveground│ Arc-Fittings Only  │
├──────────────────────┼────────────────────────┼───────────────────┼────────────────────┤
│ Copper & Brass       │ ASTM B88 (Types K & L) │ Interior / Ext    │ Brazed (BCuP),     │
│ Tubing               │ ASTM B280 (ACR)        │ (Max 0.3 gr H2S)  │ 45° SAE Flare      │
├──────────────────────┼────────────────────────┼───────────────────┼────────────────────┤
│ Polyethylene (PE)    │ ASTM D2513 SDR 11      │ Underground Ext   │ Heat Fusion,       │
│ Plastic              │ Yellow Pipe / Tubing   │ ONLY (No Buildings│ Category 1 Mech    │
└──────────────────────┴────────────────────────┴───────────────────┴────────────────────┘

Black Steel Pipe (Schedule 40)

Black steel pipe produced in accordance with ASTM A53 (Types E or S, Grade B) or ASTM A106 is the primary material used for interior aboveground gas distribution. It possesses high tensile strength and impact resistance. Malleable iron fittings (ASME B16.3) or wrought steel fittings (ASME B16.9) are required. Cast iron fittings and bushings are strictly prohibited due to their brittle nature, which makes them susceptible to cracking under mechanical tension or thermal expansion.

Corrugated Stainless Steel Tubing (CSST)

CSST is a flexible, thin-walled stainless steel pipe (typically 300-series alloy) protected by an outer yellow or black semi-rigid PVC jacket. Certified under ANSI LC 1 / CSA 6.26, CSST simplifies retrofits and long runs by reducing fitting count. However, CSST has specific code restrictions:

• Fitting Matching: CSST must be installed using only the proprietary mechanical fittings manufactured by the specific CSST system vendor. Interchanging fittings between different manufacturers (e.g., Gastite, TracPipe, Wardflex) voids listing approvals and is a major code violation.
• Electrical Bonding Mandate: Non-arc-resistant CSST systems must be bonded to the electrical grounding electrode system using a copper conductor not smaller than 6 AWG. The bonding clamp must attach to a rigid metallic pipe fitting or brass manifold adjacent to the building gas service entry or gas meter. This bonding safely dissipates high-voltage electrical energy induced by indirect lightning strikes, which could otherwise puncture the thin stainless steel tubing wall and ignite gas.
• Arc-Resistant CSST: Systems utilizing arc-resistant black jackets (complying with ANSI LC 1027) reduce or eliminate the 6 AWG bonding requirement in some local jurisdictions, but must still be installed per manufacturer listings.

Copper and Brass Tubing

Copper tubing (ASTM B88 Types K and L, or ASTM B280) is permitted for natural gas and liquefied petroleum (LP) gas, subject to a critical chemical restriction:

$\text{Hydrogen Sulfide Limit} \le 0.3 \text{ grains } H_2S \text{ per } 100 \text{ standard cubic feet of gas } (0.7 \text{ mg}/100 \text{ L})$

If natural gas contains higher concentrations of hydrogen sulfide ($H_2S$), it reacts chemically with copper to produce copper sulfide flakes. These internal flakes flake off the pipe wall, travel downstream, and clog appliance orifices, pilot tubes, and safety shutoff valves. Where copper is permitted, joints must be brazed using filler metals containing a melting point above $1,000^\circ\text{F}$ ($538^\circ\text{C}$) (such as AWS BCuP series) or joined using listed $45^\circ$ SAE flare fittings. Soft-soldered joints ($50/50$ or $95/5$ lead-free) are strictly prohibited for fuel gas piping.

Polyethylene (PE) Plastic Pipe

Polyethylene pipe (ASTM D2513, typically yellow SDR 11) is used extensively for natural gas main distribution and service lines. Its installation is governed by strict code boundaries:

1. Underground Exterior Use Only: PE pipe must be installed strictly underground outside the building footprint. It is forbidden to run PE pipe aboveground, inside a building, or underneath a building slab.
2. Burial Depth: PE gas pipe must be buried with a minimum earth cover of 18 inches ($457\text{ mm}$) in normal soil, and a minimum of 24 inches ($610\text{ mm}$) where subject to vehicular traffic (such as driveways and parking lots).
3. Tracer Wire Requirement: Because plastic pipe is non-conductive and cannot be detected by electromagnetic pipe locators, an insulated, continuous copper tracer wire (minimum 18 AWG yellow jacketed) or tape must be buried alongside the PE pipe. One end of the tracer wire must extend aboveground at a riser or curb valve box to allow utility locating.
4. Anodeless Risers: The transition from underground PE pipe to aboveground metallic piping entering a building must be made using a factory-assembled anodeless riser. The anodeless riser protects the PE pipe inside a rigid steel casing and prevents soil settlement shear forces from cracking the plastic transition joint.

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2. Fittings, Valve Requirements, & Joining Methods

Threaded Joints

Tapered pipe threads must comply with ASME B1.20.1 (NPT), possessing a standard 1:16 thread taper ratio. Pipe joint compound (pipe dope) or yellow PTFE thread sealant tape certified for fuel gas must be applied exclusively to the male threads.

Critical Installation Rule: The first two male starter threads must be left completely bare of dope or tape. This prevents excess sealant from being sheared off into the interior of the pipe during joint makeup, where it could travel downstream and plug gas valves or burner orifices.

Welded and Flanged Joints

Welded piping is mandatory for gas pressures exceeding $5\text{ psi}$ ($34.5\text{ kPa}$) in commercial/industrial buildings, and for pipe diameters exceeding $4\text{ inches}$ ($100\text{ mm}$). Welding must be performed by certified welders in accordance with ASME Boiler and Pressure Vessel Code, Section IX. Flanged joints must use ASME B16.5 steel flanges with full-face gas-rated gaskets (such as non-asbestos synthetic rubber or spiral-wound metal).

Press-Connect Fittings

Mechanically pressed fittings for Schedule 40 black steel pipe (e.g., Viega MegaPress) must be tested and listed to ANSI LC 4 / CSA 6.32. These fittings incorporate a internal HNBR (Hydrogenated Nitrile Butadiene Rubber) yellow sealing O-ring and a stainless steel grip ring, pressed using calibrated hydraulic crimping tools.

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3. Dielectric Unions & Galvanic Isolation

When dissimilar metals (such as copper and steel) are directly joined in a fuel gas system in the presence of atmospheric moisture, an electrochemical cell is established. The metal with the higher galvanic potential (steel) acts as an anode and corrodes rapidly.

To prevent galvanic failure, dielectric unions, dielectric flange kits, or brass transition fittings must be installed at all copper-to-steel connections. Furthermore, underground metallic gas pipes must be factory-coated with polyethylene tape/epoxy or protected with sacrificial anodes (cathodic protection) to prevent aggressive soil electrolysis.

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4. Protection of Concealed Gas Piping & Striker Plates

Where gas piping is installed through wood wall studs, floor joists, or top/bottom plates within 1.5 inches ($38\text{ mm}$) of the framing edge, the pipe must be protected from nail or screw penetration.

               WOOD STUD FRAMING PENETRATION
      ┌──────────────────────────────────────────────┐
      │                                              │
      │     ┌──────────────────────────────────┐     │
      │     │ 16-Gauge Hardened Steel Plate    │     │
      │     │ (Must extend min 2 in. beyond)   │     │
      │     └──────────────────────────────────┘     │
      │           ○ Gas Pipe Penetration             │
      │    (If clearance to edge is < 1.5 in.)       │
      │                                              │
      └──────────────────────────────────────────────┘

Shielding requires 1/16-inch thick (16-gauge) hardened steel striker plates. Striker plates must cover the area of the pipe penetration and extend at least 2 inches ($51\text{ mm}$) beyond the outer edges of adjacent structural members.