14.2 Fuel Gas Piping Materials, Fittings, Joining & Hangers

14.2 Fuel Gas Piping Materials, Fittings, Joining & Hangers

Exam Focus: Material specifications, joining standards, structural support intervals, and electrical safety bonding constitute core regulatory requirements on the Michigan Journeyman Plumber licensing exam. Candidates must master International Fuel Gas Code (IFGC) Section 403 (Piping Materials), Section 404 (Piping System Installation), Section 310 (Electrical Bonding of CSST), and Table 415.1 (Hanger Spacing). Knowing the precise restrictions on underground plastic piping, the threshold for copper tubing sulfide degradation, prohibited threaded fittings, and bonding clamp sizing is critical for both the written exam and jobsite compliance.

Scope note - where fuel gas sits in Michigan. Fuel gas piping is not governed by the Michigan Plumbing Code. Michigan's amended MPC 101.2 (R 408.30711) states that "the design and installation of gas piping ... shall conform to the Michigan mechanical code," and the Michigan Mechanical Code in turn assigns fuel gas distribution piping, fuel gas-fired appliances and their venting systems to the International Fuel Gas Code; one- and two-family dwellings follow Chapter 24 of the Michigan Residential Code. The three references PSI lists for the Journey Plumber written examination are the 2021 Michigan Plumbing Code, the State Construction Code Act (1972 PA 230), and the Skilled Trades Regulation Act (2016 PA 407) - no fuel gas code. Treat this chapter as supporting trade knowledge that you will need on the job and that may appear in general plumbing-practice questions, not as Michigan Plumbing Code content you can look up during the open-book exam.

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1. Approved Fuel Gas Piping Materials (IFGC Section 403)

Fuel gas piping must withstand internal pneumatic pressure, structural deflection, building vibration, and internal chemical reactions with gas components (such as sulfur compounds and moisture). The International Fuel Gas Code approves four primary piping materials, each governed by strict ASTM/ANSI manufacturing standards and installation limitations:

+---------------------------------------------------------------------------------------------------+
|                         APPROVED FUEL GAS PIPING MATERIALS & STANDARDS                            |
+-----------------------+---------------------+-----------------------------------------------------+
| Piping Material       | Standard Citation   | Code Applications & Restrictions                    |
+-----------------------+---------------------+-----------------------------------------------------+
| Schedule 40 Steel     | ASTM A53 / A106     | Standard aboveground interior & exterior; threaded  |
| (Black or Galvanized) |                     | or welded; malleable iron fittings.                 |
| CSST (Flexible)       | ANSI LC 1 / CSA 6.26| Interior distribution; continuous runs; requires    |
|                       |                     | 6 AWG electrical bonding jumper.                    |
| Copper Tubing         | ASTM B88 (Type K/L) | Permitted ONLY where gas has <= 0.3 grains H2S per  |
| (Seamless Drawn)      | ASTM B280 (ACR)     | 100 cu ft; brazed (>1000°F) or flared joints only.  |
| Polyethylene (PE)     | ASTM D2513          | OUTDOOR UNDERGROUND ONLY; min 18 AWG tracer wire;   |
| Plastic Pipe          |                     | strictly banned inside or under buildings.          |
+-----------------------+---------------------+-----------------------------------------------------+

Material Specifics & Restrictions

1. Schedule 40 Metallic Pipe (ASTM A53 / ASTM A106):
   • Standard black carbon steel pipe is the workhorse of commercial and residential gas distribution.
   • Threaded connections use American National Standard Taper Pipe Threads (ASME B1.20.1 NPT).
   • May be plain black steel or hot-dipped galvanized. Galvanized steel is frequently required outdoors or in damp basements to prevent external atmospheric oxidation.
2. Corrugated Stainless Steel Tubing (CSST - ANSI LC 1):
   • Engineered flexible tubing fabricated from ASTM A240 300-series austenitic stainless steel with an exterior yellow or black extruded polyethylene jacket.
   • Cuts installation labor by allowing continuous snaked runs through floor joists and wall cavities without intermediate joints.
   • Must be installed with manufacturer-specific listed mechanical brass mechanical fittings.
3. Copper & Brass Tubing (ASTM B88 Type K or L):
   • The Hydrogen Sulfide ($H_2S$) Rule: Copper reacts chemically with hydrogen sulfide in fuel gas to form flaky copper sulfide ($Cu_2S$). These flakes peel off the inner pipe walls and travel downstream, clogging gas orifices, safety valves, and pilot burners. Consequently, IFGC Section 403.4.3 restricts copper tubing strictly to areas where the serving utility certifies that gas contains not more than 0.3 grains of hydrogen sulfide per 100 standard cubic feet of gas ($0.7\text{ mg}/100\text{ L}$). If this purity cannot be guaranteed in writing, copper is strictly prohibited.
   • Joining requires approved 45-degree SAE flared fittings or brazed joints using filler metals with a melting point exceeding 1,000°F (538°C) (AWS BCuP or BAg). Soft solder ($< 1,000^\circ\text{F}$) is illegal on fuel gas.
4. Polyethylene (PE) Pipe (ASTM D2513):
   • Yellow thermoplastic pipe designed exclusively for outdoor underground burial.
   • Heat-fusion welded (butt, socket, or electrofusion) or joined by approved mechanical compression fittings.
   • ABSOLUTE CODE BAN: Polyethylene pipe can never be installed above ground, inside a building, or beneath a concrete slab foundation. It must transition to metallic pipe outside the building foundation wall.

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2. Underground Plastic Piping & Anodeless Risers (IFGC Section 404)

Buried fuel gas piping represents an extreme hazard if struck by excavators or subjected to frost heave. The International Fuel Gas Code enforces strict depth, tracing, and entry mandates:

                     UNDERGROUND POLYETHYLENE GAS SERVICE INSTALLATION

  GRADE LEVEL
  ===============================\====================================================
                                  \  YELLOW INSULATED COPPER TRACER WIRE (MIN 18 AWG)
    MINIMUM COVER DEPTH:           \ (Taped to pipe; terminates above grade at riser)
    12" Standard Earth             v
    18" Under Driveways   +-----------------------+
                          | ASTM D2513 PE PIPE    | ======================>
                          +-----------------------+                         \
                                                                             \
                   +----------------------------------------------------------+ 
                   | FACTORY-ASSEMBLED ANODELESS RISER (OUTSIDE WALL ONLY)    |
                   | - Buried PE heat-fused to internal PE carrier inside     |
                   | - Heavy Schedule 40 steel protective outer casing        |
                   | - Gas-tight casing seal above grade                      |
                   | - Transition to rigid steel BEFORE entering building     |
                   +----------------------------------------------------------+

Mandatory Underground Rules

1. Minimum Burial Depth: Underground piping must be installed with a minimum depth of cover of 12 inches (305 mm). Where external surface damage or vehicular traffic is anticipated (such as under residential driveways or commercial parking pads), the minimum depth of cover must be increased to 18 inches (457 mm).
2. Tracer Wire Mandate (IFGC Section 404.17.3): Because polyethylene plastic cannot be located using electromagnetic pipe locators, an insulated copper tracer wire of not less than 18 AWG (typically yellow-jacketed for fuel gas identification) must be buried in the trench immediately adjacent to the plastic pipe. The tracer wire must terminate above grade at each end of the run (e.g., at the meter riser and building wall) with accessible test leads for utility locator hookup.
3. Factory Anodeless Risers: Plastic gas pipe cannot penetrate above grade. The transition from buried PE to aboveground metallic pipe must be executed using a listed factory-assembled anodeless riser. The steel riser casing provides physical protection against impact and UV degradation while isolating the plastic carrier from atmospheric exposure.

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3. Prohibited Fittings, Materials & Routing Practices

To prevent catastrophic structural failure, embrittlement, or hidden gas leaks, the International Fuel Gas Code strictly outlaws several traditional plumbing practices:

+---------------------------------------------------------------------------------------------------+
|                         STRICTLY PROHIBITED GAS PIPING PRACTICES                                  |
+-----------------------+---------------------------------------------------------------------------+
| Prohibited Item       | Code Failure Pathology & Safety Hazard                                    |
+-----------------------+---------------------------------------------------------------------------+
| Cast Iron Fittings    | Brittle crystalline structure; cracks under settling or thermal expansion.|
| Threaded Bushings     | Hex/face bushings thin out pipe wall thickness and shear off easily.      |
| Concealed Threads     | Threaded joints cannot be concealed in walls, partitions, or floors.      |
| Soft Solder Joints    | Low melting point (<1,000°F); melts rapidly during structural fires.       |
| Mechanical Connectors | Flexible appliance connectors cannot penetrate walls, floors, or cabinets.|
| Prohibited Routing    | Gas piping cannot pass through air ducts, plenums, clothes chutes, vents. |
+-----------------------+---------------------------------------------------------------------------+

Detailed Analysis of Code Prohibitions

• Prohibition on Threaded Bushings (IFGC Section 403.10.4): Threaded hex or face bushings are strictly outlawed in gas piping. When a bushing is screwed into a fitting, it reduces mechanical wall thickness, leaving insufficient material to withstand pipe wrench torque or thermal stress. Plumbers must use concentric reducing couplings or swaged reduction fittings.
• Concealed Piping Restrictions (IFGC Section 404.5): Gas piping concealed inside stud cavities, ceiling spaces, or floors must be welded, brazed, or continuous tubing (such as uncut CSST runs). Threaded fittings, unions, compression couplings, and valves are strictly prohibited inside concealed spaces because micro-leaks cannot be detected or tightened.
• Prohibited Enclosures (IFGC Section 404.3): Gas piping cannot run inside air ducts, plenums, chimneys, gas vents, dumbwaiter shafts, clothes chutes, or elevator hoistways.

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4. CSST Electrical Bonding Mandates (IFGC Section 310 & NEC Article 250)

Corrugated Stainless Steel Tubing (CSST) features ultra-thin stainless steel wall convolutions (typically $0.010$ to $0.012$ inches thick). While extremely flexible, this thin wall makes standard yellow-jacketed CSST highly vulnerable to indirect lightning strikes:

                         THE CSST LIGHTNING ARCING HAZARD

  LIGHTNING STRIKE NEARBY =====> Ground Potential Surge across building
                                    |
                                    v
     [High Voltage Charge on CSST] ======= (Electrical Arc) ======> [Grounded Copper Pipe,
                                           (Punctures 0.010" wall)    Ductwork, or Rebar]
                                                    |
                                                    v
                                        GAS UNDER PRESSURE ESCAPES
                                        AND IGNITES INTO JET FIRE

The Direct Bonding Solution (IFGC Section 310.1)

To prevent lightning voltage differentials from arcing through the tubing wall, standard yellow CSST must be directly bonded to the electrical service grounding electrode system:

1. Bonding Conductor Size: The bonding jumper must be a solid or stranded copper conductor of not less than 6 AWG.
2. Bonding Clamp Attachment: The bonding jumper must connect to a metallic pipe component (such as a rigid steel pipe nipple or a CSST brass fitting) located upstream of the first CSST fitting, as close to the gas service entrance or meter as practical.
3. Grounding Termination: The opposite end of the 6 AWG copper jumper must bond directly to one of the following:
   • The electrical service equipment enclosure (panelboard ground bus).
   • The grounded electrical service entrance conductor.
   • The electrical service grounding electrode conductor (GEC).
   • The grounding electrode system (e.g., ground rods, concrete-encased electrode / Ufer ground).
4. Arc-Resistant CSST (Black Jacket / ANSI LC 1 Section 5.16): Modern CSST featuring an engineered, black conductive jacket that dissipates electrical energy does not require the additional 6 AWG direct bonding clamp if installed strictly per the manufacturer's listing and local AHJ approval.

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5. Pipe Hangers & Support Spacing (IFGC Table 415.1)

Fuel gas piping must be securely anchored to structural framing to eliminate sags, vibrations, and mechanical stress on joints. Gas lines must never be supported by other piping, electrical conduits, or ceiling suspended grid wires.

+---------------------------------------------------------------------------------------------------+
|                         FUEL GAS PIPE HANGER SPACING (IFGC TABLE 415.1)                           |
+-----------------------------+-----------------------------------+---------------------------------+
| Pipe Material & Size        | Maximum Horizontal Spacing (Feet) | Maximum Vertical Spacing (Feet) |
+-----------------------------+-----------------------------------+---------------------------------+
| 1/2" Steel Pipe             | 6 feet                            | Every floor level               |
| 3/4" and 1" Steel Pipe      | 8 feet                            | Every floor level               |
| 1-1/4" and Larger Steel     | 10 feet                           | Every floor level               |
| 1-1/4" and Larger (Nominal) | 10 feet                           | Max 15 feet between supports    |
| 1/2" CSST Tubing            | 4 feet                            | Every floor level (max 10 ft)   |
| 3/4" and 1" CSST Tubing     | 6 feet                            | Every floor level (max 10 ft)   |
| 1-1/4" and Larger CSST      | 8 feet                            | Every floor level (max 10 ft)   |
| 1/2" Copper Tubing          | 4 feet                            | Every floor level               |
| 5/8" and 3/4" Copper Tubing | 6 feet                            | Every floor level               |
| 7/8" and 1" Copper Tubing   | 8 feet                            | Every floor level               |
+-----------------------------+-----------------------------------+---------------------------------+

Physical Shielding & Striker Plates (IFGC Section 404.7)

Where gas piping passes through wood studs, joists, or rafters and the outer edge of the pipe is less than 1-1/2 inches (38 mm) from the nearest edge of the structural wood member, the piping must be protected from drywall screws and construction nails by hardened steel shield plates (striker plates). Shield plates must be not less than No. 16 gauge (0.0598 inch / 1.5 mm) steel and must extend at least 4 inches (102 mm) beyond each side of the framing member.

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6. Realistic Exam Application Scenarios

Scenario A: Outdoor Gas Line to a Detached Garage

Exam Scenario: A journeyman plumber is running a natural gas line from an existing residential basement to a detached garage 60 feet away to supply an 80,000 BTU/h unit heater. The plumber installs Schedule 40 black steel inside the basement, core-drills the foundation wall, runs ASTM D2513 yellow polyethylene pipe through the wall, buries it 10 inches deep in the yard, enters the garage through the concrete slab with the plastic pipe, and connects directly to the heater. What violations did the inspector cite?

Code Analysis:

1. Violation 1 — Burial Depth (IFGC 404.12): The 10-inch burial depth violates the minimum 12-inch requirement.
2. Violation 2 — Plastic Inside/Under Buildings (IFGC 404.14): ASTM D2513 polyethylene pipe is strictly prohibited from passing through foundation walls, running under concrete slabs, or entering the interior of any building.
3. Violation 3 — Missing Anodeless Risers: The transition from indoor steel to outdoor plastic, and from underground plastic to garage steel, must be made outdoors above grade using factory-assembled anodeless risers.
4. Violation 4 — Missing Tracer Wire (IFGC 404.17.3): Buried plastic pipe requires an adjacent insulated yellow copper tracer wire (minimum 18 AWG) terminated above grade.

Scenario B: Inspection of a Remodeled Mechanical Room

Exam Scenario: During an inspection of a multi-family boiler room in Detroit, the inspector observes a 1-1/2-inch Schedule 40 gas main reduced to 1-inch to feed a water heater using a cast iron threaded hex bushing. The branch line then transitions to yellow CSST routed through a supply air plenum, with no visible grounding clamp attached. What corrective actions are required?

Code Analysis:

1. Illegal Fitting (IFGC 403.10.4): Threaded bushings and cast iron fittings are illegal. The plumber must replace the cast iron hex bushing with a steel concentric reducing coupling or swaged nipple.
2. Illegal Routing (IFGC 404.3): Fuel gas piping cannot pass through an air plenum. The CSST must be re-routed outside the ductwork/plenum.
3. Missing Electrical Bonding (IFGC 310.1): Standard yellow CSST must be directly bonded using a minimum 6 AWG copper jumper clamped to the rigid steel header and connected to the main electrical service grounding electrode.