10.1 Piping & Tubing Materials: Steel, Copper, CSST & Plastic

Piping & Tubing Materials: Steel, Copper, CSST & Plastic

In Ontario, the selection, handling, and installation of fuel gas piping and tubing are legally governed by Ontario Regulation 212/01 (Gaseous Fuels) and the CSA B149.1 Natural Gas and Propane Installation Code. Because fuel gases such as natural gas (predominantly methane, $CH_4$) and propane ($C_3H_8$) are flammable, pressurized, and potentially asphyxiating, the materials conveying them must exhibit rigorous mechanical strength, chemical resistance, and pressure containment. Clause 6 of CSA B149.1 defines the precise metallurgical standards, allowable operating environments, and structural limitations for all approved piping and tubing materials.

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1. Steel Gas Piping and Fitting Specifications

Rigid carbon steel pipe—commonly referred to in the trade as "black iron" pipe—remains the industry standard for residential, commercial, and industrial gas distribution due to its exceptional tensile strength, structural rigidity, and resistance to external mechanical impact and elevated fire temperatures.

Approved Manufacturing Standards

Steel pipe for gas distribution is manufactured to recognized standards such as these (Clause 6.2 lists the accepted materials):

• ASTM A53 / A53M: Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless (Grade A or Grade B).
• ASTM A106 / A106M: Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service.
• API 5L: Specification for Line Pipe (American Petroleum Institute).

Wall Thickness: What CSA B149.1-25 Requires

Steel pipe is identified by nominal pipe size (NPS) and wall schedule. CSA B149.1-25 Clause 6.2.3 sets the minimum schedule:

Two related rules matter for threaded work:

• Clause 6.3.8.1: for natural gas, threaded pipe and fittings smaller than NPS 1/2 must be Schedule 80.
• Clause 6.9.2: piping of NPS 2-1/2 to 4 is joined with certified press-connect fittings or welded joints, and piping larger than NPS 4 is welded or welded-flanged.

Threading removes wall material at the thread roots, which is why the press-connect option exists for light-wall pipe: Schedule 10 is never threaded. Residential threaded gas piping is therefore Schedule 40 black steel.

Restrictions on Galvanized Steel Pipe

Galvanized steel pipe is standard black steel that has undergone a hot-dip zinc coating process to protect against atmospheric moisture oxidation. However, its use in fuel gas systems is subject to strict chemical restrictions:

• Hydrogen Sulfide Contamination: Some gas supplies (for example untreated or biogas sources) can contain traces of hydrogen sulfide ($H_2S$) and moisture. Hydrogen sulfide reacts chemically with the interior zinc galvanized lining to form zinc sulfide ($ZnS$) flakes:

$H_2S + Zn \rightarrow ZnS\downarrow + H_2$

• Orifice and Valve Fouling: Over time, these brittle zinc sulfide flakes spall off the pipe wall and are carried downstream by the gas stream. The debris accumulates inside the fine ports of pilot orifices, burner orifices, and the delicate elastomer seats of appliance safety shut-off valves, causing flame rollout, pilot failure, or failure of the gas valve to close tightly.
• In Practice: black steel is the normal choice for gas piping in Ontario; galvanized pipe appears mainly on exposed outdoor runs. Check Clause 6.2 and the gas supplier before choosing it.

Fitting Standards: Malleable Iron vs. Prohibited Cast Iron

Fittings used with threaded steel gas pipe must withstand substantial tightening torque and cyclic building vibrations:

• Approved Malleable Iron (ASME B16.3 Class 150 / Class 300): Malleable iron undergoes an extensive annealing heat-treatment process that imparts ductility. Under mechanical stress or extreme temperature changes, malleable iron deforms slightly rather than fracturing.
• Avoid Grey Cast Iron (ASME B16.4): Use malleable iron or steel fittings; ordinary grey cast iron fittings are unsuitable for gas piping. Cast iron is exceptionally brittle and contains crystalline graphite flakes that create internal stress planes. When subjected to the tightening torque of heavy pipe wrenches, physical impacts, or thermal shock during a structural fire, cast iron fractures instantly with zero plastic deformation, resulting in catastrophic gas blowouts.

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2. Copper Tubing Specifications & Chemical Limitations

Copper tubing provides excellent corrosion resistance, smooth internal flow characteristics, and mechanical flexibility that simplifies routing through finished building cavities without cutting and threading numerous short pipe nipples.

Permitted Copper Types (ASTM B88 & ASTM B837)

Copper tubing for gas must be seamless and of a type permitted by Clause 6.2:

• ASTM B88 Type K (Green Marking): Heavy wall thickness; approved for underground burial, exterior distribution, and interior gas piping.
• ASTM B88 Type L (Blue Marking): Medium wall thickness; the most common copper tubing utilized for interior above-ground natural gas and propane branch lines.
• ASTM B837 Type G: seamless copper tube made specifically for natural gas and propane distribution, often supplied with a yellow outer coating.

The Absolute Prohibition of Type M Copper

ASTM B88 classifies copper tubing into three primary wall thicknesses: Type K (thickest), Type L (medium), and Type M (thinnest, marked with red ink):

Hydrogen Sulfide and Internally Tinned Copper

Just as zinc reacts with hydrogen sulfide, unalloyed copper reacts aggressively with sulfur compounds present in "sour" fuel gases. When copper is exposed to hydrogen sulfide, it forms black copper sulfide ($Cu_2S$) scale:

$2Cu + H_2S \rightarrow Cu_2S\downarrow + H_2$

This brittle black scale flakes off the inner tube wall, rapidly obstructing narrow gas passages in combination gas valves and modulating pilot controls.

Annealed (Soft) vs. Hard-Drawn Copper

Copper tubing is supplied in two metallurgical tempers:

1. Annealed (Soft Coiled): Annealed through thermal heating, allowing the tubing to be bent smoothly around obstructions using approved mechanical lever-type tube benders. Coils up to $100\text{ feet}$ ($30\text{ m}$) allow continuous joint-free runs under subfloors and inside partition walls.
2. Hard-Drawn (Rigid Lengths): Cold-drawn straight lengths (typically $12\text{ ft}$ or $20\text{ ft}$) providing high rigidity and a neat, professional appearance for exposed mechanical room installations. Hard-drawn copper cannot be bent in the field and must be joined using brazed wrought copper fittings.

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3. Corrugated Stainless Steel Tubing (CSST)

Corrugated Stainless Steel Tubing (CSST) consists of a continuous, thin-walled, flexible core of austenitic stainless steel (AISI Grade 304 or 316) covered with an extruded polyethylene protective jacket. CSST combines the routing flexibility of electrical armored cable with the gas-tight integrity of metal piping, dramatically reducing installation labor and eliminating the numerous threaded fittings required by rigid pipe.

Certification and System Compatibility

CSST systems must be tested and certified to CSA 6.26 / ANSI LC 1 (Fuel Gas Piping Systems Using Corrugated Stainless Steel Tubing). A fundamental rule of CSST installation is that CSST is an engineered proprietary system:

• Mechanical brass fittings, split rings, and adapters are engineered to mate with the specific convolution geometry of that manufacturer's tubing.
• Never intermix components: Fittings manufactured by Gastite, TracPipe (OmegaFlex), WardFlex, or Pro-Flex cannot be interchanged. Mixing components from different manufacturers immediately voids the certification listing and warranty, violates CSA B149.1 Clause 4.1.3, and frequently results in gas leakage due to improper mechanical bite.

Physical Protection: Striker Plates

Because the corrugated stainless steel wall is thin, it is vulnerable to puncture by drywall screws, framing nails, and picture hangers. CSST manufacturers therefore require:

• Hardened steel striker plates, of the type and size the manufacturer specifies, wherever CSST passes through studs, joists or plates close enough to the face for a fastener to reach it.
• Striker plates prevent fasteners from reaching the tubing by deflecting screws and nails before they contact the stainless steel core.

Electrical Bonding Mandate for CSST

Standard yellow-jacketed CSST installations present a unique electrical hazard during lightning storms. While direct lightning strikes destroy electrical and mechanical systems, indirect (cloud-to-ground) lightning strikes induce severe transient electrical voltage surges into building structural steel, electrical wiring, and plumbing networks.

+-------------------------------------------------------------+
|                  LIGHTNING SURGE HAZARD                     |
|                                                             |
|   Indirect Lightning Strike -> Transient Voltage Surge      |
|   Voltage Differential -> Electrical Arc from CSST to Duct  |
|   Arcing Energy -> Melts Hole in Thin Stainless Wall        |
|   Result: Pressurized Gas Blowout & Fire Inside Wall Void   |
+-------------------------------------------------------------+

When a transient surge seeks ground, an electrical potential difference (voltage gradient) develops between the unbonded CSST and adjacent grounded metal objects (such as sheet metal ductwork, electrical conduits, or copper water pipes). When the breakdown voltage of the thin yellow polyethylene jacket is exceeded, an intense electrical arc jumps between the CSST core and the grounded metal. The energy of this arc can burn a pinhole through the thin stainless steel wall, allowing pressurized gas to escape and ignite inside concealed wall or floor cavities.

Bonding Requirements under CSA B149.1-25 and the Electrical Code

CSA B149.1-25 reorganized the bonding rules to match the Canadian Electrical Code:

• Clause 4.7.3: all building metal gas piping connected to one or more gas appliances is made electrically continuous and equipotentially bonded—by a conductor no smaller than No. 6 AWG copper or No. 4 AWG aluminum with a connection that stays accessible, by meeting the electrical code, or as Clause 4.7.4 permits.
• Clause 4.7.4: the piping system—including CSST with an arc-resistant jacket certified to CSA/ANSI LC 1/CSA 6.26—is considered bonded when it is connected to appliances that are permanently connected to the bonding conductor of their supply circuit.
• Clause 4.7.5: CSST without an arc-resistant jacket must also be bonded as the CSST manufacturer's instructions require (typically a bonding conductor attached to a rigid pipe component or brass fitting near the start of the CSST run, never to the corrugated tubing itself).
• Clause 6.14.6: gas piping must never be used as an electrical ground.

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4. Polyethylene (PE) Plastic Piping for Underground Distribution

Thermoplastic polyethylene (PE) piping has completely supplanted metallic piping for buried outdoor fuel gas distribution. PE pipe is impervious to electrolytic soil corrosion, acidic ground conditions, and galvanic degradation that aggressively attacks buried steel.

Manufacturing Standards and Color Identification

Plastic pipe, tubing and fittings (CSA B149.1 Clauses 6.2.14–6.2.20) must conform to:

• ASTM D2513: Standard Specification for Thermoplastic Gas Pressure Pipe, Tubing, and Fittings, or CSA B137.4.
• Colour: PE gas pipe is normally yellow (or carries yellow identification) so excavators recognize it.

Crucial Installation Limitations: Underground Outdoors Only

Minimum Burial Depths (Ontario CAD Clause 6.15.4)

To protect against surface excavation, frost heave, and crushing loads from surface traffic, underground PE gas piping must satisfy strict minimum cover depths:

Add cover where damage is likely (for example farm operations). Where gas and electrical systems share a common trench, CSA B149.1-25 Clause 6.15.15 requires at least 12 in. (300 mm) of separation.

PE pipe must be bedded in clean, rock-free sand or fine backfill to prevent sharp stones from puncturing or grooving the pipe wall during soil compaction.

Anodeless Risers and Transition Fittings

Because polyethylene cannot emerge above ground, the transition from buried plastic to metallic pipe must occur below grade:

• Anodeless Riser: A factory-manufactured assembly featuring a steel protective outer casing that houses a plastic PE core. The mechanical transition from PE to Schedule 40 steel occurs underground inside the sealed casing.
• The steel riser extends vertically above grade, providing complete mechanical shielding and UV protection, terminating in an exterior standard male NPT threaded connection for meter or regulator attachment.

Mandatory Tracer Wire for Utility Locating

Because polyethylene does not conduct electricity, buried plastic gas lines cannot be found by standard electromagnetic pipe locators, so a tracer wire is installed with them (Clause 6.15):

• A dedicated tracer wire must be buried in the trench directly alongside the plastic pipe.
• Tracer Wire Specification: Use the insulated, corrosion-resistant tracer wire the code and the pipe manufacturer specify (solid copper is common).
• Installation Protocol: The tracer wire must be laid loosely beside the pipe (never wrapped tightly around it, which attenuates the signal) and must terminate above grade at each anodeless riser. The exposed ends must remain accessible inside an approved junction box or test station to allow utility technicians to connect transmitter clips for locating.

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5. Fuel Gas Piping Material Comparison