Both are code-approved when installed right. Black iron pipe is rigid, threaded, very durable, and cheaper in material. CSST is flexible stainless tubing that installs faster with fewer fittings. CSST must be bonded to your electrical grounding system to lower the risk of lightning damage.
What black iron and CSST gas pipe actually are
Black iron pipe is rigid steel pipe with threaded joints. A fitter cuts it to length, cuts threads on each end, and screws on elbows, tees, and couplings sealed with pipe dope or gas-rated tape. The wall is thick, the pipe is heavy, and once it is assembled it does not move. That thick wall is the reason black iron shrugs off physical knocks and resists damage from electrical energy. The downside is labor. Every joint takes time to thread, fit, and leak-test, so a long run with many turns eats hours.
CSST stands for corrugated stainless steel tubing. It is thin, flexible stainless steel covered in a plastic jacket, usually yellow, though a newer black jacket carries an arc-resistant coating. Because it bends around corners and frames, a crew can pull one continuous length from the manifold to an appliance with far fewer fittings. That cuts install time, which is why builders adopted it widely. The cost trade runs the other way: the tubing and its mechanical fittings cost more per foot than threaded black steel.
Both materials are listed and approved for fuel gas under the International Fuel Gas Code (IFGC) and NFPA 54, the National Fuel Gas Code. Neither is "banned." The right pick depends on the run, the budget, and correct installation.
One more point on appearance. Black iron is what most people picture when they think of a gas line: dull gray-black steel with screwed fittings. CSST looks nothing like it. The yellow jacket is the common version, while the newer black jacket carries the arc-resistant coating that adds a layer of protection against electrical energy. Seeing yellow or black flexible tubing in an attic or crawlspace is a quick sign the home uses CSST, which tells you the bonding rule below applies.
The CSST safety rule you cannot skip: bonding
Lead with this if you take one thing away. CSST must be electrically bonded and grounded to the home's electrical service grounding electrode system. The bonding conductor must be not smaller than 6 AWG copper, per IFGC Section 310.2 and IRC Section G2411.2, which align with NFPA 54. The bonding clamp attaches to a brass fitting or rigid pipe component, not to the tubing itself, and ties the gas system into the same ground as the electrical service.
Here is why it matters. CSST has a thin wall. When lightning hits at or near a house, it can energize metal systems and seek a path to ground. If the gas piping is not bonded, the electrical energy can jump, or arc, between the CSST and another grounded metal object nearby. That arc can burn a tiny hole through the thin tubing wall and release gas, which can ignite. Bonding gives the energy a safe, low-resistance path to ground and lowers the odds of an arc. Black iron's thick wall is far less likely to be punctured this way, which is one reason it is treated as the more forgiving material near electrical risk.
The code language is direct. As ICC CodeNotes puts it, "CSST gas piping systems must be electrically continuous and bonded to the electrical service grounding electrode system." Manufacturers say the same. The Gastite installation guide requires a bonding clamp and a conductor sized to code, attached as close as practical to where the gas line enters the building. If a home has CSST and no visible bonding jumper near the meter or manifold, that is a red flag worth checking. Arc-resistant black-jacketed CSST adds a protective layer, but it does not remove the bonding requirement.
A common point of confusion is the difference between bonding and the standard grounding an electrician already does at the panel. The bonding jumper for CSST is a separate, dedicated connection from the gas system to that same grounding point. It is sized at 6 AWG copper as a minimum because the conductor has to carry a large surge without burning open. Skipping it, undersizing it, or clamping it to a painted or corroded surface defeats the purpose. This is one reason CSST should be installed by a licensed pro who knows the rule and will leave the connection visible for the inspector to confirm.
Side-by-side comparison
The table below lines up the points that drive most decisions. Use it to match the material to your job.
| Factor | Black iron (steel) pipe | CSST (corrugated stainless tubing) |
|---|---|---|
| Form | Rigid, threaded joints | Flexible, bends around corners |
| Install speed | Slower; each joint threaded and sealed | Faster; fewer fittings, long runs |
| Material cost | Lower | Higher |
| Labor cost | Higher (more time per joint) | Lower (quicker pulls) |
| Wall thickness | Thick, very durable | Thin |
| Lightning / arc risk | Lower; thick wall resists puncture | Higher if not bonded; requires 6 AWG bonding |
| Physical damage | Resists knocks well | Needs protection from nails, screws, abrasion |
| Bonding required | Standard electrical bonding | Dedicated bonding to grounding system, code-required |
| Code status | Approved (IFGC / NFPA 54) | Approved (IFGC / NFPA 54) |
A few notes on the table. CSST saves the most on labor in homes with long, twisty runs, such as feeding a rooftop unit or a far-corner appliance. Black iron wins on raw durability and tends to cost less in material, so it stays popular for short, straight runs and exposed pipe in garages or mechanical rooms where it might take a bump. CSST also needs striker plates where it passes through studs and joists so a future drywall screw or nail cannot pierce the thin wall.
Which one should you choose
For most Phoenix homeowners, the honest answer is that a licensed gas contractor picks the material that fits the run, and either one is safe when installed to code. If your job is a short, exposed line to a water heater, range, or dryer, black iron is durable, lower in material cost, and simple to inspect. If your job is a longer run with many turns, an attic pull, or a remodel where speed and flexibility help, CSST can lower labor cost and time.
The deciding safety factor is installation quality, not the brand on the box. CSST is only as safe as its bonding. Confirm that any CSST in your home is bonded with a conductor no smaller than 6 AWG copper tied to the grounding electrode system, that it is protected from punctures, and that the whole system passed the required pressure test before it was put into service. Black iron asks for fewer special steps but still needs proper sizing, support, and a leak test.
In Phoenix, any gas piping work needs a permit and an ROC-licensed contractor, and the system must pass an inspection and pressure test before connection. If you are adding a line for a pool heater, fire pit, or outdoor kitchen, the same rules apply. To plan that work, see our pages on who can install a gas line in Arizona and the cost to add a gas line. A short consultation with a licensed pro will match the material to your home and confirm the bonding and testing are done right.