Buried steel gas lines fail mostly from corrosion. Once the protective coating is scraped, cracked or worn at joints, soil and moisture eat the steel until it leaks. Galvanizing doesn't protect gas pipe underground. Code-compliant replacements are polyethylene plastic with a tracer wire, or factory-coated steel, buried at least 12 inches deep.
What makes buried steel gas pipe corrode?
Bare steel touching damp soil, mostly. Section 404.11 of the 2024 International Fuel Gas Code, which Phoenix enforces, says buried steel pipe has to be protected from corrosion. Section 404.11.2 accepts three approaches:
- Corrosion-resistant material suited to the soil.
- A factory-applied, electrically-insulating coating, with every fitting and joint coated per the coating maker's instructions.
- A cathodic protection system, "monitored and maintained in accordance with an approved program."
Each of those points to a way older lines fail:
| Weak spot | What goes wrong | Code rule it breaks |
|---|---|---|
| Galvanized or bare steel in the ground | Zinc wears away and the steel under it rusts | 404.11.1: zinc isn't adequate protection |
| Threaded joints and fittings left unwrapped | Bare metal at every joint | 404.11.2: joints must be coated |
| Coating nicked by rocks or tools at install | Corrosion starts at the scratch | 404.11.2: coating must be intact |
| Copper or brass joined to steel underground | The two metals set up a galvanic cell | 404.11.3: insulating coupling required |
| Cathodic protection never checked | Anodes used up, protection gone | 404.11.2: an approved program must maintain it |
Chandler's permit manual shows how a city applies this in the field. Buried metal gas pipe needs a factory-applied coating and at least Schedule 40 weight. Field wrapping is only for fittings and short damaged spots, using "2 layers of 20 mil tape with primer." And "Galvanized fittings or piping are prohibited in underground gas systems."
Other buried-line problems happen too: a line damaged by digging, a line that ends up under a building addition, or a line too shallow after regrading. Section 404.12 sets burial at a minimum of 12 inches below grade for most underground gas piping.
What are the warning signs of a leaking buried gas line?
Southwest Gas lists the signs of a leak. You may:
- Smell "a distinct sulfur-like odor, similar to rotten eggs, even if it's faint or momentary."
- Hear "a hissing or roaring coming from the ground, aboveground piping, or a natural gas appliance."
- See "dirt or water blowing into the air, unexplained dead or dying plants or grass, or standing water continuously bubbling."
Around a commercial building, that might look like a dead strip of landscaping along the path from the meter bank, or a puddle that keeps bubbling after the irrigation shuts off. If the utility finds a hazard on customer piping, it can shut off service until the repair is made. In Phoenix, a meter locked for a leak on the customer side needs a city permit, inspection and clearance before gas comes back.
If you notice any of those signs, don't dig or test it yourself. Get people away from the area, then call 911 and Southwest Gas at 877-860-6020 from a safe place.
### How do you check an old line before it fails?
A plumber has a few ways to check a buried line without digging it all up:
- A pressure test. With the line isolated, the plumber pressurizes it and watches a gauge. Section 406.5 of the code treats any pressure drop as a leak unless another cause is clear.
- A leak survey along the route. Section 406.5.1 names a listed combustible gas detector or leak-detecting fluid as the ways to find a leak.
- A look at the risers. Where the pipe comes out of the ground at the meter and the building, a plumber can often see the coating and the steel.
If a line is old, bare, galvanized or already patched, plan its replacement before it fails on a busy day.
Who owns the buried gas line at a commercial property?
The property owner does, from the meter outlet to the building. Southwest Gas calls it a customer-owned yard line. The utility owns the lines up to and including the meter, and "COYLs must be maintained by the property owner." Older buildings often have the meter far from the building, which leaves the owner more buried pipe. Southwest Gas's brochure adds that customer buried piping includes "piping to outdoor appliances," such as lines to restaurant patio heaters and fire pits.
Federal pipeline rules make the utility say this in writing. Under 49 CFR 192.16, the gas company must warn customers that buried piping it doesn't maintain "may be subject to the potential hazards of corrosion and leakage." The notice says the pipe should be checked for leaks, checked for corrosion if it's metal, and repaired if unsafe. It also says plumbing contractors can help locate, inspect and repair it.
Two practical catches:
- 811 won't mark it. Southwest Gas warns that "customer buried piping can't be located by calling 811." You need your own locate before digging near it.
- In a strip center, the lease decides who pays. Our page on who owns the gas piping in a strip center covers the landlord and tenant split.
### What about moving the meter instead?
Sometimes that's the better fix. Southwest Gas's brochure offers it as an option. You pay to move the meter next to the building, which "will greatly reduce, or even eliminate, the pipe for which you're responsible." For a long, failing yard line, compare the cost of a new line against a meter relocation plus a short new run. Southwest Gas takes meter relocation questions at 800-654-2765.
What replaces a failed underground steel gas line?
The two common choices are polyethylene (PE) plastic pipe and factory-coated steel. Plastic can't come above ground on its own, so it rises through an approved riser. The code sets the rules for plastic in Section 404.17:
- Outdoors and underground only. "Plastic pipe shall be installed outdoors underground only," and not "within or under any building or slab." Outdoor patio, walkway and driveway slabs are an exception if the burial depth is met.
- A tracer wire. A yellow insulated copper wire, "not less than 18 AWG," runs alongside so the line can be found later, with access at each end.
- Proper transitions. Plastic-to-metal connections underground use listed transition fittings, and plastic comes above ground in anodeless risers or an approved adapter.
- Burial depth. At least 12 inches under Section 404.12. Individual lines to outdoor lights, grills and similar appliances can be 8 inches where approved and safe from damage.
Coated steel is still used where plastic isn't allowed or practical, installed with every joint wrapped. And no gas pipe goes underground beneath a building except inside a protective conduit, per Section 404.14.
The replacement is permit work. Phoenix's gas clearance table lists any new gas piping, and repairs where the gas was shut off, as needing a permit, a city inspection and a clearance. The new line is pressure tested before it's covered. Our guide to how a gas line pressure test works walks through it.
HQ Plumbing & Air locates, repairs and replaces buried commercial gas lines across the Phoenix area, including permits, testing and the city clearance, with 24/7 emergency service for leaks. You get a free estimate and the price up front.
Buried steel lasts as long as its coating does. Check yours before it tells you.