Can a gas line be replaced without digging?

A common reason is the coated steel pipe between the gas meter and the house. The code requires buried steel gas pipe to be protected from corrosion (Section 404.11 of the fuel gas code Phoenix enforces), and older coated steel loses that protection where the wrap was nicked or has broken down. Once one spot leaks, the rest of the run is usually the same age and in the same soil, so replacing the whole run often makes more sense than patching it.

Southwest Gas is clear about whose pipe that is. It owns and maintains the piping "up to and including your meter," and all the piping between the meter and your structure, including piping to outdoor appliances, "is owned and must be maintained by you." The utility calls this customer buried piping. On some lots the meter sits at the property line, so that pipe can be a long run under the front yard and driveway, which is exactly when a trenchless job pays off.

Boring a new path

A small boring rig, or a pneumatic piercing tool for short runs, pushes a pilot path from one pit to the other under the yard, driveway or walk. The new gas pipe is pulled back through that path. The old line is disconnected at both ends and left in the ground. This is the usual choice when the old pipe takes an odd route, is badly corroded, or runs under something that should not be disturbed.

Pulling new pipe through the old one

When the old steel line is straight enough and open end to end, a smaller plastic gas pipe can be pushed or pulled through it. The old pipe becomes a casing around the new one. It is quick and follows the original route, but the new pipe has a smaller inside diameter than the old one, so the line has to be sized again for every appliance it feeds. Our guide to the longest length method shows how gas pipe is sized from the total BTU and the length of the run. A pool heater or a big tankless water heater on the end of a long run can rule this method out.

You may also hear about pipe bursting, where a head splits the old pipe and pulls the new one in behind it. It is common on water lines and sewer lines. On a short residential gas service, boring or pulling through is the more common choice.

Trenchless changes how the pipe gets in the ground, not the rules for the pipe.

• Plastic is for outdoors and underground only. Polyethylene gas pipe stays buried outside. It transitions to metal pipe before it comes out of the ground and enters the house, with a fitting made for that change.
• A tracer wire goes with it. Buried plastic gas pipe needs an insulated copper tracer wire, 18 AWG or larger, run with the pipe so a locator can find a line that metal detectors can't. In a bore, the wire is pulled in alongside the pipe.
• Burial depth. The general rule is at least 12 inches below grade, and 8 inches only for an approved line that serves an outdoor appliance alone. A bore can run deeper than a hand dug trench, which is fine. Our page on gas line burial depth in each Valley city lists the local amendments.
• No pipe under the slab without a conduit. Section 404.14 allows gas piping underground beneath a building only inside a protective conduit. So when the old line runs under the house, the new one is usually rerouted around the outside of the foundation instead of being bored under the slab.

A bore runs blind, and the sewer line from the house to the street is often where nobody expects it. If a gas line is bored straight through a sewer pipe, that is called a cross bore. It may cause no trouble for years, until someone clears a clog with a cutting head and cuts into the gas line inside the sewer. NASSCO, the sewer rehabilitation trade group, warns that gas cross bores through sewer laterals "can blow up houses," because the sewer lateral is "a direct conduit to the house."

Before a bore crosses the sewer's path, the sewer should be located. HQ Plumbing & Air runs a sewer camera from a cleanout, and the camera's line locator marks where the sewer runs, so the bore can be planned to miss it. Where a bore did cross the sewer route, running the camera again afterward confirms the sewer was not hit.

Arizona law says no one may begin excavating "before the location and marking are complete." Utilities have two working days to mark their lines after an excavator calls. Boring counts as excavation, so the pits and the bore path both wait for 811. Our page on Arizona's 811 law covers the rest of it.

811 marks the utilities' lines, not yours. Your own buried gas line, a sprinkler line, low voltage lighting or a line to a pool or detached garage won't be marked. Southwest Gas tells owners to "hand dig when excavating near any buried gas piping." This is one more reason the old line gets located before the new one goes in.

Replacing a buried gas line is an alteration to the gas piping system. The City of Phoenix's gas clearance list says "any new gas piping installation" and alterations to an existing gas piping system need a city permit, a city inspection and a city gas clearance. If Southwest Gas locked the meter after finding a leak on the customer side, the same three steps apply before the gas comes back on. Our page on a Southwest Gas red tag explains that lock-off.

The new line is pressure tested before it is buried or covered. On a trenchless job the inspector looks at the pipe and connections in the pits, along with the tracer wire and the transitions. Our page on gas line pressure tests covers what that test is.

A single leak on a line that is otherwise sound can be dug up and repaired at that spot. The pressure test tells you whether there is one leak or several. When the steel is corroded along its length, the line has failed the test more than once, or a new appliance needs a bigger pipe anyway, replacing the run is the better fix, and that is where a trenchless method earns its keep.

It is priced after a look at the site, and a few things move it most:

• Length and route. A long run from a meter at the property line costs more than a short one beside the house.
• What is on top. A bore under a driveway, pavers or a pool deck saves the most restoration compared with digging.
• Method. Pulling through the old pipe is usually the quicker job when the new, smaller pipe can still carry the load.
• The sewer and other lines. Locating the sewer with a camera and hand digging around crossings adds time.
• Permit and inspection. The city permit, the pressure test and the gas clearance are part of every job.

Sometimes. Southwest Gas lists a second option for customer buried piping: having the meter relocated, at the owner's expense, so that it sits next to the house. That "will greatly reduce, or even eliminate, the pipe for which you're responsible," the utility says, because the line up to the meter becomes Southwest Gas's to own and maintain. Southwest Gas takes questions on customer buried piping and meter relocation estimates at 800-654-2765. If the meter is far from the house and the old line is failing, it is worth comparing that option with replacing the line.

HQ Plumbing & Air repairs and replaces gas lines across the Phoenix area, from the meter to every appliance. We find leaks by capping every gas fixture and pressure testing the system at the meter, and when the gas has been shut off for a leak, we pull the permit, fix the leak, run the test and take it through the city inspection so Southwest Gas can turn the gas back on. If you smell gas, leave the area and call Southwest Gas at 877-860-6020 and 911 from a safe place. For a failing buried line, call us for a free estimate.