Old gas piping failed a pressure test. When to repair joints and when to repipe the house

The City of Alexandria, Va., reprints the code's test rules for its inspectors. Piping is filled with air or inert gas, never oxygen, to at least 1.5 times working pressure and no less than 3 psig, and in a single-family house it must hold for at least 10 minutes. A gauge's full scale may not top five times the test pressure, so a 100 psi gauge is too coarse for a 3 psig test. Appliances rated below the test pressure come off the line first.

Any drop counts as a leak unless something else, such as falling temperature, explains it. Leaks are traced with a gas detector or noncorrosive leak-detection fluid, never a flame, and the affected portion is repaired or replaced and retested. A failed test proves gas escapes somewhere. It does not say how much pipe has to go.

On century-old threaded pipe, joints are the usual suspects. Jack Berleth & Sons, a plumbing firm in Huntington, N.Y., says most leaks it finds are at old tee-handle valves with dried-out stem seals or at joints where old pipe dope has gone hard and split. Its fix: take the pipe apart from the end of the run back to the bad joint, reseal, reassemble and retest. That makes sense when a few reachable joints bubble. When nearly every joint leaks, the pipe is corroded or runs sit inside finished walls, weigh the labor for each joint against a quote for new pipe. Ask for the test pressure, duration, gauge range and a list of every leak.

If the house is repiped in corrugated stainless steel tubing (CSST), which the International Code Council says needs fewer fittings, the yellow-jacketed kind must be bonded to the grounding electrode system with at least 6 AWG copper, no longer than 75 feet, clamped to rigid pipe or a fitting and never to the tubing. Black arc-resistant CSST marked AR skips that bond under the 2018 and 2021 codes unless yellow CSST is also present. Adding any yellow CSST to an old steel system means bonding the whole system.