Why Gas Lines Fail: Corrosion, Age, and Soil Damage

Most homeowners never think about their gas lines — until something goes wrong. But underground and behind your walls, a quiet battle is always underway between steel pipe and the forces trying to destroy it. Understanding why gas lines fail is the first step to catching problems before they become emergencies.

1. Corrosion: the number-one killer

Corrosion destroys more residential gas lines than every other cause combined. It attacks from two directions:

Exterior corrosion starts where pipe meets soil. Moisture, salts, and soil chemistry eat through protective coatings and into the steel itself. In San Bruno’s Belle Air neighborhood — built on bay-side flatlands near sea level — the high water table keeps buried pipe in damp soil year-round, and corrosion advances far faster than on dry ground.

Interior corrosion comes from moisture and contaminants inside the pipe. Older lines without proper sediment traps accumulate scale and water at low points, corroding from within where no inspection can see it.

The defense: proper burial depth, protective sleeving, corrosion-resistant materials, and — critically — pressure testing every few years to catch thinning pipe before it pinholes.

2. Age: steel has a service life

Residential steel gas pipe installed in the 1940s–60s is now 60–80 years old — well past what its manufacturers expected. Mills Park’s 1940s bungalows and Rollingwood’s 1950s ranches are full of original lines still in service. Some are fine. Many are living on borrowed time.

Aging shows up as: threaded joints that develop micro-leaks, pipe walls thinned by decades of corrosion, and materials (like old-style connectors and sealants) that modern codes long ago replaced. Age alone doesn’t condemn a line — a pressure test gives you the actual verdict — but age plus any other stressor is when failures cluster.

3. Soil movement: the hillside problem

San Bruno runs from bay flatlands to 700-foot ridges, and soil never sits perfectly still. On the steep slopes of Crestmoor and Portola Highlands, seasonal soil creep pulls buried pipe downhill — slowly, relentlessly, stressing every rigid joint. The failure point is almost always the house entry: where the buried lateral meets the above-ground riser, two movement regimes collide.

Earthquakes compress decades of this stress into seconds. Even moderate shaking can open joints in lines that were already marginal — which is why a post-quake pressure test is standard practice after any significant seismic event.

4. Poor installation and unpermitted work

Not every gas line was installed well. We regularly find: undersized pipe starving modern appliances, missing sediment traps, unsupported runs, pipe routed through framing without protection plates, and — the most dangerous — unpermitted work done without pressure testing or inspection. A line that was never tested was never verified.

This is also why every installation and replacement we perform ends with a pressure test and city inspection. The permit isn’t bureaucracy; it’s the independent verification that the work is safe.

5. Appliance-driven overload

Sometimes the pipe is fine and the demand changed. A line sized in 1960 for a furnace and a stove now feeds a 48-inch range, a dryer, and a tankless water heater — and something has to give. Starved appliances malfunction: error codes, weak flames, pilots that won’t stay lit. The fix isn’t a bigger appliance; it’s a properly resized line.

---

The bottom line: gas lines fail from corrosion, age, soil movement, bad installation, and changed demand — usually a combination. None of these announce themselves loudly, which is why proactive testing beats reactive repair every time.

Concerned about your lines? Call (833) 713-2101 for a pressure test and safety inspection. We’ll show you exactly what condition your system is in — and if you smell gas or suspect a leak right now, learn the warning signs and call us immediately.