Underground gas. Episode twenty one of Gas Service Animated. The service line between the street and the meter, the line you cannot see.

Between the main in the street and the building, the gas line disappears underground. Buried gas piping needs at least twelve inches of cover. Where external damage to the pipe is likely, the cover increases to eighteen inches. And where twelve inches simply cannot be provided, the pipe is installed in conduit or bridged to shield it. The trench matters too. The pipe rests on firm, continuous bearing, and the backfill is placed so it cannot damage the pipe.

What is the buried pipe made of? Most modern service lines are polyethylene plastic, flexible, rust proof, and joined by heat fusion. Remember episode nineteen, polyethylene lives underground only, never above grade. Coated steel is the metallic option. But a locator cannot detect plastic, so the code requires a tracer wire, an electrically continuous, corrosion resistant wire buried with the plastic pipe. One end stays accessible above ground at the building wall or riser, so a locator can follow the line.

Plastic must become metal before it surfaces. That is the job of the anodeless riser, an assembly of steel cased plastic pipe that makes the transition from plastic underground to metallic pipe above grade. Factory assembled risers are leak tested by the manufacturer. Field assembled risers use certified service head adapters with qualified instructions. And where the line emerges, it is protected against damage and corrosion.

Steel underground has a patient enemy, corrosion. It works invisibly, year after year, until the pipe wall is gone. So buried metallic piping is protected with coatings, with cathodic protection, or both. Keep the chemistry simple. A sacrificial anode is a more active metal connected to the pipe. It corrodes first, on purpose, so the steel does not. And protection is not fit and forget. Systems are tested on a schedule to prove they work.

Excavation damage is one of the leading causes of pipeline emergencies, a shovel or an auger finding a line that nobody located. So before any digging, contact the national call before you dig number, eight one one. Wait for the utilities to mark their lines, yellow means gas. Then dig carefully by hand near the marks. This is universal practice, and in every state it is the law.

An underground leak leaves clues on the surface. A strip of dead or dying vegetation along the pipe path. Bubbles rising through puddles or wet soil after rain. And gas odor outdoors with no obvious source. Remember episode six. Gas migrates underground, so technicians drive bar holes and trace the leakage perimeter to find the source.

On a service call the buried line is checked from above. Records and locates confirm the depth and the routing. The tracer wire is accessible at the riser and electrically continuous. The riser is protected and free of corrosion at grade. And nothing has been built over the line, because piping under a building needs an approved conduit.

Underground gas. Twelve inches of cover, deeper where damage is likely. Plastic carries a tracer wire and surfaces through an anodeless riser. Steel gets coatings and cathodic protection. And nobody digs until the lines are marked. Next time, pipe through buildings.