I installed a new gas line last year. I went from the meter to the
shop (70'=0"). I installed plastic underground 18" minimum depth. You
also have to lay tracer wire next to pipe before filling trench. One
possible hint that may help you, the plastic tubing has to be pushed
on the steel ell. This has to go up tight, easier said than done. I am
a fairly big guy but had problems with it. I took a short piece of
2x4, bored a hole the diameter of the tubing. Then sawed it lengthwise
to give me two halves to clamp around pipe.Then pulled from this yoke
with a 12" bar clamp. The job went easy after that.
In my area the only gas line that can be installed underground is
plastic or a certain type of copper. Steel pipe, galvanized steel is
not allowed underground.Your building code may be different than mine.