Underground propane tanks and piping are subject to electrolysis. The electrical current which occurs naturally in the earth acts as a tiny drill on an unprotected tank. The current will literally drill a hole in the tank wall, rendering your underground propane storage tank useless. One protective measure that helps prevent damage by electrolysis is the attachment of a magnesium anode bag to the tank itself. The anode bag releases electrons which protect the tank from electrolysis and corrosion.
Backfill - Covering the Tank
Although propane tanks are made of steel, buried tanks are in constant contact with moisture and other elements in an environment that is harsher than that of an above ground gas tank. Ensuring that the integrity of the ASME vessel is not compromised, the hole and tank should be covered with earth or fill that is free of rocks or abrasive materials. We recommend masonry sand as a safe material for backfill. Rocks or abrasives that are in contact with the tank will shorten the useful life of the LPG tank. Tank size is obviously a factor in determining the amount of backfill required for an underground installation. The following figures are for masonry sand:
- 250 gallon tank - 5 yards
- 500 gallon tank - 7 to 8 yards
- 1000 gallon tank - 13 to 14 yards
*Please know that tanks covered with unapproved backfill (per NFPA 58) constitute an illegal installation and are unfit for LP gas service.
When steel pipe is used as the gas service supply line in conjunction with an in ground tank, protective measures similar to those for underground LPG tanks are required. To protect the buried gas line, the pipe is required to be wrapped with protective tape. This will keep the pipe safe from any contact with abrasive material. Additionally, a dielectric union is required to be installed at the regulator to protect any transfer of current. Dielectric unions are required for steel pipe and copper tubing.
Regulators on underground tanks are required to be vented to the area above the water level in the event flooding occurs under the dome. This requires an additional vent pipe or tube to be attached to the vent of the regulator.