Underground Tank Installations

The 2011 edition of NFPA 58 (Liquid Petroleum Gas Code) added a code regarding dielectric fittings and their use with underground piping systems from the storage tank.

• NFPA 58 6.9.3.16
  • Underground metallic piping, tubing, or both that convey LP-Gas from a storage container shall be provided with dielectric fittings at the building to electrically isolate it from the aboveground portion of the fixed piping system that enters a building.  Such dielectric fittings shall be installed above ground and outdoors.

Typically most installers would put a dielectric or insulating union where the pipe came up from the ground and prior to a second stage regulator, vapor meter, and/or the penetration into a building.  That would satisfy the above code and everyone could move on.  However, with the emphasis in recent years on proper sizing and testing of the Cathodic Protection systems for the underground storage tank itself, the NFPA issued a Tentative Interim Amendment (TIA).

• NFPA 58 A.6.6.1(I) Paragraph 6*
  • It is important that, when a cathodic protection system is designed, there is a clear understanding of the limits of the surface area and the materials being protected.  Electrical isolation of the container from metallic piping may be necessary using a dielectric fitting or other component designed for that purpose.  For example, the cathodic system that protects a steel tank that is not electrically isolated from the attached metallic piping system will be forced to provide protection for the connected piping system as well.  Therefore, the sacrificial anode will have to be sized to protect both the container and the piping.  Additionally, if the piping is different material (such as copper) from the container, further complications could result and it is possible that the steel may corrode even though a sacrificial anode is connected to the container.

As this addition was part of a later change from the NFPA 58 Annex, it was not part of the 2011 code.  Some jurisdictions, however, follow the Annex as code and compliance are required.  Like any installation, be sure to check with your Local Jurisdiction Having Authority.

Back in 2011, in order to help adhere to the code and simplify installations, RegO introduced a line of Pigtails and Hogtails that were designed specifically for use on Underground LP-Gas containers.  The D912 & D913 Series Pigtails and Hogtails feature an Electrically Insulated POL Connection on one end and, once installed to the tanks POL service valve opening, it isolates that container from any piping system installed beyond that point.  The Pigtails are available in 12, 20, and 30inch lengths with either M. POL x M. POL or M. POL x ¼” MPT.  The Hogtails are available in 12, 20, 30, 36, 48inch length with the M. POL x M. POL ends.  When using such a pigtail, dielectric protection would still be required where the piping system comes up from the ground and prior to a second stage regulator, vapor meter, and/or the penetration into a building.

Other available dielectric fittings include female pipe thread unions, male pipe by male flare unions, and flare by pipe unions with a shut-off valve.  Be sure to contact us for any of your Dielectric Fitting needs as well as any other equipment you may require.