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Standards Division

Corrosion Issues with Underground Propane Tanks

How to meet the requirements for testing and documentation for customer-owned tanks

Summary

Underground propane tanks are a great way to store propane and not lose space in your yard or have to look at the tank.  They are also protected from the effects of fire.  But, they can rust and cause problems for their owners.

Consumers who own their own underground propane tanks need to know that some of the rules for those tanks have changed.  The rules specifically apply to new installations (as of January 1, 2011), but they can affect tanks that have been installed for several years.

The latest edition of the LP-Gas Code has a requirement that each underground (UG) propane tank installed after January 1, 2011, must have a cathodic protection system (see below) included to help prevent corrosion of the tank.  There are also requirements for testing the effectiveness of the system on a specified schedule, to document the testing, and to maintain the test results for a specified time. These requirements are not retroactive to tanks installed prior to January 1, 2011. However, if a tank is tested and fails, indicating that corrosion of the tank is actively occurring, then it must be corrected. This is usually done by adding an anode or two to bring the voltage into compliance (see below). Once this happens, the tank comes under the 2011 requirements and must be periodically tested.

Background Information

The purpose for the cathodic protection is to provide a higher level of safety.  UG propane tanks can be subject to severe corrosion conditions and can degrade and start leaking over time with no visible signs.  Leaks from UG tanks have resulted in injuries and severe property damage. 

The type of cathodic protection usually provided is an anode bag, which is a magnesium or zinc rod enclosed in a cloth bag with a moistening agent and electrically connected to the tank.  This is not the place to go into the theory of operation of a cathodic protection system, but the metal in the anode bag corrodes away and, in so doing, protects the steel of the propane tank, just as a sacrificial anode does on a boat.

Meeting these requirements for tanks owned by the propane companies is not a significant issue.  They know the requirements and have accepted the responsibility to comply.  Tanks owned by their customers are a different situation.  Testing must be performed according to the specified schedule and documentation kept.  We are trying to determine how to best accomplish that among customers who traditionally know little about the technical side of their propane systems.  However, those who have purchased their own tanks have the responsibility for performing tests or having them performed and maintaining documentation.

The schedule for testing these tanks is not burdensome, but it must be followed.  The test is conducted with a volt meter and a certain reference cell and returns a voltage value.  Above a certain voltage and the system is working properly; below that value, it fails.  The initial test must be performed when the tank is buried and verifies that the protective system is working.  The second test occurs 12 to 18 months later.  If both of these tests result in values that are acceptable, the test interval increases to not more than 36 months.  If the test value ever falls below the acceptable voltage, the system must be repaired and the test schedule starts over.  The results of each test must be documented and the results for the last two tests must be retained and available for inspection. We suggest that the test results should be kept for the life of the tank. The voltage readings can be valuable information and can indicate when the anode may be reaching the end of its life.

We are still in the process of determining how we will implement the testing process requirements for customer-owned tanks. The owner is responsible for providing the cathodic protection and for doing the required testing. However, they can make arrangements to have it done for them. The propane company maintains the test results for tanks they own. The consumer is responsible for maintaining the results for tanks they own. The questions of how an inspector can view those records and how a propane company delivery person can know the corrosion control status of an underground tank are yet to be resolved, partially because the rules do not clearly specify this.

On-Tank Notification

One company in Colorado, where testing for anodes on UG tanks has been required for several years, uses tags attached to each tank to indicate the results of the testing. The tags they use are shown below. Please DO NOT copy these tags for use to meet the new requirements. First, they are for use in Colorado, only, as the law referenced is a Colorado state law. Also, the testing interval statement is not appropriate for the new requirements. We will provide some suggested new wording shortly. More information about these tags is available in the LP-Gas Code Handbook, 2011 edition, on pages 212 and 213.

Tag that shows successful test

Front of rejection tag

Back of rejection tag

Last revised October 5, 2012.

 

NCDA&CS Standards Division, Stephen Benjamin, Director
Mailing Address:1050 Mail Service Center Raleigh, NC 27699-1050
Physical Address: 2 West Edenton Street, Raleigh, NC 27601
Phone: (919) 707-3225; FAX: (919) 715-0524