What the LP Gas Code says about installing, testing cathodic protection systems

Out of sight, out of mind? It may seem that way. But you need to keep underground (UG) propane tanks in mind, at least occasionally.

UG tanks generally require less maintenance because they are protected from damage and don’t show corrosion. You can’t paint them without going to a lot of trouble. Some companies along our coast bury propane tanks rather than use above-ground containers because they are better protected from corrosive salt spray. They say that an above-ground 100-pound or 123-gallon container may be too corroded to continue its use after as little as a year. UG tanks last a decade or longer. But UG tanks corrode, too, but you can’t see it.

The LP Gas Code added requirements to install and test cathodic protection (CP) systems for UG tanks in 2011. Doing so had been optional for years but became mandatory for new installations when states adopted the 2011 or later editions. Be aware, there has been a longtime requirement to protect UG tanks from corrosion, but it generally fell to the paint, phenolic resin coating or mastic coating to be the protection. These methods were not perfect at installation and got worse as time progressed. But who knew? Nobody could see the tanks rusting away underground. Sometimes the first hint was the smell of leaked propane when filling the tank. Also, other conditions, such as heavy fertilizer use and gravel touching the tank, can drastically reduce tank life to as little as six months.

I mentioned testing. The new requirements came with a specific CP testing schedule. Knowing that many dealer employees are busy, I expected a cottage industry of CP testers to spring up and offer their services to perform the testing and provide documentation. Maybe they would fix systems not performing up to snuff or inform dealers about which installations needed attention. I met someone in such a business for the first time this summer. He started his business a year ago, so my prediction came true after 13 years. He reports that the dealers he tests for are somewhat behind schedule, but he is helping them come into compliance. A dealer employee who called me wouldn’t say they were behind, but they were “making progress catching up.”

The LP Gas Code does not specify CP installation requirements or testing procedures. And I didn’t find much about installing CP systems on manufacturers’ websites. Maybe they include something with their products. The Propane Education & Research Council has installation, testing, troubleshooting and retrofit instructions in its Corrosion Prevention Instructor Toolkit. A quick review of its PowerPoint presentations gave me a good feeling about the quality of its program. I’ll be spending time on this soon. There might be some proposals to put CP installation and testing requirements in the code.

The CP testing schedule is well-defined. But how is a driver supposed to know that the UG tank about to be filled is up to date on its testing? The code does not address that in the requirements. However, there is information in the LP Gas Code Handbook that greatly expands information about CP. In Exhibit 6.30, it shows some tags designed for use in Colorado to inform the driver. The white tag shows that the CP on that tank passed and when the next test is required. A red tag indicates it did not pass the CP test and should not be filled.

What do we know about the condition of tanks where the CP system failed or had expired and was then successfully repaired? Not as much as we would like. The CP test is a snapshot of conditions at that moment. If the CP system has been insufficient for some time since the last test, the tank was corroding, but we don’t know how much. Repairing the CP system reduces corrosion activity, but a lot of damage could have happened before the fix. That’s why you should keep up with the testing and plot the results. Two test results allow you to plot a line to predict when to augment the old anodes. Three test results allow you to plot a curve that probably better predicts the demise of the CP system.

All of this applies to CP using anode bags. I haven’t even gotten started on impressed current systems. They’re not common on UG propane tanks but are regularly seen on big piping systems and multi-tank installations. But that’s a column for another day.

Richard Fredenburg is an LP gas engineer at the North Carolina Department of Agriculture and Consumer Services, Standards Division. He is also a member of NFPA’s Technical Committee on LP Gases. Contact him at richard.fredenburg@ncagr.gov or 984-236-4752.

NOTE: The opinions and viewpoints expressed herein are solely the author’s and should in no way be interpreted as those of LP Gas magazine or any of its staff members.

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