What Happens When Your CNG Tanks Expire?

Industry experts continue to explore options for possible CNG tank recertification, as well as safer tank disposal, a federal CNG vehicle registration system, and government grant help.

August 2013, - WebXclusive

by Cheryl Knight - Also by this author

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"Appearances can be deceiving," Yborra noted. "Certified cylinder inspectors are trained to look for bracket wear, gouges from road debris, and  less obvious to the naked eye  corrosion that could compromise a cylinder's integrity." He cited examples of battery acid, industrial solvents, and other chemicals that may have been stored in the vehicle or splashed from a road spill.

Yborra also pointed out no official tracking systems are available to ensure all CNG cylinders undergo proper periodic safety inspections or are retired at set ­expiration dates.

"We feel the mechanisms the industry has in place are good  we have the right steps in place  but we don't have a way to make sure everyone follows those steps," Yborra said.

One challenge is the lack of a  national database of all CNG vehicles, whether OEM-built or converted. "Each state has its own vehicle registration requirements and only a few record fuel type," said Yborra. 
Armed with a more complete and accurate CNG vehicle registration database, he feels the industry could be more proactive, educating NGV owners about proper cylinder safety practices and issuing notices for older vehicles equipped with soon-to-expire cylinders.

The NGV industry is also addressing whether retired NGV cylinders are properly defueled and rendered unusable, according to Yborra.

"CNG cylinders are fairly expensive. We suspect that some expired cylinders are being resold by unscrupulous shops, which could result in a dangerous situation," said Yborra. He added that the resale of unexpired cylinders removed from a vehicle, while legal, should always include a thorough inspection by a certified inspector.

CVEF Task Force to Address Expiration & Other Issues

CVEF is currently assembling a task force of cylinder manufacturers, fleet operators, state motor vehicle agencies (MVA), and other government agencies to address cylinder expiration, replacement, and ­related issues.

"The task force is an extension of our current role managing cylinder incident investigations," said CVEF president Doug Horne. The task force hopes to assemble NGV inventory data  and through extrapolation, CNG cylinder data  from state motor vehicle registration databases, OEM sales data, and conversion company records. With this information, Horne's organization will contact fleets with vehicles in which cylinders are nearing the end of useful life to determine fleets' needs.

Horne suggested the task force will review potential business models to offer funding and/or leasing options for CNG tanks as well as consult grant agencies about adding CNG tank replacement to their grants.

"We'll also be looking at how to effectively move forward," Horne explained. Future plans may include discussion of a potential national NGV registration database capturing CNG cylinder information, if state MVAs cooperate.

California University Faces Wave of Tank Expirations

Richard Battersby, director of fleet services for the University of California, Davis, operates a fleet of about 1,000 vehicles and trailers; 63 are dedicated CNG on-campus vehicles, including 51 transit busses operated by the campus UNITRANS program. The campus also operates 31 bi-fuel vehicles, capable of running on either CNG or gasoline.

The University's dedicated CNG vehicles are used for general transportation, full-scale transit bus operations, utility vehicles, and on-campus maintenance vehicles.

"We have a CNG-powered refuse vehicle on order and are exploring a CNG-powered disabled access transportation vehicle as well," Battersby said.

265,000 gallon equivalents of CNG, which eliminates about 475 tons of greenhouse gas emissions each year versus operating on gasoline. "CNG provides substantial reductions in pollutants and greenhouse gases, and typically offers a substantial cost savings as well, although this can vary based upon market fluctuations," Battersby said.

The University currently pays less than $1.50 per GGE of CNG, a substantial cost savings. The University is also eligible to take a federal credit of 50 cents per GGE.

Most of the University's CNG vehicles are 1997 or newer models, but some of these vehicles will hit CNG cylinder expiration in 2011 or 2012. While the University has disposed of CNG vehicles prior to expiration date, it is now considering replacing CNG tanks on existing vehicles if proven cost effective to retain vehicles up to or beyond expiration dates.


  1. 1. Gordon Botts [ August 25, 2013 @ 04:46AM ]

    This a great article about a subject that all of us in the repair industry are not well informed about.

  2. 2. Jay Duca [ September 04, 2013 @ 07:59AM ]

    In the article it states “a variety of community colleges and other organizations provide training”. Is there a source for this training that you are aware of and is the training certified by the NHTSA? If there is a source for the training could you please list it for me?

    Thank you
    Jay Duca

  3. 3. Wilfredo Rivas [ April 21, 2015 @ 04:47PM ]

    I bought a 2012 Honda Civic in August 2013. Where can I bring the car so I can see if the gas tank has the correct amount of pressure to contain the natural gas that powers it?
    I live in Los Angeles in California by the way.

  4. 4. william sadler [ August 11, 2015 @ 12:57PM ]

    All this is B/S with the org. question. what to do with old tanks , expired tanks. You have not answered the question. If you auction them off you are giving someone else the problem with bad tanks. Who do you dispose the tanks to, THAT IS THE QUESTION.

  5. 5. Destiny [ January 22, 2018 @ 10:09AM ]

    We are in the forklift industry. I have came across an older CNG tank that I would like to get rid of. How would I go about doing that and what is the best route to take?


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