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Rusty CNG tank

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  • Rusty CNG tank

    Found a used CNG tank that looks to be out of a Contour. It's a 3000psi with a 2013 expiration date. Some of the paint has come off either due to handling and it getting scratched off or due to it's age. Most of the missing paint is aound the neck guard... about 2" down and almost all the way around. Then there are a couple other spots here and there... those appear to be from scratching. Those spots are now rusty. if I sand the rusty spots down it comes right off and is shiny.

    Should I clean it up, paint the bare spots and use it or is this an explosion waiting to happen?

    It looks like it was dragged as it's scratched quite a bit but I have to imagine these things are built like 'tanks'... no pun intended


  • #2
    Re: Rusty CNG tank

    Hello Scott,

    Cylinders are divided into 4 categories. Type 1 is all steel (or alum.) and light corrosion can be cleaned and repainted. Scratches are potentially a bigger problem. Anything deeper than .010" (not much), you should contact the manufacturer.

    If it's out of a Contour, it's probably a Type 2 with a fiberglass wrap around the center section, but the same specs apply.

    If you want more detailed information the best source is the Compressed Gas
    Association's phamplet no. C-6.4, Methods for Visual Inspection of Natural Gas Vehicle Fuel Containers and Their Installations, 2nd edition.

    Hope this helps.




    • #3
      Re: Rusty CNG tank

      Hi Afvman,

      Yes that is very helpful.

      The tank is a type II with the wrapped composite around the center. It states NGV2-2 on the tank.

      The scratches in the steel (it's not aluminum) are not deep; just enough to remove the paint and let moisture get on there.

      The scratches in the composite look to me like someone dragged it out of a truck bed. They too are not deep... maybe enough to get your fingernail caught on but not deep gouging.

      My concern was if this vessel was left out in the elements its integrity may have been compromised but from the sounds of it, a good clean up, some rust prevention and I should be good to go, huh?


      • #4
        Re: Rusty CNG tank


        Sounds like it, but...

        Any time a cylinder is moved from one vehicle to another you should/must have it inspected by a certified cylinder inspector. See:

        Here's a site that may help with the rust. State Industrial has a product called 'Converter Coat' that a lot of body shops use. See:

        Don't use a grinder. Sand or wire bursh. Unless the rust depth goes beyond 25% of the wall thickness (a lot), it'll probably pass inspection.

        Good luck,