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  • CNG tank recertification

    so I found a tank seller on Ebay that states that CNG tanks can be recertified much like scuba tanks. His pictures learly show the expiration date. I sent him a message telling him that I thought tanks had to be rendered unusable once they expired. Here's his response. Comments as I'm now officially confused.

    "No, that is a common myth. I talked with the sole remaining American engineer in Wisconsin after the company sold their tooling to a Korean company and was given insight into the history behind the original 15 year certification: SCUBA tanks have to be inspected and recertified much more often due to moisture in the compressed air. This is not really an issue in methane (natural gas) but the company and federal DOT wanted some time horizon to evaluate the blanket certification without individual tank reinspection and they decided on 15 years with a proviso for blanket extension WITHOUT individual tank reinspection depending upon the tanks' performance during the initial 15 year program. They never had a failure or problem with any of their tanks in use during the initial 15 years or beyond and met every criteria for a blanket extension of the original 15 year certification without examination of individual tanks. However, to receive that blanket extension requires the original manufacturer to submit the results and application for blanket extension to DOT. But the Korean company that bought the tooling has no interest in reducing demand for its product, so it is not submitting the paperwork. Should you feel safe without an examination of every individual tank? Sure, but that's a judgment call. In any case, there is NOTHING in the original DOT certification or proviso for blanket extension that prevents anyone from re-certifying their tanks with individual inspection. Please note that my tanks have quite a long lead time built in before any reinspection could be required, so my telling you this doesn't really help my auction (some folks who thought they might need to replace their tanks will decide to keep using them) but I want to be 100% honest. Please feel free to do your own research but the idea that tanks must be destroyed after 15 years is a myth."

    Thanks,

    Jim

  • #2
    Re: CNG tank recertification

    Nowhere in DOT FMVSS 304 nor in ANSI NGV2 (the two specifications to which Pressed Steel Tanks were certified to) does it talk about a proviso for blanket extension. I have been invovled with certifying pressure vessels including CNG tanks for the past 5 years and have never heard of any composite pressure vessel having an extension beyond its expiration date. It says on the label DO NOT USE AFTER ******. I would ask for the contact info for the "sole remaining American engineer in Wisconsin", and ask to see the documentation that he has regarding this proviso for blanket extension. And the comment about no moisture in methane or CNG if wrong as well. Most compressors of CNG have driers because there is moisture in the natural gas. I wouldn't buy the tank(s). If you do buy the tank and have it inspected by a CSA certified inspector, they will condemn the tank to be destroyed because it expiration date has passed.
    Jared.
    Mountain Green, Utah
    2003 CNG Cavalier
    2003 CNG Silverado 2500HD

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    • #3
      Re: CNG tank recertification

      The difference is that SCUBA air is supposed to have moisture in it, while CNG is supposed to be dry. Not that it always is, but should be. It would be interesting to put a CNG tank through a standard hydrostatic test and interior inspection and see what they say. Anyone ever done that?
      02 GX
      01 GX
      03 Crown Vic
      06 GX
      Home Fueler

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      • #4
        Re: CNG tank recertification

        You would think someone would want to test an expired tank to destruction along the lines of the original certification requirements just to see how well they are holding up. It would be of particular interest to see if tanks whose overwrap is exposed to road debris, sunlight and dirt and corrosion are more prone to failure then tanks that are installed within the trunk of the vehicle. And if they are, how much less margin of safety is in those tanks. Also, aren't some of the new tanks certified to 20 years? I thought I read that somewhere.

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        • #5
          Re: CNG tank recertification

          I wrote that guy and offered him $50 if he could find me someone who recertifies tanks. I told him he wasn't going to find anybody because nobody recertifies tanks. Nobody wants the liability. He never got back to me. His explanation of why CNG tanks can be certified is very choppy. I don't follow his reasoning. It's too bad that whoever buys the tank won't even attempt to "recertify" until 2017, when that particular tank expires.

          I wrote him, he never got back to me.

          http://cgi.ebay.com/ebaymotors/Dual-...item414df6c102
          1998 Honda GX
          ebike

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          • #6
            Re: CNG tank recertification

            Under NFPA 52, it has to be inspected before it is installed in a different vehicle.

            I shouldn't say this but I have seen a cut-a-way type 1 tank that had been in service for over 30 years (from what I was told) and it was perfect. They wre in a "museum" at a testing facility.

            Eventhough I have seen tanks that were good, when the life has expired, I would not take the chance on using them, especially type 3 and 4

            Larrycng

            Larrycng

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            • #7
              Re: CNG tank recertification

              Well seeing how you can't recertifies & new ones cost way to much,
              Has anyone converted their Civic GX back to a gas car?

              How hard was it & how much did it cost?
              Last edited by John Mitton; 12-11-2010, 08:56 AM.

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              • #8
                Re: CNG tank recertification

                if I was going to try to convert to anything other than cng it would be propane I am not a honda guy but there are lots of them here I dont know what the rail pressure is on the honda but if it is around a 100 or so I think you should be able to run it to a vaporiser and than to the low pressure side of the high pressure regulator than you would have to figger how to trim the fuel rate as the propane has more btu this is where I would start as the compresion ratio I think is high in the honda again a honda guy question if it is than to use gasoline you would have to change the pistons or put a spacer plate under the head as we do with the cats to make them run on cng propane tanks are a lot cheaper than cng tanks for a few 100 dollars you can be the proud owner of one that is dot cert (and nooooooooooooo you cant use one for cng very bad things will happen) but this could be a very cool clean air car as propane is much dencer than cng so how far can it go 15 or 20 gallon tanks a long wayLOL and if you can convince the computer to run it at the right mix it would be way cool and I bought propane this morning for 2.12 per gallon so still cheaper tha gasoline ok honda guys tell me why it wont work or better yet why it will

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                • #9
                  Re: CNG tank recertification

                  I knew there was something I liked about you Cowboy. I think I've related this before, but a friend of mine added Lp to his factory cng dodge caravan and it worked (and drove the guy at the lp dock crazy).

                  The lp tank, vaporizor, and regulator (one with an adjusting screw) was installed and "T"ed into the cng fuel manifold with a 3 way valve. Chrysler pressue is about 110 psi (Honda is about 40 psi). Because of the heat value of fuel the lp pressure was lower than NG. We had to lie to the fuel rail pressure sensor since fuel pressure to run on lp was lower than cng and fuel trim numbers and therefore injector pulse width goes is too long. A resistor was used. As long as the computer sees the expected pressure no matter what the rail pressure is, the O2 sensor can adjust the injector pulse width and the engine will run right.

                  The problem with the cat will be improper (too rich ) fuel mixture.
                  I would love to convert a GX to LP just for fun. I filled up the Lp tank on the RV last week for 3.25 per gal in Yucca Valley -- not worth the conversion.
                  Besides, you couldn't SMOG it in CA -- but I could do it in Washington -- no SMOG where I live!

                  Larrycng

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