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Why are CNG tanks not re-hydrotesed or re-certified?

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  • Why are CNG tanks not re-hydrotesed or re-certified?

    Jared.
    Mountain Green, Utah
    2003 CNG Cavalier
    2003 CNG Silverado 2500HD

  • #2
    Re: Why are CNG tanks not re-hydrotesed or re-certified?

    Well said Jared!
    Last edited by John Mitton; 11-27-2013, 08:35 AM. Reason: removed long quote from opening post

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    • #3
      Re: Why are CNG tanks not re-hydrotesed or re-certified?

      The technical explanation is sound. The true crossroads will be whether users abide by the expiration or continue to drive on them. My guess is the latter, since many in this seem to be in it for total cost of ownership, at all costs, as it were...

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      • #4
        Re: Why are CNG tanks not re-hydrotesed or re-certified?

        Okay that clears it up for me. Still don't like the fact that my van 2001 Dodge has only 81,000 miles on it and the tank,s still look new but they need to be change 5/2015.

        Jared when you have a safety inspection in Utah do they check the tank expiration date,s. ??

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        • #5
          Re: Why are CNG tanks not re-hydrotesed or re-certified?

          Originally posted by amoparacer View Post
          Still don't like the fact that my van 2001 Dodge has only 81,000 miles on it and the tank,s still look new but they need to be change 5/2015.
          No one knows the history of their tank(s). You don't know if the previous owner of your van removed the tank from the van and installed it on another vehicle only to reinstall it back on the van prior to resale. The sad thing is that odometers and speedometer clusters can be changed and tampered with (I'm not saying that your van has more miles than 81,000 on it). You don't know the history of your tank. Tanks may look new after 15 years of service, and that is a good thing because you know that your tank has seen zero to minimal exterior damage or deterioration. However, the fatigue on your tank from use (pressurizing and depressurizing over and over again and again) is what will cause your tank to fail (assuming there is no external damage). And that kind of fatigue is not visible on the outside and even if you can inspect the inside of the tank, it is very hard to detect until failure occurs.

          Originally posted by amoparacer View Post
          Jared when you have a safety inspection in Utah do they check the tank expiration date,s. ??
          When I perform a tank inspection, the first thing I check is the expiration date. If that date has passed, then my inspection is done and the tank fails the inspection. In Utah, I would have to say that most shops that do the vehicle safety inspection check the tank expiration date either by themselves or through the inspection report from the tank inspector.
          Jared.
          Mountain Green, Utah
          2003 CNG Cavalier
          2003 CNG Silverado 2500HD

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          • #6
            Re: Why are CNG tanks not re-hydrotesed or re-certified?

            I have a question about DOT tank differences between DOT tanks in vehicles and in stationary use.

            If a DOT tank requires a physical inspection every 3 years (36,000 miles) when in use in a vehicle, what reasoning is there for hydo-testing a DOT tank used in a stationary setting?

            Is a stationary tank classified as a 3AA vs a vehicle tank is NGV2 the difference?

            I know of a manual fast fill module with DOT tanks in use and the question of hydo-testing came up. He was under the impression of it having ASME tanks when purchasing it. (eBay honesty)

            The module is only filled to 3600 psi temp compensated. I really wonder what the extra standard is? Are the tanks to a lower metal quality as used in the 3AA tanks as stated above? (disassembly of the module and transporting the tanks to a test station and vice versa would be a royal pain, especially every 3 years.

            Would replacing the tanks with NGV2 tanks be an option? (maybe too expensive) Then they would only require physical inspections. ASME tanks would surely be cost prohibitive.

            Thoughts? Guidance?

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            • #7
              Re: Why are CNG tanks not re-hydrotesed or re-certified?

              There are people on this board that are far more knolagable about fuel systems than me. On modern NGV system the tanks used are NGVII, DOT cylinders are used for transporting compressed natural gas not used as motor fuel. Although 3AA tanks were used on vehicles from the 70's to the very early 90's to the best of my knowlage they are only used as temporary ground storage in commercial stations. In Ca. Only ASME tanks are to be used for percent ground storage.
              Last edited by cngmike; 03-10-2014, 07:32 PM.

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              • #8
                Re: Why are CNG tanks not re-hydrotesed or re-certified?

                Use of ASME in ground storage is an OSHA requirements in most states.

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                • #9
                  Re: Why are CNG tanks not re-hydrotesed or re-certified?

                  dot tanks are every 5 years and if you keep the water out last almost forever

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