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  • #16
    Re: All about tanks

    if a 7 gge tank with a full 3600 psi charge developed a leak how long would it likely take for it to vent off? how loud is it? any clips of this kind of thing?

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    • #17
      Re: All about tanks

      a PRD is a pressure relief device. it let's the tank empty if the temperature is too high. the arson fire in Washington was not near enough to the PRD to trigger it in time, hence the 'blanket' fix.

      Steel tanks can be tested and recertified. The other types can't be recertified because there isn't a reliable way to test the integrity of the non-metallic structure.

      And, I don't want to be around to see HOW a CNG tank fails when it fails!
      02 GX
      01 GX
      03 Crown Vic
      06 GX
      Home Fueler

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      • #18
        Re: All about tanks

        Aaragorn, I don't believe that anyone's mad because you ask a question. The professional's who deal with this type of situation just get very nervous when the uninitiated tinker with the idea that they can tackle these projects on their own.

        Personally, I'm glad you asked, it gives us an opportunity to stress just how dangerous working on a cng vehicle can be, as well as trying to save money and time by using faulty, damaged, expired, or inappropriate tanks.

        Believe me when I say that you aren't the first to try and grasp the fineries of cng conversions and added tanks. It's definitely something to be left to the professionals in the field. It's also why it's so hard to get detailed info from them. It's not what you know that gets people hurt... it's what you don't know that you don't know.

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        • #19
          Re: All about tanks

          Originally posted by freedml View Post
          a PRD is a pressure relief device. it let's the tank empty if the temperature is too high. the arson fire in Washington was not near enough to the PRD to trigger it in time, hence the 'blanket' fix.

          Steel tanks can be tested and recertified. The other types can't be recertified because there isn't a reliable way to test the integrity of the non-metallic structure.

          And, I don't want to be around to see HOW a CNG tank fails when it fails!
          what's different about testing a metalic tank and a non-metalic tank? how are they tested and recertified? once done are they good for another 15 years? how do they determine how long they would trust them for?

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          • #20
            Re: All about tanks

            I could be wrong, but I suspect part of the issue with age of fiber wound tanks is, the materials become weaker or more brittle with age. Years and years ago I remember motorcycle helmet manufacturers recommending replacing your fiberglass helmet after 5 years because of this.

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            • #21
              Re: All about tanks

              I am of the opinion that the reason for the expiration date on composite overwrapped tanks (Type II, Type III, and Type IV), is because nobody really knows the "long term" effects of composite materials. Steel has been around for a long time (thousands of years). Using carbon or glass fibers as reinforcement on tanks is fairly new technology (1960s). It takes time to trust the materials. Besides the processes of fabricating a composite tank is much different than fabricating an all steel tank.
              Jared.
              Mountain Green, Utah
              2003 CNG Cavalier
              2003 CNG Silverado 2500HD

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              • #22
                Re: All about tanks

                At 3,600 psi, Lincoln Composite's 21 GGE tank has the equivelant explosive force of 7.1 pounds of TNT.
                Jared.
                Mountain Green, Utah
                2003 CNG Cavalier
                2003 CNG Silverado 2500HD

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                • #23
                  Re: All about tanks

                  Not too long ago they did rehydrotest NGV cylinders until they realized that over pressurizing cylinders is a destructive process and ruined a lot of perfectly good tanks.
                  To clarify, no NGV-2 cylinders (Types I, II, III, and IV) can currently be recertified for another 15 years.

                  There are also curtain classes of ASME pressure vessels and spheres that are also age limited and cannot be recertified.

                  It is DOT 3AAA bottles that must be recertified be hydotesting every 5 years. But they cannot be used in NGVs.

                  Hydrotesting is when they fill the tank with water, put it in a graduated cylinder of water, over-pressurize it, to see how much it expands, depressurize it and see if it contracts to it's pretest size. If it doesn't contract back, it fails and is destroyed.
                  So you can see how such a test would stretch out and destroy the integrity of any wrapped cylinder.
                  Last edited by cnghal; 06-05-2008, 03:09 PM.
                  Your Friendly Nazi Squirrel Administrator

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                  • #24
                    Re: All about tanks

                    FYI, the new NGV2 specification (NGV2-2007) now allows for tank life of 25 years on new designs.
                    Jared.
                    Mountain Green, Utah
                    2003 CNG Cavalier
                    2003 CNG Silverado 2500HD

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                    • #25
                      Re: All about tanks

                      I've been measuring the Pathfinder. Looks like the back end has about 44" width and 16" depth when the seats are in the upright position. So how big a tank would that accommodate? 16" dia. and leaving enough room for the valves on the end. How do I figure gge from these dimensions? What would a tank weight of the different types? I II III IV?

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                      • #26
                        Re: All about tanks

                        Originally posted by Highmarker View Post
                        FYI, the new NGV2 specification (NGV2-2007) now allows for tank life of 25 years on new designs.
                        if you under pressurize when filling does it extend the life? a 25 year life is likely longer than I would want to own the vehicle.

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                        • #27
                          Re: All about tanks

                          Originally posted by Highmarker View Post
                          FYI, the new NGV2 specification (NGV2-2007) now allows for tank life of 25 years on new designs.
                          While they can have a 25 yr service life, that is a function of the tank manufacturer, right? The manufacturer can set 15, 20, or even 25yrs on the expiration. I've seen 15 & 20's, I'm not aware of anyone doing 25 yrs yet. That's still a fairly new standard, do you think it may be a while before we see the 25 yr tanks available

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                          • #28
                            Re: All about tanks

                            Originally posted by Highmarker View Post
                            I am of the opinion that the reason for the expiration date on composite overwrapped tanks (Type II, Type III, and Type IV), is because nobody really knows the "long term" effects of composite materials. Steel has been around for a long time (thousands of years). Using carbon or glass fibers as reinforcement on tanks is fairly new technology (1960s). It takes time to trust the materials. Besides the processes of fabricating a composite tank is much different than fabricating an all steel tank.
                            You're right in stating that steel has been around for a much longer time, therefore it is much more clearly understood, and we have a much better understanding of what will lead to catastrophic failure (the driver killed when the owner did not have the proper safety check) versus a gradual failure. There is also a well-understood microstructure (crystallline structure of the atoms involved) upon which strength of materials estimates can be based.

                            In the case of fiber reinforcements--either glass or carbon fibers--the composite structure is strong up to a point beyond which it fails (look at the pictures from the link that is a few posts down from here--that shaggy doghair on the tanks is fiber material that has snapped out of its manufactured position.) There is no real middle ground, like a green stick from a tree has. The microstructure of the overwrap is reasonably well understood, but because we are talking about amorphous substances (--remember hearing that glass is a super-cooled liquid? That just means that it does not have an overarching microstructure--) there is more variability in the calculation of material strength.

                            Aging is a factor in both metals and composites, but that's way too much for me to think about at this late hour, much less try to explain. If yer interested, shoot me an email and I'll try. Compression/depressurization of the tank does effect the microstructure, however.
                            Last edited by Andy-Paul; 06-06-2008, 06:41 AM. Reason: extra data

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                            • #29
                              Re: All about tanks

                              So who benefited from that attack? What political agenda was behind it? I don't see how a terrorist act like this proves anything about the technology except that it can be exploited for destructive purposes like so many other things. The human factor of intention is what failed here, not the technology.

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                              • #30
                                Re: All about tanks

                                Curtis,

                                The 25 year life is new only to NGV2-2007. It was published in July 2007. I haven't seen any tanks with the new 25 year life. You are right about the manufacturer designating the life of the tank.

                                Originally posted by Curtis View Post
                                While they can have a 25 yr service life, that is a function of the tank manufacturer, right? The manufacturer can set 15, 20, or even 25yrs on the expiration. I've seen 15 & 20's, I'm not aware of anyone doing 25 yrs yet. That's still a fairly new standard, do you think it may be a while before we see the 25 yr tanks available
                                Jared.
                                Mountain Green, Utah
                                2003 CNG Cavalier
                                2003 CNG Silverado 2500HD

                                Comment

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