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Why do people buy expired tanks?

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  • #16
    Re: Why do people buy expired tanks?

    I know of some people who are purchasing expired tanks, decommissioning them safely and then selling them for scrap.
    www.CNGUtah.com

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    • #17
      Buyer beware. Used CNG vehicles being sold on eBayMotors, PublicSurplus and GovDeals often dont state that the fuel tank is expired and would cost $4000 or more to replace. Seller can find expiration date on the tank label. Those who use and trade CNG vehicles know to check for this date, but novices are likely to miss this show-stopper (vehicle not approved for use) because they may be too busy researching where to find fuel stations to decide if the car can be used in their area. Fortunately, any browser search will display posts in cngchat to alert buyer to investigate further.

      Five of the 30 or so CNG vehicles presently listed on the aforementioned websites have expired tanks which isnt stated in the listing.
      .

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      • #18
        Years ago I sold a set of CNG tanks that had about 5 years remaining on them to a guy that was developing a water propulsion system (engineering prototype). I was kinda disappointed to hear he was not installing them in a CNG powered vehicle. He needed tanks that could handle high pressure (less than 2000 PSI) and would not easily corrode and had a good volume. I was a little concerned that he might remove the valve with some residual pressure in the system so I had a chat with him about there potentially being some pressure left in the tank although they were emptied. Unbelievable that he was the high bidder on ebay as opposed to somebody needing then for a vehicle. Probably just thew out the electronic valves.

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        • #19
          Most end up in dump.
          Sold GX

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          • #20
            I also don't understand the tank expiration dates. They seem a little arbitrary. I see some tanks from the same manufacturer that could be either 15 year or lately 20 year end of life. What's the difference in the design? The manufacture won't tell you, its almost like the customer required 20 year tanks and presto, the 20 year sticker goes on. It also seems like the location of the tank should have some bearing on the life. One placed under the bed of a pickup truck exposed to the heat from the engine and the exhaust, stones, road salt and debris along with radiated heat from the road and sun would have a lot shorter life than the one in the trunk of a Honda. I just bought a CNG Impala with a type 1 tank. Why can't that tank be hydro tested? After all its just a steel cylinder similar to a dive tank or oxygen tank in construction. Why such a short 15 year life? Another point, like Murphy said about GSA cars. I bought a Cavalier from a GSA sale a few years back. With the scan tool, you can see how many miles the car has driven on gasoline and how many on CNG. The only time it ever ran on CNG was when it was built---less than 150 total miles in the life of the car! Pretty easy to have a fair idea if the tank is original. Knowing the build date of the car and the build date of the tank is a clue. You can also check the records on the vehicle to see if there was anything done during the warranty period along with looking at the tank inspection stickers. GSA cars I bought had a pretty good history of the tank inspections. So, the Cavalier had one cycle on the tank in its lifetime until I bought it. If you want CNG to become more mainstream, you need a longer tank life---20 years is acceptable for a tank and that's a better match for a vehicle's useful lifecycle. 20 tanks aren't Unicorns. They are out there. A fifteen year tank is right at the point where the vehicle is still perfectly fine but it is cost prohibitive to replace it (usually about the same value as the vehicle). So the vehicle gets scrapped. This is the same scenario that happens to EV's. Although the battery isn't thrown away when it is working perfectly, it tends to wear out late in the vehicles life leading the owner to the same place the CNG owner is---replace or scrap. I think this is why used EV's are real cheap---nobody trusts them. Back to my Impala with it's 15 year tank. Because of the delivery problems with the Impala's, my tank was manufactured in 2014. It's now 2016 and I can pretty much tell you how many cycles are on that tank. So I've lost a little over 14% of the life of the tank basically sitting in storage. It's a plain steel tank locked in the trunk, no composite questions here. In a case like this, the tanks "IN SERVICE" date should rule, not when it was manufactured. Just my two cents but I think we have a large enough database on CNG tanks to really start looking at the actual safe, useful life of these tanks not some product liability lawyer deciding that 15 years is the 400% safety factor so that no matter what you do to the tank, it will never fail.

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            • #21
              Tank manufactures do not control usage and they need to place some limitation on the tank since they do not want the liability forever. Expiration dates are the easiest thing to do since they do not control the "monitoring" of the tank after it leaves their factory. I agree that there are probably many low usage tanks that are just as safe to use at 15 years as others with much less time but higher usage or exposure. I disagree that increasing the useful life of a tank would would have much of an impact on CNG vehicle sales. I did not see any change in sales when the 20 year tanks came along. The main factors for CNG usage as a fuel have been and remain; the price differential between gasoline and CNG, the cost to outfit a vehicle, and the availability and cost of fueling. Fleet folks are the biggest users of CNG vehicles and they rarely keep a vehicle beyond 15 years. Folks like us are generally the secondary users that don't really drive the market but take advantage of good condition vehicles that were not fully utilized. Tank manufactures don't control the behavior of individuals like us but they can certainly distance themselves from indefinite liability. Kind of reminds me of a medical equipment or aerospace manufacturer using a commercial off the shelf electronic product that states it should not be use in safety critical or life saving equipment. The user takes on all liability when they use it since the manufacturer will not support those applications.

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              • #22
                I was standing at a fueling station Friday, an older Dodge van fill at a tempter compensating 3600 PSI. dispenser........

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                • #23
                  Mike, I see that occasionally too. The old Dodge vans had 3000 psi cylinders from Comdyne - which were recalled, right? Makes you want to run from the scene.

                  As for 15 yr vs 20 yr, the qualification process for NGV2 cylinders includes an ambient cycling test (liquid) of 2,250 times the service life in years. So a 15 year tank passed a 33,750 cycle test / a 20 year tank passed a 45,000 cycle test. So the manufacturer generally has to spend more on additional carbon fiber (or pay up for more durable fiber) to make a 20 year tank.

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                  • #24
                    So now I understand about the cycle thing. It looks like it works out to a little more than six cycles per day. Say my vehicle only goes 100 miles on a tank of CNG and I drive 600 miles per day (long commute, seven days a week, never a sick day). I am having to fill it 6 times to do get where I am going. 15 years is 5475 days so at six fills (cycles) per day to go 600 miles the vehicle will travel 3,285,000 miles before the tank expires. In reality, most CNG vehicles go farther than 100 miles on a tank so the total miles driven at this cycle rate would be much higher except now you are beginning to drive nearly 24 hours per day. I don't know what you would have to do to put anywhere near those kind of cycles on a tank---I don't think that even an over the road truck (because of the higher fuel usage but larger tank capacity) could do those kind of cycles. Medium and Heavy duty trucks might make the 3 million mile mark within the allotted time but cycle times most likely not. It would be interesting to poll some fleets to see what their daily cycles on short and long haul tractors are. Nobody with a passenger car or light truck is ever going to get close to these numbers in the real world. Am I missing something here or is my math wrong? I understand there needs to be life limits on something as important as a pressure vessel and I don't condone operating a vehicle with expired tanks. However, with the amount of data we have on CNG tanks over the years there must be a more realistic way to determine the actual safe lifetime of a tank when used in the service for which it was originally designed (i.e. light or heavy truck, passenger car, forklift, etc.). With modern electronics you could easily determine how many cycles a tank had on it along with percent of fill per cycle, total fuel usage, temperatures or just about anything else you need to know to optimize the life of the tank instead of going with a "one size fits all" approach. End of rant--when my current tank expires I might be too old to drive or have expired myself.

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                    • #25
                      All good points siai47.

                      Another NGV2 criteria is to cycle test one cylinder from each batch during production to 750 times the number of years on the label -- but this time up to 125% of pressure (i.e. all the way up to 4500 psi). So our theoretical NGV owner might be in a hot climate where he fills well above 4000 psi every day twice a day and still be confident that the cylinder is up to this abuse for the specified years on the label. Yes, this scenario is a stretch but a 24/7 over-the-road truck running I-10 might fall into this category.

                      If we could somehow be certain a cylinder remains on a vehicle and the fill history could be stored into nonvolatile RAM it would be possible to put cycle counts into the vehicle's computer to determine when it's time to remove the cylinder from service. But what would be uncertain is what physical abuse which it had sustained - especially for undercarriage fuel storage. It's a tough subject, and one that really has no complete answer yet.

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                      • #26
                        I have been thinking again. how about we put a red ribbon around the tank and when the tank gets to the point that it expands beyond the safe diameter when filled it would break same if over pressured and the tank would be considered condemned.

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