Good question. That's something that I was wondering about at the WWCC officers' meeting on Friday. One of the concerns was a person putting 4500 PSI in a 3000PSI bottle, which is why the club's proposed HPA rules restrict everyone to 3000 PSI. However, I'm still not very clear about why we can't use fiber-wrapped bottles in boats. BTW, on the whole "fiber-wrapped bottles dissolve in water" thing, I heard some interesting clarification on that. fiber-wrapped bottles are not used in SALTwater, but fresh water is OK. Apparently the salt water permeates between the fiber and the aluminum, causing corrosion. The corrosion is thicker than the aluminum, which eventually causes the carbon-fiber reinforcement to burst, removing the primary pressure-holding element from the bottle itself. Then BOOM the whole thing lets go. But apparently that only happens in salt water, not fresh water. So as long as we're in fresh water, we should be OK. Just don't go sinking each other in the middle of the Pacific, OK?
The primary argument for at least temporarily restricting RC warship combat HPA tanks to non-composite-wrapped, all metal versions, is that there is no data available for the expected lifespan of the wrapping under the conditions present in our hobby/sport. There has been no independent testing done to determine whether our conditions, with the real possibility of direct hard hits from ball bearing rounds, might shorten the lifespan of composite-wrapped tanks as DOT has currently determined based on other types of use. Until there is data on this, it seems reasonable to hold off on using these tanks. Rob
Has any of that testing been done on metal tanks? Is there a link to it anywhere, it would be interesting to see how those tanks stand up to BB and larger impacts.
Well, there's one nice shiny round *dent* in my 48ci aluminum HPA bottle. It's even shallower than the DOT serial number and information stamp in the side, so I'm not hugely worried. An analysis of the plans provided by Princess Leia demonstrated a weakness in my battleship. The target was balsa-shielded, but by using 1/4" torpedoes, a small cruiser was able to score a direct hit. As you can see, since I'm still here, it did NOT trigger a chain-reaction and destroy my ship I'd like to trust the fiber-wrapped bottles, especially considering the abuse they regularly face in paintball and firefighting use. But in those conditions, the bottles are almost always protected by a padded cover sleeve, which distributes the shock of impact over a larger area than a bb or ball bearing. The risk that the fiber wrapping might crack or otherwise fail when shot during combat is unknown, and frankly I'd rather not find out the hard way. Aluminum bottles, on the other hand, have their DOT serial numbers stamped in them, and they survive that just fine.
The problem with that assumption is that there may be extra material where the stamp is, similar to some of the CO2 bottles I have, which have extra material where the stamp is located. Without knowing where and how the cross section of the tank varies, there is no way to know if the dent is comparable to the stamped numbers. If the stamp and hit are in the same area, it is probable that the wall is the same thickness in these areas and I would possibly make a similar assumption. If the dent is anywhere near a change in the cylinder cross section, I would be more worried, as those areas tend to concentrate stress anyways. The other thing to remember is that just because they didn't fail immediately when dented, doesn't mean that they won't fail later. Fatigue and creep are nasty phenomena particularly in aluminum. All of that is why, barring access to detailed drawings and or the analysis done during design and testing, my own personal opinion is that any high pressure vessel, be it co2 or HPA should be immediately retired and rendered unable to hold pressure should there be any evidence of damage due to impact.
As I keep getting reminded at work... There is a big difference between CO and CO2. CO is nasty stuff - fatal at fairly low concentrations because it binds very tightly with hemoglobun so we fail to absorb O2. It is the by product of incomplete combustion. Public health warning: Don't use your grill or camp stove in the house. (yeah, some people keep trying this...) CO2 is what we put out as a by-product of breathing and what plants use for their growth cycle. It is fairly low on the list of things that are harmful to the environment. With out it, we would shortly be out of plant life.
Do any of the rule sets currently require annual or regular hydro-testing of refillable tanks? If I remember correctly from my paintball days, most insured fields won't refill any tank (CO2 or HPA) that hasn't been hydro tested within 3 years. I agree with Greg that a single dent can cause a stress concentration that can limit the life of the tank, but hydro testing can re-establish a safety margin.
Almost all of the tanks Ive seen used are exempted from the hydro testing rules since they are 2" or less in diameter. That said its probably still a good idea to get one tested or just replace the tank every 5 years or so.
Hydro testing is mandated by regulation (legal regulation, not ours) on tanks larger than 2" in diameter and less than 2 feet long, those smaller than that are not tested. Part of a good inspection is a check for sevear rust, dents and deformation, any of these disqualify a tank for testing. Pressure testing does not in any case re-establish a safety margin. Hydro testing verifies that the tank is not likely to explode or fail, assuming no yielding of the tank during the test, but due to the stresses that are allowed in that test, it will SIGNIFICANTLY reduce the overall life of the tank, had it not been done. Hence the relatively frequent re-testing (and the high pressure of the test) to attempt to ensure that the tank will fail when being tested and not in the field. So in closing, no, having your tank tested with a dent does not make it safe again. Any reputable testing shop will deny you certification for a damaged tank.
Yes, my intent was that any tank in question should be sent for testing. A damaged tank should not be re-certified by a DOT licensed vendor, thus a re-certified tank should be considered safe.
