Tank Life Span

[diver 85]

Is there a limit to the number of times a tank can be Hydro'd?
I have a set of tanks that look (to me) like they are in pristene condition with shiney clean almost new valves. They just happen to have quite a few hydro stickers on them and another novice mentioned that they may not be good for much longer seeing as they can only have a certain number of inspections.
This sounds rediculous to me as long as they pass all inspections, but what do I know...

If they're Al(80's), it ultimately depends on if they were built before (8 or 9 of) '88.......Bring them in to your LDS, they'll tell you yea or ney......

 

[Hallmac]

There is no limit to the amount of retests a 3AA or 3Al may under go. I just finished two 1946 steels that while approaching the limits, they were still acceptable and returned to service.

Unless there is an exemption that directly indicates a life expectancy, then none exists.

 

[mike_s]

If they're Al(80's), it ultimately depends on if they were built before (8 or 9 of) '88.......Bring them in to your LDS, they'll tell you yea or ney......

Actually AL80's made before 88 or 89 are perfectly fine to use, even if they are AL 6351 Alloy, they just require special inspection procedures set forth by DOT. Many people still safely use these tanks....

However, with that being said, you find some dive shops that won't fill them, especially if they aren't the dive shop that inspected the tank. This is very true in "tourist dive locations" such as coastal Florida or the Keys where many of the people who dive there have driven in from out of town and the dive shop doing their fill isn't their LDS and didn't do the VIP inspection.


So... they are fine to use, but because of the limitations of getting fills, you people "put them out of service" by simply not using them anymore.

 

[low_ridah10]

I've personally seen some steel tanks in a cascade dated around this time, so they do exist.

Chris

We have some cascades from 1920's and they are still like new.

 

[ClayJar]

There is indeed a limit to the number of hydros a tank can have. The limit is that the hydro stamp must be at least one inch (IIRC) above the break of the shoulder (on newer tanks, that's usually equivalent to "at or above the level of the lowest line of the original stamping").

Since there is a finite amount of space available in that area, there is a theoretical maximum number of valid hydros (as any overstamping is cause to condemn the cylinder). Of course, since you can wait an arbitrary period between hydros (assuming the cylinder is not in service), you could have an indefinite life span with respect to time, however, the life span with respect to hydros is finite.

(Of course, for all practical purposes, cylinder life span with respect to hydro stamping area is virtually indistinguishable from infinite, but if you and your heirs care for the cylinder with meticulous precision, always cleaning and drying it and perhaps even grossly underfilling it [just to be safe], there *could* come a time when they or their descendents find that their perfectly fine cylinder can no longer be hydro stamped. I don't see that as a significant problem. )

 

[captain]

Back in the 80's I saw a cascade cylinder that had an 1898 (this is not a typo) original date and stamps every 5 years since the original. It's probably still out there, still in use.