Do Tanks Have A 5 'hydros' Limit ?

[scubafanatic]

So I dropped by Scubatoys this afternoon, to pick up one batch of tanks and drop off a second batch of tanks (for assorted visuals/hydros) and the gentleman at the counter mentions there is a '5 hydros and you're done' limit on the maximum number of hydros tanks can go through. (it's not a Scubatoys enforced limit, but apparently from their hydro services supplier.) I doubt this is a DOT or legal requirement but perhaps this hydro shop has implemented their own strange rule ?

I'd brought by a few recently acquired galvanized steel tanks and the gentleman cautioned me to shop for recent vintage tanks, with the least number of hydros possible, so as to postpone for as many years as possible hitting this '5 hydros' limit.

Anyone else ever heard of such a thing ???

 

[JohnnyC]

Neither 3AA nor 3AL tanks have a hydrostatic testing "limit" in terms of the number of times they can be tested and certified. Fiber wrapped cylinders, both 3HMW and 3FCM have a cylinder life of 15 years, during which time they will receive 3 hydros at regular 5 year intervals. After that time they must be retired.

Certain older tanks of both the steel and aluminum variety have had other issues of various persuasions, however they are few and far between these days.

 

[MaxBottomtime]

I've had 72s with original hydro dates from the early 60s and still passed. Then again, I had some 120s that didn't pass their second hydro.

 

[cool_hardware52]

So I dropped by Scubatoys this afternoon, to pick up one batch of tanks and drop off a second batch of tanks (for assorted visuals/hydros) and the gentleman at the counter mentions there is a '5 hydros and you're done' limit on the maximum number of hydros tanks can go through. (it's not a Scubatoys enforced limit, but apparently from their hydro services supplier.) I doubt this is a DOT or legal requirement but perhaps this hydro shop has implemented their own strange rule ?

I'd brought by a few recently acquired galvanized steel tanks and the gentleman cautioned me to shop for recent vintage tanks, with the least number of hydros possible, so as to postpone for as many years as possible hitting this '5 hydros' limit.

Anyone else ever heard of such a thing ???

Hoop wrapped tanks have a finite life of 15 years with a 3 year retest IIRC. 3AA? no limit I know of. I have an O2 Supply bottle with a "birthdate" in 1924. It has a a "few" more than 5 retests. It's currently sitting in my fill station full of O2.....

Tobin

 

[scubafanatic]

I imagine Scubatoys steers a lot of hydro business to their 'supplier', so if this supplier is not afraid of antagonizing a lot of scuba tank owners, one wonders if this is the wave of the future, where all the hydro suppliers get more 'conservative' and impose a new de facto standard outside DOT regulations ?

 

[cool_hardware52]

http://www.phmsa.dot.gov/pv_obj_cac...E6711F48C0E0114726B4E0200/filename/cyl_tx.pdf

Keep in mind that for most hydro stations Scuba Tanks are a small part of their business.

I suspect there is some sort of misunderstanding in play here.

Tobin

 

[NAM001]

The only factor limiting the number of hydros you can have is the space available to put new hydro stamps

 

[guruboy]

I really really doubt the hydro shop (I know the guy at the hydro shop) told ScubaToys there is a 5 hydro limit.

Also, the hydro shop does not sell tanks, so they have nothing to gain by selling tanks, only by doing hydro testing. Someone buying a new tank (instead of doing another hydro on an old tank) would probably be bad for their business.

 

[DA Aquamaster]

As noted above composite tanks have 3 or 5 year re-qualification requirements (depending on the design) and have a 15 year life limit. The re-qualification process includes both the hydro test and a visual inspection. IF, and it's a big if, the statement was made in reference to a hop wrapped composite cylinder with a 15 year life limit and a 3 year re-qualification interval, then the statement is more or less correct. Just more or less, as skipping a few years between hydro tests won't allow you to still have a total of 5 done - the tank will still age out of service at 15 calendar years.

----

Some tank manufacturers will provide a 30 year "life span" for aluminum tanks for comparison purposes with composite tanks, but there is no legal or engineering limit applied to 3AL, 3AA tanks and no life limits are applied to exempt, or special permit all aluminum and all steel tanks used in scuba diving.

3AL aluminum tanks do have a fatigue life, but they are tested to 100,000 cycles to test pressure (5000 psi for a 3000 psi 3AL tank) so the fatigue life is somewhere above that number, and that number will be even higher with the fill pressure limited to the 3000 psi services pressure. To put that in perspective, you'd have to fill a 3AL scuba tank twice a day for 136 years to get to 100,000 fills.

There are some dive shops that refuse to fill aluminum tanks older than 20 years, but that's pretty ignorant thinking. I think in many cases it is an outgrowth of the many shops that refuse to fill aluminum tanks made prior to 1990. That is done to avoid filling 6351-T6 aluminum tanks that are prone to SLC cracks, but that date itself was arbitrary as all Luxfer aluminum tanks made after May 1988 are made from 6061-T6 aluminum, and Catalina tanks were always made of 6061-T6 aluminum regardless of age. Some shops have just extended this overly conservative rule of thumb to an even more conservative and totally non-fact based determination of a 20 year "service life" - mostly I suspect to sell more tanks.

3AA steel tanks do not have a fatigue limit and provided they are properly cared for and are not allowed to develop pits from rust, they'll last what amounts to forever, for all practical purposes, with the practical limit really being the ability to find a place to put a new test stamp every 5 years. The oldest tank I've seen come in for hydro test was a welding tank made in 1911, and it was still eligible for a plus rating.

 

[Bob DBF]

I'd be finding a different hydro facility to take my tanks for hydro, and since Scubatoys supports this by sending clients tanks to them, a new diveshop as well.


Bob