Aluminum Hydro Problem

[wedivebc]

http://www.keynoter.com/articles/2004/08/06/news/news17.txt
is for the FL incident. From what I know, there actually was oxygen involved, & not just the usual bad reporting where air = oxygen to those bonehead reporters.
.

Actually I was aware of that from a DS thread. I am still unaware of an actual failure of a steel tank other than the one I mentioned earlier

Actually, having your tanks hydroed could well be the reason for the steady rate of failures. Pumping the critters up to 3x their working pressure can put a strain on the things.

In Canada we only hyrdo them to 5/3rds working pressure. Do you do it differently?

 

[scubapro50]

i have read about a AL tank exploding durning a fill .... but it had been painted and heat cured in a auto body shop which changed the condition of the metal .................. read about it years ago in SKIN DIVER MAGAZINE warning divers not to paint tanks then bake them

 

[Ontario Diver]

In Canada we only hyrdo them to 5/3rds working pressure. Do you do it differently?

Standard hydro test pressure in Canada is 3/2's not 5/3s. Some old cylinders that were manufactured under special permits are still 5/3s but they are rare.

Here is the standard for steel:
6.11 Hydrostatic Test
6.11.1
Each container shall be tested hydrostatically to its test pressure and have its volumetric expansion
measured. The test pressure shall be as follows:
(a) for cylinders with service pressure less than 3.5 MPa, the greater of
(i) 3.1 MPa; or
(ii) 2 times service pressure;
(b) for cylinders with service pressure equal to or greater than 3.5 MPa, the greater of
(i) 7.0 MPa; or
(ii) 1.5 times service pressure; and
(c) for tubes, 1.5 times service pressure.

Aluminum is similar

7.10 Hydrostatic Test
7.10.1
Each cylinder shall be tested hydrostatically to its test pressure and have its volumetric expansion
measured. The permanent volumetric expansion shall not exceed 6% of the total expansion at test
pressure. The test pressure shall be as follows:
(a) for cylinders with service pressure less than 3.5 MPa, the greater of
(i) 3.1 MPa; or
(ii) 2 times service pressure; and
(b) for cylinders with service pressure equal to or greater than 3.5 MPa, the greater of
(i) 7.0 MPa; or
(ii) 1.5 times service pressure.

 

[wedivebc]

Standard hydro test pressure in Canada is 3/2's not 5/3s. Some old cylinders that were manufactured under special permits are still 5/3s but they are rare.

Here is the standard for steel:
6.11 Hydrostatic Test
6.11.1
Each container shall be tested hydrostatically to its test pressure and have its volumetric expansion
measured. The test pressure shall be as follows:
(a) for cylinders with service pressure less than 3.5 MPa, the greater of
(i) 3.1 MPa; or
(ii) 2 times service pressure;
(b) for cylinders with service pressure equal to or greater than 3.5 MPa, the greater of
(i) 7.0 MPa; or
(ii) 1.5 times service pressure; and
(c) for tubes, 1.5 times service pressure.

Aluminum is similar

7.10 Hydrostatic Test
7.10.1
Each cylinder shall be tested hydrostatically to its test pressure and have its volumetric expansion
measured. The permanent volumetric expansion shall not exceed 6% of the total expansion at test
pressure. The test pressure shall be as follows:
(a) for cylinders with service pressure less than 3.5 MPa, the greater of
(i) 3.1 MPa; or
(ii) 2 times service pressure; and
(b) for cylinders with service pressure equal to or greater than 3.5 MPa, the greater of
(i) 7.0 MPa; or
(ii) 1.5 times service pressure.

Where did you get that info from? I just picked up some tanks yesterday and the operator there told me he tested tanks to 5/3rds working pressure.

 

[jbd]

Where did you get that info from? I just picked up some tanks yesterday and the operator there told me he tested tanks to 5/3rds working pressure.

Proably from Transport Canada. In the USA that info is from the Dept of Transportation(DOT). In the USA the hydro is done to 5/3 of service pressure rating. There are some tanks though that are done to 3 halves of service pressure.

 

[jbd]

Yah, the latest US fatality was from a steel HP bottle, happened last month in FL.

That being said, ALL aluminum tanks will fail if they get enough fill cycles.
Fortunately they're engineered to handle a minimum of 10,000 cycles, so a person would have to be doing a heck of a lot of diving to reach the magic number.

Notes from my recent PSI class indicate 100,000 fills to service pressure and 10,000 fills to hydro pressure for aluminum tanks.

 

[jbd]

I'd say for you're lucky to get even half that time out of an Al tank is good. I'm hoping to get 5yrs out of my Al tanks, and will switch to steel.

With proper care you should get far more than 5 years out of aluminum tanks. Same with steel tanks.

 

[jbd]

Better dive shops test ALL aluminum tanks with these devices when visually inspecting tanks. If they aren't, they are running a huge risk.

The eddy current devices are intended to be used on the 6351 alloy and not the 6061 alloy. Such a device can cause a perfectly good 6061 tank to be condemned. Even Luxfer says the eddy current shouldn't be done on its 6061 alloy tanks.

I'm willing to bet those who are saying the tanks must be condemned simply don't have the propper equipment to test them.

In some cases its not a matter of testing the tanks. There are expired permits that require certain tanks to be condemned and removed from service.

 

[SCUBAMedicBill]

Both passed hydro 1 1/2 years ago, but one failed VIP with neck fractures. Probably from sustained loads (wasn't always good about knocking down the pressure during off seasons). Bought them 27 years ago, don't think I lost anything on them. Lets see how long the second one lasts.

Bill

 

[padiscubapro]

Both passed hydro 1 1/2 years ago, but one failed VIP with neck fractures. Probably from sustained loads (wasn't always good about knocking down the pressure during off seasons). Bought them 27 years ago, don't think I lost anything on them. Lets see how long the second one lasts.

Bill

Bill,
an important note.. When storing al cylinders they should eithe be stored near empty or full never somehwere in between..

Why you may ask?? Aluminum is very effected by heat, in the event of a fire, the tank may heat up enough to allow the tank to rupture without causing the burst disk to go..
A full tank will usually have the burst disk go due to the heating of the gas.