Aluminium Cylinders: When to destroy?

[MattDuke]

Hi,

One of my stage tanks is now 10 years old, last hydro/clean was 12 months ago.

I was advised by a few friends that once the cylinder reaches 10 years old, I would be best destroying it, as aluminium can quickly form dangerous cracking, even if it has recently been tested.

Our club has had two catastrophic failures of tanks over the last 15 years. Both aluminium, both "in test", both old cylinders. One failed during filling, and it destroyed a portion of the compressor room roof. One failed hours after filling, in a members garage, destroying part of the wall and significantly damaging his car.

I have been aware of a few things on Alu tanks, since I started diving in 1992.

My tank is a luxfor, but the alloy type is not effected by these documented stress fractures:

http://www.divernet.com/news/items/luxfer050500.htm

http://lists.drogon.net/scuba-uk-ndg/archive/scuba-uk/2000/q1/msg01333.html


So therefore, we are just back to having a standard alu cylinder that is 10 years old, and made from the "Good Stuff"

I'm ok for cash, so I ordered a new tank anyway, but would be interested in what the latest thinking is in the UK. keep um or bin them?

Matt

[Chris Cherrington]

IIRC there are some that are affected and others not and that the way to tell is the tank number, not the age. I would check that out first before binning it!!

The test should include an ultrasound fracture check and it is possible the ones you had problems with were tested before this was made mandatory.

I'd check it with an IDEST station as they should have all the relevent numbers dates models etc..

Chris

PS scrap ally is quite high priced now so don't bin it take it to the scrappie

[MattDuke]

IIRC there are some that are affected and others not and that the way to tell is the tank number, not the age. I would check that out first before binning it!!

The test should include an ultrasound fracture check and it is possible the ones you had problems with were tested before this was made mandatory.

I'd check it with an IDEST station as they should have all the relevent numbers dates models etc..

Chris

PS scrap ally is quite high priced now so don't bin it take it to the scrappie

Thanks, as said it's not made from the effected alloy. So I'm more wondering if divers keep using them until they fail, or put an age limit on them. (Just for safetys sake)

[Craig]

Matt,

I could be wrong here but I would keep the cylinder until it fails its annual ultrasonic test.

This is because the cracking phemonenon is not really related to age but to the fact that Al does not have a defined fatigue limit, unlike steel, therefore its chances of failing are related to the amount of time it has been charged / discharged. Of course this can be related to age in that the it is more likely to have been used more the older it gets.

Hope this helps.

[Ben Panter]

I have an alu 7l twinset whose first test stamp date was before my birth. They've been fine, crack test and all. When I get back to the UK I plan to get a steel version and either mothball them or possible move them over to side mounts. I'd say that if they pass the test, they're fine - but of course if they fail the test get rid of them.

Ben

[Chris Cherrington]

...I'm more wondering if divers keep using them until they fail, or put an age limit on them. (Just for safetys sake)

Ali 80s are the standard tank in the US. I doubt that all US divers bin their tanks after 10 years....

Chris

[MattDuke]

Ali 80s are the standard tank in the US. I doubt that all US divers bin their tanks after 10 years....

Chris

Actually it was my local supplier of ali80's who was the one talking about binning them after a year! That makes business sense I guess!

[Phil Laughton]

Ali cylinders made pre 1995 to BS 5045-3 A or B must be tested using the Visual Plus method as well as the normal hydraulic test.
Ali cylinders made post 1995 to BS 5045-3 C were made of a different grade of aluminium and only require the periodic hydraulic test.

[MattDuke]

Ali cylinders made pre 1995 to BS 5045-3 A or B must be tested using the Visual Plus method as well as the normal hydraulic test.
Ali cylinders made post 1995 to BS 5045-3 C were made of a different grade of aluminium and only require the periodic hydraulic test.

yep, as said I have the "Good Stuff" (BS 5045-3 C ) and I am aware that there are no rules other than standard hydro test.

Just wondered if anyone put an age limit on their tanks voluntarily. Seems not! :)

[Gordon]

People might not use them any more, but to throw away diving kit :eek: thats a stoning offence

[tony J]

The test should include an ultrasound fracture check

<pedant>

I assume it is actually NDT eddy currents not ultrasound. They are looking for cracks in the metal not how pregnant the cyclinders are.
</pedant>

[Adrian Kelland]

<pedant>

I assume it is actually NDT eddy currents not ultrasound. They are looking for cracks in the metal not how pregnant the cyclinders are.
</pedant>
Aye it is an eddy current test. I have been told that it is possible for cylinder to fail the test if there is a level of oxidisation/corrosion. Don't know how true this is. I have an old cylinder that keep passing the test, so I am happy. For now.

[Chris Cherrington]

<pedant>
They are looking for cracks in the metal not how pregnant the cyclinders are.
</pedant>

[uber pedant]

Ultrasound testing has many uses not just medical and within the medical sphere many uses not just inspections of foetal development.

[/uber pedant]

Chris :rolleyes:

[MattDuke]

This was a response I got from a friend:

Well, Alu, any alloy, scores very low in any fatigue test. Dur-Alu, the type used in aeroplanes, is maybe the most resilient, but even this cracks regularly, and then it' s a
matter of detecting the crack and monitoring its creep... (This is one of my areas I work with, not planes, but in offshore constructions)

The fatigue-issue is a equation where the factors are usage x stress. I.e the number of times you fill a cylinder. Therefor a tank that has been used extensivly, is more likely to fail at some point.
When it comes to surface cracks, they are most likely to occur in the threads of the valve. Therefor inspectors, like XXX, is adviced to pay special focus on the threads when inspecting.
Ofcourse if you use your tank very much, and always has it inspected and pressuretestet, chances are it will be discovered during an inspection, and if XXX detects a crack, he must destroy it.

The downside here is that the only inspection that is done is visual, and that gives a theroretic chance a crack will go undetected. Therefor a safe advice is to scrap it after ten years, Id say.
Alu differs from steel when it comes to fatigue... Crack-Creep-Speed... Not an issue for steel-cylinders... an issue for alu... The thing is that the creep will be initiated during stress, i.e. when you
pressure-test it... if it afterwards are left in your garage filled with gas-pressure, a crack will creep... and in time explode. This is a fact. Therefor a alu-bottle should not be left in storage with gaspressure
over time.

My opinion, I scrap mine after ten years... safe

[Speedhound]

Hi,

One of my stage tanks is now 10 years old, last hydro/clean was 12 months ago.

I was advised by a few friends that once the cylinder reaches 10 years old, I would be best destroying it, as aluminium can quickly form dangerous cracking, even if it has recently been tested.

Our club has had two catastrophic failures of tanks over the last 15 years. Both aluminium, both "in test", both old cylinders. One failed during filling, and it destroyed a portion of the compressor room roof. One failed hours after filling, in a members garage, destroying part of the wall and significantly damaging his car.

I have been aware of a few things on Alu tanks, since I started diving in 1992.

My tank is a luxfor, but the alloy type is not effected by these documented stress fractures:

http://www.divernet.com/news/items/luxfer050500.htm

http://lists.drogon.net/scuba-uk-ndg/archive/scuba-uk/2000/q1/msg01333.html


So therefore, we are just back to having a standard alu cylinder that is 10 years old, and made from the "Good Stuff"

I'm ok for cash, so I ordered a new tank anyway, but would be interested in what the latest thinking is in the UK. keep um or bin them?

Matt


In the US, Al80s are the standard tanks for most rec divers. There was an issue with tanks using a particular Aluminium alloy (6351) back in the '80s and '90s. Any tank made from this alloy and still in use should be destroyed/recycled. Tanks not made from this alloy are fine to use beyond 10 years - as long as they pass the appropriate tests.

The standard procedure here is that we have a visual inspection on our tanks annually, and a hydrostatic test every five years - re-stamped if they pass. Some places also carry out eddy-current testing but I don't know how often. There are tanks that my LDS has, and uses, that have two or three stamps on them, besides the original - so would have to be over 15-20 years old. As long as they pass test they can be used.

[aparsons]

I have an aluminium cylinder that I want to bring into test and into use. It was made in US by Catalina Cylinders, Hampton, Virginia and seems in very good condition. It has the following marking on the top:
DOT-3AL 3000 AC88517 CLIFFDIV 8 C 95 S-80 TC-3ALM207

This indicates that it is a 207 bar cylinder which will be just fine for me.

Under the new regulations does it need a NDT eddy current test and if it passes test can it be filled and used here. I ask that because I had some peculiar conversations with people who say it is "illegal". These seems odd to me as it is properly made to the US and Canadian regulations and these cylinders are used the world over.

There is surely no reason once it has been properly tested why it cannot filled and used like any other cylinder.

From my understanding it needs a hydraulic test every five years and a visual test every two and a half. What is the deal with IDEST? Is it an official organisation or what? I live near Swanage so any recommendations of where I could get it tested would be welcome.

Thoughts and expertise on the current regulations regarding Aluminium cylinders would be most welcome.
Thanks,
Andrew Parsons

[Nigel Hewitt]

I have an aluminium cylinder that I want to bring into test and into use. It was made in US by Catalina Cylinders, Hampton, Virginia and seems in very good condition. It has the following marking on the top:
DOT-3AL 3000 AC88517 CLIFFDIV 8 C 95 S-80 TC-3ALM207
It's USA not UK spec so most shops won't touch it and most test houses the same.
Sorry.
That's just how thing are.