Dive Cylinder Explodes - Sydney

[DMarelli]

This is another unfortunate incident that resulted from the breakdown of the inspection protocol. I don't know the Australian law but in the US annual internal inspection is voluntary, DOT requires inspection only at the 5-year hydro test interval. Their metallurgists estimate that a crack in the neck area (where they always fail first) will take may years to become an explosion so so a proper formal inspection should catch such cylinders. DOT still allows the 6351 alloy to remain in service as long as the cylinders pass visual and hydrostatic testing. This is actually a reasonable approach. Cylinders are not required to be filled in a blast containment cage, though this would be a very good idea. I am not sure whether this was even a 6351 cylinder, but that is a red herring since it had been out of hydro test for 14 years. It is difficult in some places (like Florida) to get older aluminum cylinders filled because the dive shop owners and employees are afraid of them as a result of their lack of knowledge and their poor inspection practices. I heard one shop employee in Glens Falls NY tell a customer that it was illegal to fill his 6351 T6 cylinder (untrue). If shops and individuals are not doing proper formal inspections at least annually and using eddy current technology on EVERY aluminum cylinder than they are not doing a proper job.

 

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). If shops and individuals are not doing proper formal inspections at least annually and using eddy current technology on EVERY aluminum cylinder than they are not doing a proper job.

The two best reasons for shops to require Eddy test on 6061 aluminum cylinders is to keep the sky from falling and to pay for the test device the shop purchased.

Neck cracks are no more a problem with 6061 tanks than they are with steel tanks. The shop that wants to charge me extra for an Eddy test on my 6061 cylinders loses my business.

 

[DMarelli]

The two best reasons for shops to require Eddy test on 6061 aluminum cylinders is to keep the sky from falling and to pay for the test device the shop purchased.

Neck cracks are no more a problem with 6061 tanks than they are with steel tanks. The shop that wants to charge me extra for an Eddy test on my 6061 cylinders loses my business.

The statement that 6061 T6 cylinder do not crack is is not true, much like most "general knowledge" about compressed-gas cylinders. Luxfer has had 6061 T6 cylinders that developed cracks at their first hydrostatic test interval, only 5 years old! and were replaced by them (and they acknowledged that the cylinders did indeed crack). The current failure is based on one thread cracking, whereas it used to be 3. I personally failed 2 of these cylinders and my local dive shop had 9 fail as a result of thread cracks. The part about steel cylinders not cracking is accurate. Steel cylinders that are properly cared for are the safest ones to use. So I never inspect an aluminum cylinder without using the eddy current device, it adds to the safety of the dive shop employees and the general public.

 

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The statement that 6061 T6 cylinder do not crack is is not true, much like most "general knowledge" about compressed-gas cylinders. Luxfer has had 6061 T6 cylinders that developed cracks at their first hydrostatic test interval, only 5 years old! and were replaced by them (and they acknowledged that the cylinders did indeed crack). The current failure is based on one thread cracking, whereas it used to be 3. I personally failed 2 of these cylinders and my local dive shop had 9 fail as a result of thread cracks. The part about steel cylinders not cracking is accurate. Steel cylinders that are properly cared for are the safest ones to use. So I never inspect an aluminum cylinder without using the eddy current device, it adds to the safety of the dive shop employees and the general public.

Can you link to reports?

I find this:. Luxfer updates inspection and replacement policy for scuba cylinders manufactured in the United States

Where Luxfer verifies that SLC does not occur in their 6061 tanks and limits the use of VE devices due to false positive results. They do reiterate the need for trained inspectors to visually inspect all tanks for recognized potential defects.

 

[DMarelli]

I don't have Luxfer internal reports, I only know that I have first-hand experience with cracks in 6061 T6 cylinders. They replaced all of the cylinders that had cracks no question. I was never sent a piece of paper that said the cylinders were cracked but I did receive an oral confirmation on the 2 that I sent to the testing facility that they were indeed cracked. The early eddy current machines (Visual Plus and Visual Eddy) did have issues with false positives for 6061 T6 but both manufacturers solved those problems and the machines work with either alloy if you properly set them up. In fact it is essential that SCBAs undergo eddy current detection since the aluminum liner in them is so thin. Current SCBAs also use 6061 T6 (no surprise). I own a Visual Eddy machine and my local dive shop uses the Visual Plus machine. We consult with each other on difficult "diagnoses" and both machines have detected cracks in 6061 T6 cylinders. As far as the number of cylinders we have seen here in north Florida that were cracked I suspect that there was an issue with a particular batch of cylinders. The 6061 alloy is much more resistent to SLC, as you know, but I would never say that it is immune to SLC. Then again I am a biologist and not a metallurgist, my goal is to keep people safe. I don't work at a dive shop but I do inspections.

 

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I don't have Luxfer internal reports, I only know that I have first-hand experience with cracks in 6061 T6 cylinders. They replaced all of the cylinders that had cracks no question. I was never sent a piece of paper that said the cylinders were cracked but I did receive an oral confirmation on the 2 that I sent to the testing facility that they were indeed cracked. The early eddy current machines (Visual Plus and Visual Eddy) did have issues with false positives for 6061 T6 but both manufacturers solved those problems and the machines work with either alloy if you properly set them up. In fact it is essential that SCBAs undergo eddy current detection since the aluminum liner in them is so thin. Current SCBAs also use 6061 T6 (no surprise). I own a Visual Eddy machine and my local dive shop uses the Visual Plus machine. We consult with each other on difficult "diagnoses" and both machines have detected cracks in 6061 T6 cylinders. As far as the number of cylinders we have seen here in north Florida that were cracked I suspect that there was an issue with a particular batch of cylinders. The 6061 alloy is much more resistent to SLC, as you know, but I would never say that it is immune to SLC. Then again I am a biologist and not a metallurgist, my goal is to keep people safe. I don't work at a dive shop but I do inspections.

From Luxfer:. If Luxfer 6061-alloy cylinders are not susceptible to SLC, why has Luxfer exchanged 6061 cylinders that have been reported to have cracks?

Could your tanks been among those returned that were all found to be OK?

 

[DMarelli]

I am guessing that this is a CYA press release. The eddy current test is a tool, it can detect small voids but eyes can also see the cracks, which was the case in all of the cylinders I am mentioning. We saw with the other tools we have that the thread was cracked, the eddy current detector simply confirmed it. 1200 is a lot of false positives considering that the eddy current machines corrected that problem maybe 13 years ago. If a cylinder was not found to be cracked and deemed OK why did they replace them? And they did verbally confirm that they were cracked. I don't see this as a huge problem, good inspection will find bad cylinders but I also don't believe that aluminum is the best material for cylinders.

 

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While I can accept the idea that a manufacturing defect may result in neck cracks in any scuba tank, it seems quite clear that SLC is a phenomena associated ONLY with 6351.

I will not pay a shop extra for them to do a VE on my 6061 or steel tanks.

 

[DA Aquamaster]

I'm in agreement with AWAP on this issue.

Luxfer can't afford the liability of telling someone their tank isn't cracked when an over eager or over zealous inspector decides gets a false positive, or decides a fold is a crack, so of course they'll replace it no questions asked.

The reality is that no properly inspected 6351-T6 alloy tank has catastrophically failed due to SLC since eddy current protocols were put in place.

The DOT determined after years of tests and field experience with the luxfer initiated 18 month eddy current protocol that adding a visual eddy inspection to the standard requalification protocol is more than sufficient to prevent a crack from propagating from first detection to catastrophic failure. And that is with most RINs doing the visual and VE portions of the requalification prior to the hydro test portion of the requalification.

If a shop back stops that 5 year VE with an annual VE or visual plus inspection as part of the shops scuba industry VIP, then it's just and added layer of safety. Given the order of VE and hydro tests by RINs and the potential for a non detectable crack to be come detectable after the hydro test, I'm ok with a shop doing a VE or Visual Plus as part of an annual VIP for a 6351-T6 alloy tank, but only if the charge is reasonable.

Doing it on a 6061-T6 alloy tank is a waste of the customers money. If the shop wants to do it for their own piece of mind, they can go right ahead, but they should not be expecting the customer to pay for it.