The tank that went BOOM!

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Cool link.
Are you supposed to fill tanks in 3 minutes?
 
I warned 'em about that nitrous oxide-acetylene-propane party mix! Did they listen???
But seriously folks, all HP bottles are potentially dangerous, VIPs and hydros notwithstanding. Well-maintained bottles will last almost indefinately. Industrial HP flasks are still commonly encountered -- and in service -- with head stamps from WW I. Yes, you heard right, World War ONE. Needless to say, these are all steel.
I suspect that maybe this aluminum bottle was subjected to some prior overfilling and/or other abuse. Then again, according to the story, the operator left the tank unattended while being filled. I don't think this is ever a good idea.

Best regards
Doc
 
he should have been standing right there, ok.
I am not trying to start a fight or anything, that just sounds a little off to me, not that I know anything about filling tanks.
 
No, I'm not suggesting that he should have stood over the tank or been holding it in his arms, but he seems to have gone off to deal with a customer and left the filling to his regulator setting. This is not an uncommon practice, but maybe he was harried and the reg wasn't set correctly, maybe something distracted him, maybe the reg failed, or maybe none of the above pertained, but the point is that he apparently wasn't personally monitoring the fill. He estimated a failure pressure, but couldn't say, "I was watching the gauge and it blew at such-and-such psi."
I don't know why it blew and neither does the guy who did the fill. I think it's good practice to watch the pressure gauges when filling an HP bottle.

Best regards
Doc
 
I agree that it would make sense to monitor the tank while it is filling, and I can see how that could have prevented a problem, I just thought it funny to think that he should have been there when it blew, like he could have done anything about it, assuming that it did blow at 2200 like he thinks.
But, hey, what do I know.
 
The real reason this tank failed is that it was made by Luxfer before about 1990. There have been several failures of these tanks here in New Zealand so I presume it must be reasonably common elsewhere. When one of our LDS owners had a leg removed by one 3 years ago there was a ban on filling them for several weeks. My sister dived with the guy concerned and assured me he very safety conscious. The investigation put the cause down to sustained load cracking.
Here's a link that talks about this incident and the problem with some aluminium tanks.

http://www.divenewzealand.com/53tank1.html
 
1) The cylinder did not fail because Luxfer made it before 1990.

2) Cylinder failures like this are not common ANYWHERE.

The cylinder failed because the “self-regulating” SCUBA industry isn’t doing a very good job of self-regulating and better wake up before that option is taken away. Sustained load cracking, or SLC does happen with 6351 alloy, this is a given. Luxfer was one of several manufacturers that made AL cylinders out of 6351. There’s a long history of different AL alloys. 6351 is just one of them. WE THINK they have a shorter lifetime than the current 6061 alloy, but 6061 hasn’t been used nearly as long as the 6351 alloy.

In other words, it appears that the 6351 has a finite lifetime and we just don’t know about 6061 yet (but lab results seem to point to the conclusion that it’s a better alloy).

So, are 6351 cylinders dangerous? No. Not by ANY common measure of safety. After on the order of hundreds of millions of fillings we have somewhere between 20 and 30 cylinders failing from SLC. Hence this is not a common failure ANYWHERE.

If SLC failures happened without any warning even this tiny, statistically insignificant amount could perhaps be considered dangerous. However, SLC typically develops over three to five years, which means you don’t just get one or two shots at detecting it during a visual inspection, you get a minimum of three chances to discover SLC and take the cylinder out of service.

This is where the dive shops are failing, and where many are making matters worse. Many dive shops do not have qualified inspectors on staff, and/or consider an inspection a cursory glance in a cylinder to see if there’s any corrosion. Inspecting the threads takes time and effort, and many shops don’t expend that time and effort and THAT’S why we have cylinders letting go. You don’t need an eddy tester to see if they’re cracks in threads, it just speeds up the inspection process. A good visual inspection will discover cracks. Every time an AL cylinder lets go due to SLC, you know that there are at least three bad inspectors behind the explosion. THAT’S the problem, not 6351. Everything wears out, with something catastrophic like a cylinder letting go, you better have a good way of finding out when it’s wearing out. An inspection, if correctly done, does just that.

Where shops are making matters worse is that some shops are starting to refuse to fill 6351 cylinders citing their concern over the alloy. Who knows if this is a genuine concern over the minimum-wage shop monkey that fills cylinders, or the far more likely reason that they can sell a newer cylinder (ka-ching! $) to the typical uninformed diver that believes everything that shop tells ‘em. The result is the same, the shop is admitting that the visual inspection protocol that their self-regulated industry has set up isn’t being implemented correctly. Hello big-government regulation if the industry doesn’t clean house and soon. Some shops are doing the right thing and offering free eddy current testing of cylinders (http://fdu.com/tanksafetyalert.htm for example). While this still admits that the current process is broken, they’re at least doing their part to fix it AND they’re not shafting the customer for the industry’s failings.

The neck picture in http://www.airsource-one.com/bea8.jpg shows what is currently thought to be the fingerprint of an SLC fracture. See the “shadows” on both sides, the right side about half way between the threads and the edge of the picture, the left side almost to the edge of the picture? Current theory is that this is oxidation on the faces of the crack, so these were HUGE cracks before the cylinder went, both extending at least an inch away from the threads.

If you want some good, sane reading on SLC, rather than FUD, turn to Bill High, the president of Professional SCUBA inspectors, inc.: http://www.psicylinders.com/message.html.

As for the article http://www.divenewzealand.com/53tank1.html, the fact that he’s wet filling is a show of ignorance right then and there, so the article’s author immediately becomes suspect.

But to assume that this author really is seeing SLC failures left and right whereas the US as a whole has only seen a little more than 10 brings me to an interesting theory. The US requires a hydro only once every five years where NZ requires them every other year. Could the more frequent testing be the problem down there? It wouldn’t be the first time that a government-dictated “cure” was worse than the disease itself.

Roak
 
ok, I admit it I don't trust other inspectors. We fill these tanks but they scare the hell out of me. When I dive I also trust very few. When I drive I trust very few. Seems to work. I don't want my life depending on the skill of someone in another shop. I have seen them dive. If they inspect like they dive I am a dead man for sure. I don't care if I never sell another tank not enough mark up to make it worth the time it takes to write the receipt, inspect, fill ect. No min wage monkeys to fill in my shop. The only monkeys are me and my wife, the owners. I hope that someday we can get rid of these tanks. For what a new al tank costs if you can't afford it you don't need to be diving. Save your penneys and come back when you can play right. I do not want to die standing there filling a tank (no money in fills either).

You should see some of the ancient tanks we get in. Hey after twenty of thirty years you got your moneys worth. Don't be a cheap sob. Buy a new tank. Buy it from someone else, but let me live through the fill.

Then there are the cheap BASTAR*S that buy some old junk tank at a yard sale. They get a great deal but I have to deal with the piece of junk.
 
https://www.shearwater.com/products/peregrine/

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