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Post by snark3 on Jul 11, 2019 10:11:43 GMT -8
In the link I provided the pictures show the explosive power, and what can happen. The tank pictured exploded between 1500 and 2000 psi while being refilled. Fortunately in the incident mentioned nobody was seriously injured.
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Post by SeaRat on Jul 11, 2019 10:39:18 GMT -8
In the link I provided the pictures show the explosive power, and what can happen. The tank pictured exploded between 1500 and 2000 psi while being refilled. Fortunately in the incident mentioned nobody was seriously injured. For those who won't go to the link, here's the photos Snark3 mentioned above: From the article: This is why I have two aluminum 80s and double AL 50s sitting without air, decommissioned. They have been replaced by a new AL45 twin set, my steel 72s and a twin steel 52 set from USD. John
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Post by snark3 on Jul 11, 2019 13:39:04 GMT -8
John- Thank you for putting this information where everyone can see it. We all like to dive vintage equipment, and these old aluminum tanks certainly are vintage. I believe however that because we're diving vintage equipment, which many will say is unsafe, we need to make sure we do it safer than the modern divers. I personally don't believe these old aluminum tanks are worth taking a chance on, particularly when you can pick up steel 72's for next to nothing.
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Post by technidiver on Jul 11, 2019 14:01:07 GMT -8
I agree with Skip here. One bad story about a vintage diver ruins the whole vintage community.
The 72 has the best track record. Be safe, buy local, go get a 72.
TD
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Post by luis on Jul 11, 2019 18:57:27 GMT -8
We have had many heated debates about the subject of the older aluminum tanks: but the reason why these tanks need to be hydro'ed is because they can and will crack under sustained loads. The critical test is the eddy current testing: this is used to find any cracking that might be happening, and it begins at a microscopic level and can take years to where they will have catastrophic-failures. The industry switched the alloy because of this type of sustained load cracking: as of now, the newer tanks do not crack like the older ones can. I own one of these tanks, and if I use it, I make very certain that the eddy testing is up to date. I may be wrong, but, I believe it was Luis who said they fail when they are being refilled, not while in a diving situation. But, what I do remember is, him saying is that a friend of his was killed when one of these tanks exploded: with very good reason this subject is something that gets his hackles-up! JB I can attest to that. A few years ago I took my beloved yellow USD Twin 50's in for hydro and eddy testing because they were the BAD alloy. Both passed. I was ecstatic as I bought them new in 1976 and we had shared many an adventure together. Alas, on first fill post hydro/eddy testing I was getting micro bubbles out around one neck-valve seal. Changed o-rings again, even took a dremmel and some polishing brushes to clean out the seal area. Took a while of eliminating leak possibilities. Finally got out my son's old microscope and took a peak at the threads. Sure enough you bet your sweet bippy there was the itty bitty hairline crack running up through the neck threads. My beloved tanks are now a giant paperweight. M This is the 3rd case that I have heard (from what I consider a reliable source) of an Al 6351 cylinder that passed hydro test, VIP, and eddy current testing; no cracks were detected during the re-qualification inspections and testing, but then a crack was detected on the neck due to air leaking during the air filling process. That has to be one of the scariest situations to be in. Almost as been suddenly promoted to a field EOD (Explosive Ordinance Division) position. I am certified to inspect these cylinders (including eddy current testing), but I don’t want anything to do with these cylinders (Al 6351). It is just not worth it. I have newer Al 6061 cylinders and steel (St 72, etc) some dating back to the mid 50’s. We haven’t had very many catastrophic failures of the Al6351 since the more stringent inspections have been introduced, but IMHO there are two major reasons why we haven’t seen more failures. 1) The inspection does remove many cylinders out of service before they become an issue. Just from personal observations and talking to dive shops there are a high number of cylinders that are removed from service with detectable cracks. 2) AL 6351 are getting removed out of service in large quantities even before a crack is detected: 2a) Probably many more of these older cylinders have been removed from service because in many parts of the country (including Florida, and LDS in many other states) just don’t want to take the risk and deal with them. 2b) Also in the Caribbean were many dive operators with large numbers of aluminum cylinders, but limited or no access to hydro testing facilities, many cylinders are constantly removed from service. It is not uncommon for many cylinders to be just removed from service after 10 or 20 years of service. I am referring about large rental fleets were the cylinders get a lot of use and abuse.
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