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Post by diverdon on Jul 18, 2014 10:00:25 GMT -8
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Post by nikeajax on Jul 18, 2014 10:40:52 GMT -8
Don, those aluminum tank are probably STILL GOOD! Do what you want with them, but just because they're the older type doesn't mean they are bad: do you know for sure they have been filled passed their marked capacity? An eddy-current-test will determine weather or not they are faulty... The reason why these kinds of tank have a very bad rep is that people were filling them beyond their stated capacity: this is the equivalent of taking the family car to the drag-strip and trying to keep up with something like this: It's going to fail very quickly... Jaybird
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Post by luis on Jul 18, 2014 11:12:06 GMT -8
Jaybird,
That is not true. Sustain load cracking has been found on many tanks that have never been over filled.
There has not been any catastrophic failure in a while because of the inspection procedures. But the rate of failure due to the large number of cracks found in AL6351 tanks is alarming.
I have personally seen too many of the old aluminum tanks with cracks and I don't even work at a dive shop anymore.
When I hang around at my LDS, I often help out by filling tanks, but I will not fill any AL6351 cylinder anymore. It is just not worth it. The failure rate is just too high.
They are being condemned at inspection, but it only takes one careless inspector and the consequences are not worth the risk.
Saying that only over filled tanks are failing is just not true. It is due to sustained load, not over-filled load.
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Post by diverdon on Jul 18, 2014 11:12:10 GMT -8
Yeah, he's got me on the straight stretches. But my Ford Focus corners on a dime I guess I could drop $20 or so on each of the tanks and I might on the 50s, if they'll test them and do a visual eddy. Meantime they'll stay in the garage until I decide what to do about them. I'm really diggen the vintage stuff right now and want to put some smaller doubles together. I think the steel 40's (if that what they are) would make a sweet set of doubles, and the aluminum 50's??? maybe good checking regs and such... Thanks, Don
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Post by diverdon on Jul 18, 2014 11:18:34 GMT -8
When I hang around at my LDS, I often help out by filling tanks, but I will not fill any AL6351 cylinder anymore. It is just not worth it. The failure rate is just too high. They are being condemned at inspection, but it only takes one careless inspector and the consequences are not worth the risk. Thats why I was planning on cutting them up. Considering the mixed messages I've been getting from the shop I deal with (90 miles away) I'm not sure I want to take a chance with them. I have plenty of tanks. Why chance these? Luis, These look like 40's to you? I've never worked at a dive shop, so I'm not familiar with all the sizes they had in 1970. Heck I was 4 at the time;) Don
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Post by luis on Jul 18, 2014 12:26:03 GMT -8
Considering the pressure, I think they are 45's. I think they are a bit short to be 50's, but the only way to really know is to measure the inside volume.
It is very easy to accurately measure the inside volume during the hydro. Just measure the weight of the empty tank (with the boot but no valve) and then measure the weight of the tank full of water. The difference is the weight of the water. Using the density of water you can get a very precise internal volume (density about 62.3 lb/ft^3 or 0.036 lb/in^3, @ room temperature).
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Post by rhwestfall on Jul 18, 2014 12:27:45 GMT -8
they are so short, they will likely make you real "front heavy" when twinned........
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Post by SeaRat on Jul 18, 2014 13:19:56 GMT -8
they are so short, they will likely make you real "front heavy" when twinned........ Actually, the twin shorter tanks (42s, 45s, 50s) are very nice with a double hose regulator. It is easier to get the regulator lower for optimal positioning on the back, and you can easily sit down on a rock or boat bench (or pool bench) when donning things. They don't make you front heavy at all, probably because they are usually either slightly negative, or even positive (my twin steel 52s), in buoyancy underwater. I currently own two single AL 80s, and a set of twin AL 50s. I have not yet drilled my AL tanks, but they are sitting without air as desplay units and I don't currently have plans to re-hydro them (they have gone out of hydro). As Luis has stated, I feel that the sustained load cracking is a huge issue that one must keep on top of if these tanks remain in service. My LDS will fill them (if they are current on hydro/eddy testing/visual inspection), but really don't want them to. I got the twin 52s (steel) as replacement for the twin AL 50s. I do have a set of three UDS AL tanks, and am trying to get them back into condition to dive. But that means that PSI/PCI will have to come up with an Eddy Current Tester for them. If they do, then I probably will get this unique set back up and running. But currently, they are broken down and without pressure. It's hard to get a sustained load cracking situation without the load (pressure). John
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Post by rhwestfall on Jul 18, 2014 15:31:48 GMT -8
True specifically in a DH configuration, if worn properly. FWIW, I dive a AL63 twinset. But steel HP80's and a MP72 as a single tip me horribly forward in a single tank or on a modern backplate...
Just some food for thought to be aware of...
It also becomes a challenge to obtain the low enough placement to keep the balance good and still have adequate hose length in currently "standard" hose lengths.
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Post by SeaRat on Jul 18, 2014 16:48:34 GMT -8
I switched away from the "standard" hose length years ago, when I bought longer hoses for my Aquamaster, and later bought SCBA hoses for my USD Overpressure Breathing single stage regulator (predecessor to the USD Mistral). I now use Super-Flex hoses and a Hope-Page mouthpiece on my Mossback Mark 3 regulator. I still have some with standard length hoses, and find them okay underwater, but on the surface they are a bit short. Here are some photos with me using my twin 45s (Sherwood, 1800 psig steel) with the USD Overpressure Breathing regulator and long hoses at High Rocks on the Clackamas River several year ago. John
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Post by scubadiverbob on Jul 18, 2014 16:50:38 GMT -8
I got a 13 cu.ft. experimental aluminum tank and I keep 200 psi in it to fill bike tires (I have an old first stage rigged up for that). Do you all think 200 psi in a tank would make it blow up from sustained cracking?
Also, I think (I might be wrong and this may have changed) that if the hydro shop does the visual and eddy current testing, and stamps the tank that they did the eddy current test when they did the hydro, that the tank is legal to fill. They have a stamp that goes where the "+" goes for tanks that are rated for an overfill. Would have to check DOT regulations. Also, I've been told that if you don't transport the tanks on the highway, DOT regulations don't apply ... probably wrong on that one.
Robert
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Post by scubadiverbob on Jul 18, 2014 16:52:15 GMT -8
.... and I've also been told "It's better to be safe; than, sorry"
So, will 200 psi in a tank cause it to explode?
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Post by SeaRat on Jul 18, 2014 17:07:21 GMT -8
.... and I've also been told "It's better to be safe; than, sorry" So, will 200 psi in a tank cause it to explode? I doubt it...but 3000 psig over a longer period of time causes these problems with sustained load cracking. Here is one of the best explanations I know of for sustained load cracking by PSI-PCI, Inc.'s Bill High: Cracking and Ruptures of SCBA and SCUBA Aluminum Cylinders (Made From 6352 Alloy)John
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Post by nikeajax on Jul 18, 2014 17:22:16 GMT -8
Again, John--THANK YOU!
"In 1985, PSI, Inc. (now PSI-PCI, Inc.) became the first dive industry advocate to focus on SLC detection using a mirror and light inspection protocol. Although cylinder visual inspectors were warned to examine crown and threads of SCUBA 3000 psig and SCBA 2216 psig cylinders, few technicians heeded the warning. Tests conducted by Luxfer USA suggested that cylinders with service pressure of 3000 psig or less were unlikely to rupture even if SLC developed. Inspectors trained by PSI-PCI, Inc. did find a number of cracked cylinders as well as some cylinders leaking from outer-crown cracks, before the first SCUBA cylinder ruptured in Australia in 1988. Subsequently, DOT, Luxfer USA and PSI-PCI, Inc. stepped up efforts to educate both owners and inspectors of 6351 alloy cylinders about the importance of thorough technical inspections.
Evidence indicated that SLC develops slowly over a multi-year period. For example, detailed metallurgical examination of one ruptured SCUBA cylinder showed that the crack had been growing for eight years or more and would have been visible for about six years to a trained inspector using the proper crack-assessment protocol. Had that cylinder been carefully inspected, it could have been removed from service long before the rupture occurred."
Jaybird
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Post by rhwestfall on Jul 19, 2014 8:56:42 GMT -8
I switched away from the "standard" hose length years ago, when I bought longer hoses for my Aquamaster, and later bought SCBA hoses for my USD Overpressure Breathing single stage regulator (predecessor to the USD Mistral). I now use Super-Flex hoses and a Hope-Page mouthpiece on my Mossback Mark 3 regulator. I still have some with standard length hoses, and find them okay underwater, but on the surface they are a bit short. Here are some photos with me using my twin 45s (Sherwood, 1800 psig steel) with the USD Overpressure Breathing regulator and long hoses at High Rocks on the Clackamas River several year ago. John source?
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