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Post by surflung on Oct 2, 2015 10:54:08 GMT -8
Failed Visual on 1970's Aluminum Tanks - Just got off the phone with MN School of Diving: One of my aluminum 50 cu ft tanks from the 1970s failed the visual inspection recently and I thought I'd post the story here in case its of value to anyone. - I got my Twin 50s as payment from my Dad for painting the house back in 1973 or so. They didn't actually get used very much after the first year or so. They were stored in like new condition ever since then. So when I took up vintage diving 4-5 years ago I was surprised at some people telling me my essentially new tanks should be retired due to the Sustained Load Cracking risk. - The local dive shop assured me that if they passed visual every year they should be fine. And in fact, I looked inside the tanks myself and they were shiney and new... How could there be anything wrong? - This Summer I brought them in for a visual along with some other tanks and all of the tanks passed visual inspection. However some of the tanks came back with the wrong O-Ring between the valve and tank and I had to replace them. This got me wondering about the reliability of the visual inspection on the two 50s. - Then Tom (Retpo) said he took the inspection course a few years back where he learned the SLC cracks could appear at anytime and promptly retired his older aluminum tanks. And then even more discussion on this forum from a couple of members who recommended storing the older aluminum tanks with low pressure until you need to use them. I saw another website where they said as long as you inspect them yearly, they're fine. And yet another on-line friend said the only reason we haven't seen more tanks blown up from SLC is because the inspection programs have been catching it and pulling the bad tanks out of service. - Lots of smart people and good advice but I have sentimental value in these tanks and just wanted to be sure before I take them out of service. So, I resolved to take the tanks up to MN School of Diving where they have the Eddy Current Visual inspection and also to ask the advice of Bill Matthies. Bill has let me watch my hydro tests in the past and really seems to know what he's doing from having years of experience. - He wasn't there when I dropped off the tanks but I called him today and darned if one of the tanks failed the Eddy Current Visual. And here's where it gets interesting. He says the Eddy Current test is his "Visual". Where the earlier dive shop passed this tank after inspecting with eyeballs and a magnifying glass, the Eddy Current process is fool proof whether you can see a crack with the naked eye or not. And, it gets the same result regardless of how many times you do it or who is doing it. (This is my understanding of Bill's explanation.) - Surprisingly the other tank passed the Eddy Visual just fine. And Bill said he has no problem with filling the older aluminum tanks as long as they pass the regular Eddy Visual inspection every year.
So the one tank has to be condemned. The other one I'll go ahead and hydrotest for now. But the writing is on the wall and I'm probably never going to fill it again. Moral of the story is this: An eyeball visual inspection is no guarantee that these older aluminum tanks haven't got a problem. The Eddy Current Visual will tell it like it is.
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Post by nikeajax on Oct 2, 2015 14:25:28 GMT -8
Eb, contrary to popular myth, they don't just blow up with spectacular failure... These cracks start VERY small, and VERY slowly... "Sustained Load Cracking, a metallurgical anomaly, occasionally develops in high- pressure cylinders made from 6351 aluminum alloy. As the name implies, SLC usually occurs in cylinders that have remained filled for sustained periods of time. U.S. manufacturers began using 6351 when aluminum alloy cylinders were approved by the DOT for U.S. service under various special permits beginning in 1971. Manufacturers included Luxfer USA, Walter Kidde, Norris Industries and Kaiser Aluminum. Permits for Norris and Kaiser (SP6688 and SP6576) have expired and those cylinders are no longer approved for use in the U.S. but may be used in Canada under a grandfather clause. Walter Kidde continued using 6351-alloy until the end of its cylinder production in 1989.
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."Quoted from: www.hawaii.edu/ehso/diving/Cracking%20and%20Ruptures%20of%20SCBA%20and%20SCUBA%20Aluminum%20Cylinders.pdf This is your decision to make, but again, they don't just blow up arbitrarily! If this tank was mine, I'd use it until it was deemed unsafe, but use until then. Yeah, I know I'm just a commie pinko punk that thinks he knows everything But, because it has such sentimental value to you, this should be even more reason to use it until you can't, because in a sense, your father is with you when you're using it for what they were meant to be used for! With good care, it might even outlast you, for your kids to use... JB
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Post by luis on Oct 2, 2015 15:22:11 GMT -8
You are quoting from an old document from Bill High. A lot has changed since that was written. Personally, I have seen too many cylinder developing neck cracks due to SLC. The rate at which they are being pulled out of service due to confirmed cracks is IMO, alarming. A personal acquaintance of mine lost his life in Mexico last year while filling an older aluminum cylinder. The tank ruptured and ripped his leg at thigh level and he bled to death out of his femoral artery in a few minutes. The cylinder ruptured due to confirmed SLC. You may notice the last quote talks about: You do not see that kind of special safeguards recommended when filling any other kind of cylinder. If you feel like taking unnecessary risk… It is totally your choice Below is some quotes from the DOT CFR. I work and read a lot of government specs. When I see the term “known safety problem”, I pay special attention. phmsa.dot.gov/pv_obj_cache/pv_obj_id_070BAC50793570923E878B0A7407F70871FA0100/filename/3al_advisory.pdfwww.gpo.gov/fdsys/pkg/FR-2006-08-29/pdf/E6-14255.pdf
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Post by SeaRat on Oct 2, 2015 16:04:02 GMT -8
Eb and Jaybird,
I agree with Luis on this one. As a Certified Safety Professional, I am especially concerned about these tanks. I have personally taken six of these tanks out of service. Two are my twin 50s, which I now use for display purposes only. One is a AL 80 (black, from USD), and three are also from USD, my UDS-1 tanks. The problem with my UDS-1 tanks is that there is no eddy current tester for this size opening. I would really like to get them back in service, but not without this test procedure. I cannot get them hydroed until I can get them eddy current tested, and a custom tester would be very expensive.
I have one AL 80 left, which I use with my Nautilus CVS, as this BCD is made for this tank. I can use a single 72 with the Nautilus CVS, but then the Water Inlet Valve drags on the surface when it is vertical. I will not leave this tank full for very long, and intend to keep that time period less than two weeks. The UDS-1 tanks are at zero pressure, as are the other tanks, so sustained load cracking cannot occur with them.
I replaced my twin AL 50s with twin steel 52s (@1800 psig). I have another set of twin steel 45s, which are my go-to tanks for much of my vintage diving (see "Salmon in Trouble" to see those tanks in action).
John
John C. Ratliff, CSP, CIH, MSPH
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Post by duckbill on Oct 2, 2015 16:47:04 GMT -8
So, I'm sure most of us are wondering the obvious.....how much pressure was in the cylinders during their 35 years in storage?
Sad to lose something sentimental, but you still have them for display. Maybe consider this an opportunity to "upgrade" to some modern cylinders to go with your new, modern regulator. In color-matched red perhaps?
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Post by nikeajax on Oct 2, 2015 16:57:18 GMT -8
To use Luis' own nomenclature: "SUMMARY: This final rule revises the Hazardous Materials Regulations to address a known safety problem with cylinders manufactured of aluminum alloy 6351–T6. The revisions include an inspection and testing program for early detection of sustained load cracking on cylinders manufactured of aluminum alloy 6351–T6 and used in selfcontained underwater breathing apparatus , self-contained breathing apparatus (SCBA), and oxygen services."What I was saying was, if the tank passes the eddy test, it should be safe to use. What I said was: "If this tank was mine, I'd use it until it was deemed unsafe, but use until then."Eb had stated that one of two of his tanks was deemed unsafe, leaving the one I was referring to, which was deemed safe to use... Jaybird
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Post by SeaRat on Oct 2, 2015 18:17:22 GMT -8
I was wondering about that, Jaybird. Thanks for the clarification. Yes, the tank that passed the eddy current test should be fine to dive, just as the one single AL 80 I'm using for the Nautilus CVS is also fine to dive. My LDS has a whole raft of AL 80 tanks that they still use, and they still fill the Fire Department SCBA tanks made of this aluminum too.
However, just to be clear, it is soooooo tempting to put my other tanks back into service. The one AL 80 tank is the only one I'm leaving in service, and the other is a backup in case sometime down the line this one fails the test. I have over 15 years of diving on the AL 50s, and great memories from them too. They are just the right size to sit down on the rocks, and have the buoyancy characteristics I like. But I'm going to keep them out of service.
John
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Post by nikeajax on Oct 2, 2015 19:35:54 GMT -8
John, for the longest time we, here in the Bay Area, have what they refer to as the "mothball fleet". They were ships that had sat for decades just in case: BTW the USS Iowa was until not too long ago a part of it. scotthaefner.com/beyond/mothball-fleet-ghost-ships/I like the idea of your mothball fleet of tanks. I recall your saying something about the old AL tanks were what were needed to make your Nautilus work. It's up to us daring soles to preserve unique pieces of diving history. This brings to mid all the back and forth we had determining whether or not having vinyl lined tanks were safe. As my friend Jim Steele put it, it's a part of diving history that is virtually forgotten and there are very few surviving examples left. I personally feel that we should keep the old AL tanks in use, if just limited, because it keeps the history from being lost. How exciting would it be seeing someone use one of the old USD AL professional tank mated up with with a Calypso, was it a IV, like Richard Dreyfus used in the movie "Jaws"... at depth! I know that I would want to talk to said person, and Don would probably shove me out of the way just to pick his brains. People already think that diving is a dare devil sport, and 95% of the people who find out that I use gear that's older than I am think I'm 51/50 (a danger to myself and others). I like to keep my gear as safe as I can, which is why I belong to this forum, it's a part of a checks-and-balances for me... JB
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Post by surflung on Oct 3, 2015 5:30:09 GMT -8
I've had over night to think about it. 1 out of 2 is my personal failure rate for these tanks and mine are non-abused, well cared for tanks... 1 out of 2 failed... So far. It's simply not worth the extra effort and worry (to me) to keep the other one in service. I've got to let it go.
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Post by luis on Oct 3, 2015 6:36:14 GMT -8
Just a few facts.
After the tanks pass the high magnification visual and the Eddy Current Testing the DOT is still recommending extra precaution during the fill process for cylinder made out of 6351-T6.
This is an extra risk mitigation step taken for a cylinder with a “known safety problem”.
I have not seen the same "safeguard" recommendations for any steel cylinder (or newer AL cylinders), that includes steel 72's from 50's or 60's (or even 3A steel cylinders that were manufactured in the early 1900's).
AFAIK, The current recommended “suitable safeguards” for filling this old aluminum cylinders is the commercially available explosion proof filling stations designed to divert the energy away from the operator. Most dive shops do not own this type of filling stations (due to cost), it is most common in fire department filling stations (for other reasons).
The Eddy Current Testing (or any other NDT procedure) is not 100% reliable.
There are many reasons why an NDT (Non-Destructive Testing) process is not 100% reliable. This could include equipment error, human error, improper tracking of data, and a variety of other potential errors in the process. I am aware of two specific cases were the cylinders passed hydro test, followed by a high magnification visual inspection, and then followed by Eddy Current Test. No cracks were found in either case (one here in Maine and one in Rhode Island). In both of those cases the cracks were detected during the filling process a short period of time after the inspection. Neither case developed into a catastrophic ruptured, but both are too close for comfort.
I know the owner of one of the shops very well and have a lot of respect for their work and testing procedures.
It is up to the owner of the cylinder and the filling station operator to make a the decision. It is hopefully an educated decision and it will hopefully take into account the benefits, the probability of risk, and the consequences.
If you want you could even do a risk matrix analysis. If you did a true risk matrix analysis, you will probably find that the consequences will drive the matrix into the red (even with a low probability of a catastrophic event).
Now for my own personal opinion: the consequences by far overshadow any potential benefit to continue filling this old cylinders. That is just my own personal decision.
BTW, if you read thought the referenced document, it may become obvious that the primary reason these older cylinders with a “known safety problem” have not all being retired out of service is economics.
“Avoided” in this context does not mean to eliminate. It is a term used in “risk management “ that refers to lowering the risk to a tolerable level.
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Post by SeaRat on Oct 3, 2015 7:59:01 GMT -8
Here are the twin 52s (steel, 1800 psig) which replaced my twin AL 50s. Here is the Risk Assessment Matrix that Luis has discussed above. It comes from the ANSI Z10, American National Standard for Occupational Helath and Safety Management Systems, 2005: Concerning these cylinders, the frequency would be either "Remote" or "Occasional," depending upon your view. Eb looked and had a 50% failure rate. My experience is not that high, but even at "Remote," the Risk Assessment Matrix states it is "Serious," and should have "High Priority Remedial Action." There are many different types of cylinders that have been used in the past. The AL 72 (2475 psig, the floaters) are one example, which I used for a while. There are the U.S. Navy twin 80s, made of an older process of AL which were never meant for hydrostatic testing; two sets were recently on EBay, and I did not publicize them (along with two DA Aquamasters, which some of us should pick up as they were the antimagnetic ones with gold-plating inside). These tanks should be kept, but if there is a danger (see the Risk Assessment Matrix above), they should be removed from service. I plan on diving my Dacor Nautilus CVS Monday, so as to remove most of the pressure from that tank ASAP. John
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Post by cnotthoff on Oct 3, 2015 8:30:49 GMT -8
John, for the longest time we, here in the Bay Area, have what they refer to as the "mothball fleet". They were ships that had sat for decades just in case: BTW the USS Iowa was until not too long ago a part of it. scotthaefner.com/beyond/mothball-fleet-ghost-ships/I like the idea of your mothball fleet of tanks. I recall your saying something about the old AL tanks were what were needed to make your Nautilus work. It's up to us daring soles to preserve unique pieces of diving history. This brings to mid all the back and forth we had determining whether or not having vinyl lined tanks were safe. As my friend Jim Steele put it, it's a part of diving history that is virtually forgotten and there are very few surviving examples left. JB Jay, My wife and I are off to Cozumel in a month. Scuba Club Cozumel uses all its failed aluminum cylinders as docking cleats and artificial reefs. There's your mothball fleet. We were in Vallejo last week. I didn't see the US Navy mothball fleet in Suisun Bay. Is it still there? My usual addition to this thread is that I have an original US Divers 2475 psi aluminum 72 that has passed hydro and visual eddy with a USD J-valve. I'd prefer to send it to someone here rather than the scrap yard. Cost of a hydro and shipping will send it your way. Good Dives, Charlie
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Post by luis on Oct 3, 2015 8:54:11 GMT -8
There are the U.S. Navy twin 80s, made of an older process of AL which were never meant for hydrostatic testing; John If you mean that they were not intended for DOT hydro test and requalification, that is correct. All Navy pressure vessels (actually all high pressure vessels) are / can / and should be hydro tested, both during initial pressure certification and during some established periodic inspection. The Navy would never approve a high pressure cylinder that was not hydro tested after initial fabrication and during periodic requalification. We would never grant a waiver on that one. I have several revisions of the Mil-Spec for this cylinders and they all contain the hydro test requirements. This cylinders were made out of 6061-T6. They were made from seamless pipe, using a spinning process commonly used in Japan by Asahi (a high pressure cylinder manufacturer). Asahi still makes DOT approved cylinders using that process.
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Post by luis on Oct 3, 2015 9:03:09 GMT -8
My wife and I are off to Cozumel in a month. Scuba Club Cozumel uses all its failed aluminum cylinders as docking cleats and artificial reefs. There's your mothball fleet. Good Dives, Charlie Hi Charlie, So did you know about Juan’s fatal accident last year at SCC? It happened in September of 2014. He was filling a 6351-T6 cylinder when it ruptured due to SLC. Juan was a very nice guy. They have since removed from service all the 6351-T6 cylinders. I believe no one in the island is using those tanks anymore. After the accident, SCC was not able to fill their own tanks for a long time. I have not talked to Henry in a while so I am not sure if their filling station is back on service. I am going to send you a private email. It is interesting that you are going to SCC in a month.
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Post by nikeajax on Oct 3, 2015 9:41:21 GMT -8
Charlie, last time I looked there were maybe three ships out there: I'm going to Napa on Tuesday and I'll make a mental note and report back, 'kay?
JB
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