Tanks...which ones can't be re-hydro'ed?

[Rick Christ]

Here's the best policy:
Don't fill 6351 cylinders, and if you own some, ditch 'em.

You better ditch your 6061-T6 also. the SLC problem in them is only going to get worst. your one of the ones that have more knowledge about cylinders then the engineer, scientist and metallurgist at the manufacturer, DOT, PHMAS and OHSA.

 

[DA Aquamaster]

I believe that this is going to be revisited because the issue of the 6351-T6 has now been absorbed into 49CFR 180.209m. I do not believe that a DOT Requalifier will be allowed to pick and choose what part of the CFR that they agree with and what part they don't want to follow. This would be absurdly foolish and the DOT would loose all control

A test facility that fails a tank has t keep records and those can be viewed by the owner fo the tank. If a tank passed the inspection but was failed and rendered unusuable by the tester, they are going to owe someone a new tank.

At the same time the test facility is required to retain the test records so that in the event the tank fails, the test records can be reviewed by the DOT. If a tank explodes, the DOT will look up the test records and if the tank was properly inspected and passed the test, the test facility is not going to be liable for returning the tank to service. So there is in effect no down side to a test facility doing the test per the CFR's, but there is a downside to them doing one to their own standards.

One can argue that a business can refuse servcie to any customer but that is not always true and can potentially result in civil liability for refusing to test 6351-T6 alloy tanks as their refusal as a DOT approved test facility may result in uneccesary expense to the owner of the tank (who has to ship it elsewhere for testing).

Quite frankly as there are millions of 6351 T-6 tanks still in service in the medical O2, SCBA, Scuba and CO2 service industries, a test facility is very unlikely to refuse to test a 6351-T6 tank as it is a big chunk of their business and they get paid whether it passes or fails.

Dive shops are another matter given that many have what amounts to a very ignorant approach to the whole 6351-T6 alloy issue and also potentially gain in terms of tank sales.

Before anyone says it, believe me, I know how small the markup and profit margins are on tanks, but shops have to stock them to have them available for divers who want to buy one now and do not want to wait while you order one or pay the expense in shipping one or two of them. And once they are in stock they are a time limted item as a hydro date greater than a year old diminsihes their value. The end result is there is still pressure to stock and sell tanks, and owners of 6351-T6 tanks a shop refuses to fill are still an attractive target for a tank sale.

I agree with Rick that the vast majority of failure of 6351-T6 tanks are in the form of leaks, not catastrophic failures. There have in fact been no SLC related catastrophic failures in properly inspected 6351-T6 alloy tank failures since eddy current protocols were implemented. The current DOT regs are based on that and the overwhelming weight of evidence that crack propogation is so slow that it cannot progress from the point where it can be detected to the point of failure in less than 5 years (the requalification interval). The scuba industry standard of an eddy current inspection every year, adds 5 more tests as additional insurance (6 if you count the redudant VIP the tank gets from the dive shop when it comes back from hydro.)

I also agree with Rick that it is inevitable that cracks of some type will show up in a very small percentage of 6061-T6 tanks and that they will begin to occur as some of these tanks now exceed 25 years of age. Unfortunately that will feed the "don't fill any tank older than (pick one) 10, 15, 20 or 25 years of age" hysteria.

 

[oxyhacker]

They are allowed to all ready, and have been all along. There's a big difference between picking and choosing what tanks you are going to accept for inspection, and picking and choosing what parts of the CFR you want to follow once you do accept the tank for testing. Sort of like how a Ferrari dealer can be a state licensed auto inspection station, but that doesn't mean it has to service Yugos. I've had several hydro shops over the years that test almost exclusively industrial tanks refuse to do my alu 80s because they were uncomfortable with the higher test pressure!

Re SLC and 6061, there is catastrophic fast-propogating SLC, and the plain ol' slow kind that most highly stressed aluminum applications are prone to. No one has ever said the 6061 can't develop stress cracks, but the DOT and the tank manufacturers tell us that the 6061 tanks are "LBB" - leak before burst - and so any cracking will reveal itself by leaking long before it becomes dangerous as the grain pattern of the 6061 alloy doesn't encourage runaway straight-line cracking as can occur with 6351. Time will tell us if this is true, but there are some pretty old 6061 tanks about by now, and I haven't heard of any bursting.

I believe that this is going to be revisited because the issue of the 6351-T6 has now been absorbed into 49CFR 180.209m. I do not believe that a DOT Requalifier will be allowed to pick and choose what part of the CFR that they agree with and what part they don't want to follow. This would be absurdly foolish and the DOT would loose all control

 

[Rick Christ]

A test facility that fails a tank has t keep records and those can be viewed by the owner fo the tank. If a tank passed the inspection but was failed and rendered unusuable by the tester, they are going to owe someone a new tank.

Not right, the Retester must keep his log for the lenght on the test(five years in most cases)If the Retester has stared tanks they will need to hold those logs for ten years. That log info does not have any mandate to be shared with the owner of the tank. the only info the the Retester must share is, when condemned the retester must notify with a letter of the condemnation.

Quite frankly as there are millions of 6351 T-6 tanks still in service in the medical O2, SCBA, Scuba and CO2 service industries, a test facility is very unlikely to refuse to test a 6351-T6 tank as it is a big chunk of their business and they get paid whether it passes or fails.

This is not the situation, many Retester are rejecting service on 6351-T6. This is what I was refurinng to. I do not believe that a DOT Requalifier will be allowed to pick and choose what part of the CFR that they agree with and what part they don't want to follow. This would be absurdly foolish and the DOT would loose all control.

Here is a little note, If the DOT Retester rejects service on your 6351-T6. They are mandated by CFR, that they give you a letter of rejection. I dont think many of them are following that.

 

[Rick Christ]

They are allowed to all ready, and have been all along. There's a big difference between picking and choosing what tanks you are going to accept for inspection, and picking and choosing what parts of the CFR you want to follow once you do accept the tank for testing. Sort of like how a Ferrari dealer can be a state licensed auto inspection station, but that doesn't mean it has to service Yugos.

You do not understand what I am saying, There are many Retesters that are testing scuba but they are rejecting 6351's also. My point is, with DOT's rule on eddy current and that 6351s are ok to put back into service. If you test 6061 what is the idea behind rejecting 6351 alloy and can the retester make that distinction because DOT has put this issue to bed. The retesrter that are rejecting 6351s are saying that they know better then the DOT, what is safe and I beleive the DOT is not going to agree well with that.

I've had several hydro shops over the years that test almost exclusively industrial tanks refuse to do my alu 80s because they were uncomfortable with the higher test pressure!

They may be only a low pressure shop

Re SLC and 6061, there is catastrophic fast-propogating SLC, and the plain ol' slow kind that most highly stressed aluminum applications are prone to. No one has ever said the 6061 can't develop stress cracks, but the DOT and the tank manufacturers tell us that the 6061 tanks are "LBB" - leak before burst - and so any cracking will reveal itself by leaking long before it becomes dangerous as the grain pattern of the 6061 alloy doesn't encourage runaway straight-line cracking as can occur with 6351. Time will tell us if this is true, but there are some pretty old 6061 tanks about by now, and I haven't heard of any bursting.

Where are you getting this, catastrophic fast-prorogating SLC, and the plain ol' slow kind. Who at the DOT and what tank manufacturers have told you this? I talk to the DOT on a regular basis and speak to most of the tank manufacturers. I have never been informed of these findings.

The original idea was that the lead content in the 6351 was the cause of the cracking, but now that we are finding cracks in the 6061-T6 (the lead was taken out of 6061, FYI) that thinking does not stand up and the industry must rethink this issue. I have some reasons to believe that many of these cracks are stemming from poor QA in the manufacturing process. Many of the cracks are showing up from valleys in the radius of the tank. This may be a problem with keeping the heat consistent when the radius and neck are formed. Now this is just a hypothesis at this time.

 

[DA Aquamaster]

Not right, the Retester must keep his log for the lenght on the test(five years in most cases)If the Retester has stared tanks they will need to hold those logs for ten years. That log info does not have any mandate to be shared with the owner of the tank. the only info the the Retester must share is, when condemned the retester must notify with a letter of the condemnation.

As a practical matter you can't conduct a test, condemn a tank and then refuse to show the test data to the owner of the tank. DOT regs, public information, etc aside, if nothing else, the customer will force you to prove the tank failed by producing the records when they sue you for the cost of the tank in small claims court.

If the tester did a valid test, they have nothing to hide and it takes less than 2 minutes to go over the test results with the customer.

And Comic Sans Serif is a pita to read...

 

[Rick Christ]

As a practical matter

you can't conduct a test, condemn a tank and then refuse to show the test data to the owner of the tank....

OH yes they can​

DOT regs, public information, etc aside, if nothing else, the customer will force you to prove the tank failed by producing the records when they sue you for the cost of the tank in small claims court.

If the tester did a valid test, they have nothing to hide and it takes less than 2 minutes to go over the test results with the customer.

And Comic Sans Serif is a pita to read...

1. Show me the DOT Regs. (I have 49CFR 100-185) in my hands right now.

2. The log of the Retester is not public information.

3. Small claims court does not have subpena power.

4. The customer would have the burden of proof that the test was invalid

5. How would the customer proof this? the only person in that room that has the knowledge to determine the validity of this test is the Retester. The judge doesn't. The customer doesn't. You talk like you have the ability to determine if a test was invalid. Are you a Authorized DOT Cylinder Retesters. I dont think so. Did the customer witness the test, NO.

6. It is impossible to determine that the tank did not fail the test without an engineer/metallurgist doing a destructive analysis. This may cost the customer thousands.

7. The Retester could file a counter suit for his time lost. Somewhere about $200-250 per hour, port hole to port hole.

How much is the customer going to spend $2000-3000-4000-5000-$10000 in this fight.
Get real

 

[captain]

As a practical matter you can't conduct a test, condemn a tank and then refuse to show the test data to the owner of the tank. DOT regs, public information, etc aside, if nothing else, the customer will force you to prove the tank failed by producing the records when they sue you for the cost of the tank in small claims court.

If the tester did a valid test, they have nothing to hide and it takes less than 2 minutes to go over the test results with the customer.

And Comic Sans Serif is a pita to read...

My tester gives me a copy of the test results for my records. Everyone should ask for a copy of the test results and have a basic understanding of what they mean.

 

[oxyhacker]

The fast-propogating SLC was something the Florida folk came up with at the time of the Force E explosion. Basically, they were claiming that since they had put a sticker on the tank, and it burst before the sticker expired, that it must mean SLC cracks could propagate much faster than hitherto believed. Others found a simpler explanation, and the DOT and tank manufacturers never endorsed the notion.
But the differences between how 6351 and 6061 handle cracking, and the principles of LBB construction are well known in the industry, and any DOT tank person or tank manufacturer's engineer should be able to tell you about it. Basically the difference between ripping a piece of nylon cloth, and a piece of ripstop nylon.

Oh re the shops that refused to test my tanks, they were, of course, not LP shops, otherwise they wouldn't have been testing CO2 and oxy tanks. They were just old, hidebound shops that did thousands of 1800 and 2250 psi tanks, didn't ordinarily do anything higher, and got nervous anytime the gauge started getting above 4000 psi. Irrational, perhaps, but their privilege. And perfectly OK with the DOT.

Where are you getting this, catastrophic fast-prorogating SLC, and the plain ol' slow kind. Who at the DOT and what tank manufacturers have told you this? I talk to the DOT on a regular basis and speak to most of the tank manufacturers. I have never been informed of these findings.

 

[weaserm99]

The shop i work for stopped testing the 6351 tanks back in 2007. We did this after numerous shops that we were in contact with did the same thing, my boss then called every local shop to tell them what we were doing and if they wanted to test the tanks we would gladly send the 6351 tanks to them. One shop in the area decided to follow suit with us. We also offer a $50 trade in, we take the old take and you get a brand new one for $50 less. As of today i checked the records and roughly 50 or 60 people have decided to take the trade in value for the tank. We are not lazy for not wanting anything to do with these tanks and before someone says that we are just trying to sell more tanks, $50 off is roughly selling the tank at cost, we receive maybe $20 in scrap for a tank at a local junkyard, now add in the cost of my boss paying me to load the tanks into a truck, driving to the scrap yard, unloading the tanks at the yard, getting the check and then driving back to the shop it is back to barely breaking even. Every person that comes through our door with these tanks is given the facts about these tanks. And yes it is true that most of the accidents with these tanks have occurred when someone was filling the tank but when the day comes that someone gets killed while diving with these tanks it will be all over CNN, fox news, abc, nbc and cbs, the dive industry will take a huge hit in terms of people getting certified. And besides where else can you buy something and it lasts for over 20 years.