An expensive education

[The Chairman]

Luxfer...




From a Luxfer Seminar at the February 2001 DEMA Show

Luxfer recently responded to frequently asked questions about sustained-load cracking (SLC) in aluminum scuba cylinders made of 6351 alloy.

1. What is sustained-load cracking?

SLC is a metallurgical phenomenon that occasionally develops in cylinders made of 6351 aluminum alloy, as well as in other types of pressure vessels and structural components under stress for sustained periods of time.


SLC has occurred in cylinders manufactured by various companies, including Luxfer.


Cylinders that have been mechanically damaged, over-filled or abused are more susceptible to SLC.


SLC is not a manufacturing defect; it is a phenomenon inherent in the metal itself.


2. How quickly do the cracks grow?

Very slowly, as extensive research by Luxfer and outside laboratories has shown.


No scientific evidence supports rumors and claims of "fast crack growth."


Cracks typically take six or more years to grow large enough to cause a cylinder leak.


Because SLC growth is so slow, properly trained inspectors have adequate opportunity to detect cracks during the normal requalification process.


3. How many aluminum cylinders have exhibited SLC?

Out of a total U.S. population of 1,073,000 Luxfer scuba cylinders made of 6351 alloy, only 1.25% have exhibited SLC.1


Out of Luxfer's total 6.1-million U.S. population of 6351-alloy cylinders, the SLC rate is slightly less than 0.37%.


While we do not have complete statistics on cylinders manufactured by other companies, industry experts estimate that out of a worldwide population of more than 30 million 6351-alloy cylinders, far less than 1% have exhibited SLC.


4. Which types of cylinders are most susceptible to SLC-related ruptures?

Any type of cylinder manufactured from 6351 alloy could conceivably develop a sustained-load crack over time if subjected to certain conditions.


However, a cylinder is more likely to rupture in applications where pressure is higher and where overfilling and abuse occur more often.


Historically, the applications most susceptible to SLC-related rupture are scuba and SCBA (life support).


5. Are SLC-related scuba tank ruptures widespread?

No. Of the more than 30-million all-aluminum cylinders manufactured by various companies over the last 30 years, only 17 SLC-related or suspected-SLC ruptures have been reported to regulator authorities around the world.


Of these ruptures, eight have been scuba cylinders. Four occurred in the United States, and the remainder occurred elsewhere in the world.


Let's look at the actual record...


Aluminum scuba tank ruptures

DATE LOCATION LISTED CAUSE INJURY? MANUFACTURER
Jun-94 Miami, FL SLC Yes Luxfer
Jan-98 Corlette, NSW SLC No Luxfer Australia
Feb-98 Riviera Beach, FL SLC Yes Walter Kidde
Aug-98 Tairua, NZ SLC Yes Luxfer
Dec-98 Tampa, FL Not determined No Luxfer
Apr-99 British Colombia SLC No Luxfer
Mar-00 Key Largo, FL Not determined Yes Walter Kidde
Jun-00 Miyako Is. Japan SLC No Luxfer Australia




6. If there have been so few SLC-related cylinder ruptures, why is there so much alarming information about them on the Internet?

A great deal of misinformation and exaggeration about SLC is attributable to rumors and inaccurate reports spread by word-of-mouth and the trade press, but especially by the Internet, where the proliferation of inaccuracies is widespread and essentially unregulated.


7. Why is it necessary to have my 6351-alloy cylinder inspected with an eddy-current device?

When properly used, eddy-current devices contribute significantly to early detection of hard-to-see sustained-load cracks.


However, an eddy-current test is not a replacement for a diligent visual inspection by a properly trained inspector.


Eddy-current devices are tools to enhance proper visual inspections.


8. How do I know if the person inspecting my cylinders is properly trained?

Luxfer recommends taking your cylinder to an authorized Luxfer service center or to an inspector trained by Professional Scuba Inspectors, Inc. (PSI) or the Association of Scuba Service Engineers & Technicians (ASSET).2


It cannot be overemphasized that the quality of inspection is far more important than the frequency of inspection! An untrained or improperly trained inspector can look at a 6351-alloy cylinder numerous times without detecting SLC.


9. How do I know if the person inspecting my cylinder is properly trained?

Unfortunately, many untrained or improperly trained technicians continue to inspect cylinders, and no uniform standards for inspector training and certification exist among regulatory authorities around the world.


Luxfer is working with industry groups and government agencies to help establish such standards.


10. How can I tell if my Luxfer cylinder is made from 6351 alloy?

The easiest way is to check the original hydrostatic test date stamped on the cylinder crown.


Luxfer manufactured 6351-alloy cylinders during the following periods:


United States: 1972 through mid-1988


England: 1958 through 1995


Australia: 1975 through 1990


After these dates, Luxfer began making cylinders from a proprietary 6061 alloy, which is not susceptible to SLC.


11. If Luxfer 6061-alloy cylinders are not susceptible to SLC, why has Luxfer exchanged 6061 cylinders that have been reported to have cracks?

After the introduction of eddy-current technology, Luxfer received reports of cracking in 6061-alloy cylinders. We accepted returns on about 1,200 of these cylinders to conduct extensive tests. Not a single cylinder was found to be cracked.


On Luxfer 6061-alloy cylinders, eddy-current devices sometimes show harmless "indications" that lead to "false-positive" readings for SLC.


12. How often should my Luxfer 6351-alloy scuba tank be inspected?

DOT requires requalification (hydrostatic retesting and visual inspection) of all aluminum scuba tanks every five years, regardless of alloy.


Both the DOT and the U.S. scuba industry recommend an annual visual inspection for all 6351-alloy scuba tanks. Luxfer supports this recommendation.


For its 6351-alloy tanks, Luxfer has established a manufacturer's requirement for a visual inspection, including an eddy-current test, at least every 2.5 years.





FOOTNOTES:

1Statistics are current as of February 1, 2001; statistics are subject to change.

2Telephone PSI at 425-486-2252; e-mail: psicylinders@msn.com. Telephone ASSET in England at 01524 381831; e-mail: admin@scubatechnician.com.

 

[roakey]

All Luxfer asks is that you fill out some information and you can get a FREE guide to inspecting AL cylinders.

See: http://www.luxfercylinders.com/americas/product_info/life_support/safety_first/orderbooks.asp.htm

Roak

 

[Green_Manelishi]

A word of caution about preparing to play "hardball" with your
LDS ...

If that is the only LDS in your area and you make it onto the s***-
list you'll not be welcome in the shop and/or the shop will charge
you for everything. You will HAVE to pay, or you will have to shop
via mail. If it is NOT the only shop and you can take your business else-where then take appropriate action.

 

[Bob3]

If you don't want to give Luxfer all the info they're asking for, here's the URL that goes directly to the file: http://www.luxfercylinders.com/americas/product_info/scuba/guide_video/scubaguide.pdf

It's a honker, coming in at 20 megs. It could've been nicely done at around 1 meg, but Luxfer doesn't seem to give a hoot about the large size.

BTW, ALL aluminum tanks will fail if cycled enough times, its just the nature of the metal.
Happily, the required number of fill cycles cannot be realistically attained in "real life".

 

[MrMrEZG]

i will not fill any tank that i feel is unsafe. if the owner of said tank feels that i am wrong then he can get it filled by some one else. when tanks explode it happens at the fill station and it is the fillstation operator who is injurred/killed. If a certain alloy has a reputation for failing then that makes it, in my eyes, unsafe to fill.

Note "sustained" implies quite a bit of time.

at the least tanks made with the 6351 alloy are 15 years old, i wuold classify that as "quite a bit of time"

the truth is that not all of those tanks are "bad" however, they have a failure rate that justifies my refusal to fill them. You can be certified by 1001 different agencies to inspect tanks, but untill you are the one who is filling them you don't know what you'd do.

Now tom you should get it in writing from your LDS and try to get your money back.

 

[roakey]

MrMrEZG,

Are you PSI trained? If so, why do you choose to ignore your training? Do you not trust your abilities to find a crack? If so I hope you're not advertising that you can do inspections!

From the president of PSI on SLC:

http://www.psicylinders.com/message.html

Take a couple minutes to read it. It’s quite informative.

For instance, there’s been only 17 failures out of over 25 MILLION cylinders (this includes SCBAs). I assume you don't drive, fly, or for that matter SCUBA dive since the risk is far, far greater for those activities than for a 6351 failing.

When do you start refusing to fill cylinders bought from other shops because they might be "dangerous?" That'll boost your cylinder sales for sure!

"at the least tanks made with the 6351 alloy are 15 years old, i wuold classify that as 'quite a bit of time'". I guess you don't understand (maybe you’re not PSI trained since they go over this in the class). The cracks DEVELOP over a long period of time. I've looked at a lot of 6351 cylinders, some over 20 years old that have no cracks in them.

Perfectly good cylinders. Even according to the regulating agency. Even according to the organization that [I assume] trained you to do inspections.

So, now armed with the facts, are you going to change your store policy, or can we assume that this is merely a ploy to sell cylinders to your more gullible clients?

Nothing ticks me off more than ignorance and fear mongering, and that’s the only thing behind this “6351 scare” since the data doesn’t support such a reaction.

Roak

 

[buff]

17 failures out of 25 million tanks?......I'll take my "chances". I laugh at the probability!!-my chances are better that I'll win the state lottery(I would have to buy a ticket first)-or even better that I'll get hit by a car while walking to church.
You deal with probablity of dangerous events every day( see crossing the street example)-it's just in this case you are very aware of the odds. Besides, as an inspector, if you can't spot a crack in a tank that is known to have a slighty higher rate of cracking then when CAN you spot a crack?? That is what the inspection is for-to look for structural integrity-not just to rubber stamp the inspection so the LDS can get a fee-or sell a new tank.

Mike

 

[TwoBitTxn]

Boy did I open a can of worms or what.

I am getting part of my money back. I am an honest believer in Caveat Emptor (Let the buyer beware). I did not totally know what I was getting. I should have asked more questions. I have been educated.

Thank you all for the information and encouragement. Everyday I learn how ignorant I really am.

Tom

 

[roakey]

Well Tom, you did say you wanted an education.

Bottom line: If your shop won't fill a 6351 cylinder, that tells me that they don't trust their own ability to do a good inspection on ANY cylinder. Finding defects in cylinders is the entire reason that they took the PSI class for and the entire reason for doing VCIs in the first place!

What next, "steel can rust, so we're not filling steels?"

SLC can be found by sight easily YEARS before the cylinder lets go. You get several shots at finding a crack; it's not like the cylinder is perfect one VCI and catos the next month.

Roak

Ps. Ed Kasten, PSI's training director (if I remember his title correctly) was both my original PSI instructor as well as my renewal instructor. When I mentioned something along the lines of "I'll stay away from 6351s unless I have an eddy current tester" he basically ripped up one side of me and back down the other with the same arguments that I'm presenting here. I listened. I wonder if the folks from the shops in here that refuse to fill 6351s will listen too? If they’re PSI trained all they have to do is pick up the phone and call their PSI instructor, or Bill High if they want to and ask as many questions as they’d like about 6351.

 

[MrMrEZG]

I appearently did not realize that if ROAKEY declares that a threat doesn't exsist, then there is no threat.

so roakey I know of plenty of smokers that are still living does that mean that it is safe to smoke?

I also know divers who have exceded recommended ascent rates, so does that mean, according to your method of reasonning, that a diver can ascend as rapidly as he wishes?

as you can tell both of these statments are totally ridiculous and so is roakey's notions of how you should ignore any and all warnings and a tank that is dangerous. I also would like to point out the fact that he does not fill tanks, I guess he feels that it's a job for the "monkeys", and who cares if a tank blows up and kills one or two of them as long as he does not have here that his tank cannot be filled.