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Inspecting Aluminum Scuba
Tanks
by Hans Petter Roverud
I do hydrotests and visual inspections for a dive store in Norway. I've seen quite a few cylinders. With few exceptions, those cylinders that are condemned fail the visual rather than the hydro. Aluminum is tricky and treacherous. It doesn't corrode from condensation. However, if it sees salt water, the ensuing damage is obvious in no time. We can stamp out and destroy those tanks without any further checking. According to regulations, we're not allowed to expose aluminum to acid rinsing in an attempt to salvage it. So unless the entire inside surface comes out spotless after a hot water rinse, that cylinder is condemned. No sleep is lost over corroded aluminum!
The really treacherous ones are old aluminum tanks that look OK. They have never seen salt water on the inside and present a flawless shiny surface. They may have been exposed to excessive heat, but this won't show. While the cylinder may still look great, metal fatigue can change the strength of aluminum alloys for a number of reasons. Theoretically, it will show as loss of elasticity during the hydrotest, but I wouldn't bet my life on it. I'm pretty much looking for a reason to condemn any old aluminum tank I test!
These days, the Norwegian Navy throws away cylinders after 10 years of service. A few years ago, a BC inflation cylinder exploded while being stored in a locker. The cylinder was in good standing regarding hydrotesting, yet it failed anyway. It was, however, made of aluminum and older than 10 years. Fortunately, nobody was injured.
Steel is different. Fatigue is less of an issue. When it's bad you can tell at a glance. Usually, the rust kills steel before it fails a hydrotest. Still, a badly rusted steel cylinder may prove to be OK after an acid rinse. Superficial rusting may look messy, but what you really want to know is whether it has progressed to pitting. The point is, what you see is what you get. There's rarely any doubt whether a steel cylinder will pass or not. The only good-looking steel cylinder I've condemned (since it failed the hydrotest) was produced in Germany in 1944. That was not exactly a good year for German industry since WWII had depleted supplies of decent quality steel! Even so, it took almost 50 years to develop fatigue.
Aluminum is more brittle. Old European cylinders have tapered valve threads that seal with a tape. The torque needed for proper sealing transfers as a constant sideways strain to the neck of the cylinder. I've seen aluminum cylinders with tapered threads suddenly develop hairline cracks. Luckily, the air vented rapidly without the valve coming off or the entire tank rupturing. It could be that the torque was excessive, but the point is that aluminum may crack during prolonged strain. Steel would yield, but the brass of the valve stem would be deformed long before the steel would have to yield beyond limits. Another point to remember is that the valve stem has to be isolated from the aluminum by means of tape or grease to avoid galvanic corrosion. This goes for straight as well as tapered valve stems. Brass in direct contact with aluminum means you will sacrifice the aluminum bit by bit due to galvanic corrosion.
Since metal fatigue is so hard to detect in aluminum cylinders, how about adopting the 10 year rule? The cost of condemning an old aluminum tank every 10 years is financially bearable. After all, the tank valve is half the price of a new cylinder. Besides, it's a lot more expensive to replace hands. This being said, I prefer aluminum tanks as side-mounts due to their buoyancy characteristics. I'm in no way suggesting that aluminum is out. I'm just saying that old aluminum tanks are dispensable.
Letter to Luxfer
by Skip Commagere (Owner of the Force E dive store chain)
The following is an excerpt of a letter that was sent to Luxfer in protest erroneous misinformation that Luxfer has propagated:
MS. KATHRYN GAMBOA|
Luxfer Gas Cylinders
Dear Kathryn,
I must apologize for not informing you the other day of who I am. By looking at the letterhead, you may now be aware that my company is the one that suffered the cylinder explosion in Riviera Beach Florida. You did a passionate job of defending your company and it's line of scuba cylinders. That defense, I'm sure, is based solely on information given to you by the company or it's representatives. The following will propose a different view and how I came to embrace it.
As you may be aware, on February 1, 1998 an aluminum tank exploded in our Riviera Beach scuba center. Chris Hawkins, the young man servicing our customer, was injured severely.
FEBRUARY 1, 1998
The Walter Kidde cylinder exploded in our store. Riviera Beach Fire Rescue and Police Departments responded to the scene, transported Chris to the hospital and secured the area. They reported the incident to the DOT.
FEBRUARY 2:
Darrel Donatto, Division Chief, Riviera Beach Fire Department called and said that he had reported the incident to the DOT and that they would probably be in touch. Mr. Donatto told me that he had found a Federal Emergency Management Special Advisory about Aluminum scuba tanks on the web. He faxed me a copy and gave me the web address. (http://www.fema.gov/home/usfa_2/alerts/firesrvc/rspa794.htm)
Later, Mr. Abis of the DOT called and said he would be down the following day to inspect the tank and our fill station. He asked what kind of tank it was and if it were in Hydro. I told Mr. Abis I thought the tank was made by Luxfer and that it had a current VIP. (The mate was a Luxfer with the same hydro and VIP dates).
FEBRUARY 3, DOT and LUXFER:
At about 12:30 PM I arrived at the Riviera Beach Fire Dept. Shortly after a Mr. William. Lee Birch of Luxfer Inc. and Mr. Scott S. Cairns, Luxfer's council arrived. I expressed some concern about the manufacture's attorney being present at a meeting designed to be a fact finding meeting by the DOT. Chris, the injured party, was not represented by council nor was Force-E. It became apparent to me, through conversation, that Luxfer was there solely to steer as much cause of the explosion away from their company as possible. Chris, (the injured man), was not represented by council and neither was Force-E.
When Mr. Abis of DOT arrived, I explained I was not comfortable with the presence of Luxfer and their council. I asked Mr. Abis what he planed to do from this point. He said he would examine the tank, ship it to Washington, and survey the damage at the store. I asked if he needed Luxfer or Force-E present when he examined the tank. He said he did not. I said that I would see him at the store and I left.
Mr. Abis arrived at our store and casually looked around. I asked him about the tank and he said he couldn't tell what kind of tank it was. He said he didn't think it was a Luxfer. This surprised the three of us that were there the day of the explosion. Abis said ".... It had some strange marks on it that I didn't understand." He assured me as soon as the tank got back to Washington, they could discover the make.
Still thinking it might be a Luxfer, I asked him if all leaks and explosions of aluminum tanks had come from the same alloy and possibly the same manufacture, and why hadn't DOT recalled the tanks. His answer was amazing. I wish I could give an exact quotation. I can't. The following is a close rendition:
Recall!? No no no. It's very political. These companies have lobbyist in Washington. It's not economically feasible. There are very few injuries and about seven million tanks out there. Luxfer would go bankrupt and then the only tank manufacture would be Catalina. The price of tanks would go way up. You don't want to see that do you?
I ask him how I could explain that to Chris and his family. He had no answer.
Perplexed and concerned, our store manager contacted the hydro facility that had previously tested the exploded tank and the mate that we had on hand. They said they had tested three tanks on the same date for the customer. Two were Luxfer and one was a Walter Kidde. One serial number matched the Luxfer tank and the first four numbers(all we had,) of the exploded tank matched the numbers of the Kidde.
THE PRESS RELEASE:
No Later than February 2 Luxfer released the following statements on the Net and sent it to several publications. The first release was not altogether accurate.
(Taken from Luxfer's website)
SCUBA CYLINDER RUPTURES IN FLORIDA
...Although, it is not known at this point whether a Luxfer cylinder is involved, the company has dispatched its senior investigative officer to gather facts, meet with all parties involved and render any assistance possible. This news bureau will be updated periodically as confirmed facts become known to the company. It is not Luxfer's policy to disseminate any information that has not been verified for accuracy.
Inaccuracies or omissions in this statement are as follows:
Luxfer also dispatched their attorney. If they came to "render assistance" to Chris, DOT, or Force-E, we saw no evidence of it. Luxfer's policy not to disseminate information unless verified rings hollow.
The second release was not just inaccurate, it was spun to send the reader's conclusions in the wrong direction. After reading the release, many people thought Chris should have recognized a bogus cylinder and refused to fill it.
RUPTURED RIVIERA BEACH, FL, SCUBA CYLINDER WAS UNAUTHORIZED FOR USE
...Experts investigating the explosion at the Force E dive store in Riviera Beach, FL, last Sunday, revealed today that the cylinder is not authorized for use by the federal Department of Transportation and was probably not made by any established manufacturer, such as Luxfer or Catalina.
Inaccuracies or omissions in this statement are corrected as follows:
The cylinder is a Walter Kidde, an established manufacture. The tank was manufactured in 1984. It had a current hydro and visual inspection. It was authorized for use by DOT. Luxfer was informed of this possibility on February 4 and confirmed a few days later. As of February 27, the news release is still being offered as fact.
At the time of the release, Mr. Abis of DOT was not sure of the manufacture because some identifying marks were scuffed off as a result of the explosion. When contacted for comment, Mr. Abis said that he never said that the tank was not approved for use.
LUXFER'S ACTIONS AND ATTITUDE SPARK SUSPICION.
I was shocked at Luxfer's stance and attitude in this matter. Why was Luxfer willing to slant the facts in a news release? Why wouldn't Luxfer's Product Compliance and Safety Manager answer questions? Why did Luxfer feel it necessary to fly an attorney in for the investigation? Why did Luxfer change the alloy in their tanks? The deeper I looked, the more questions I had.
THE FACTS WE COULD FIND
In October of 1987, Mr. Ament, Vice President - Sales for Luxfer wrote "....the following to provide some background information on the problem reported by the Department of Transportation in the July 10, 1987 edition of the Federal Register. In 1982 and 1983 some of the cylinders produced were made from material which met all the specifications, but which was supplied from other than normal sources. It was subsequently determined that cylinders produced from this material had a greater potential for developing leaks....in 1983, Luxfer eliminated the purchase of all this material and tightened the specification on subsequent purchases. Also, because crack potential is effected by stresses, a great deal of effort has been expended in controlling and improving the inside surface finish of Luxfer's cylinders... ...tests both in laboratory and with fully charged cylinders in a bunker confirm that these changes have eliminated any potential for cracking". As to the tanks produced in 1982 and 1983, "....fracture mechanics analysis and results from experimental tests from highly pressurized cylinders confirm that if a crack develops, the failure mechanism will be a very slow leak".
On June 4, 1994 a Luxfer cylinder exploded at Scuba Sports Dive Store in North Miami Florida. Arnie Hubber was seriously injured. He lost his right thumb, broke his fight arm and left leg among other injuries. The cylinder had a current hydro(less than two years old) and VIP. Subsequently, following statements were sent to fill station operators by The Miami Association of Dive Operators shortly after the incident. "As you may know, Luxfer has been aware of a certain percentage of cylinders manufactured in the years 1982 and 1983 which developed neck cracks. Do not refill any Luxfer cylinder which has an original hydro date of 1982 or 1983."
June 21, 1994 Debbie Reed, Customer Service Manager for Luxfer wrote; "There has been an increase in quick filling cylinders. Luxfer, and much of the diving community, views quick filling of diving cylinders as an unsafe practice. Luxfer recommends that diving cylinders be filled at the rate of 300 to 600 psi per minute. Quick filling of cylinders does not allow time for the filler to properly inspect for leaks, as recommended in the attached technical bulletin. Luxfer recommends that these diving procedures be strictly enforced at all locations". She goes on to say, "Periodic inspections are critical to the continued safe use of high pressure cylinders. Failure to do so properly could lead to cylinder failure resulting in serious injury or death".
July 26, 1994. Department of Transportation safety advisory report detailing the explosions that had occurred with tanks made from the 6351-T6 alloy.
MAIN POINT OF CONCERN:
What ever the alloy, the vast majority of cylinders that fail visual and electronic inspection are old. So far, from conversations and documentation, over eighty percent are fifteen years old or more. Almost the remainder are greater than ten years old.
SUMMATION:
It would seem that Luxfer is doing everything it can to distance itself from the liability of an inferior alloy. "Tank abuse" was unheard of before June 1994 when a Luxfer cylinder tore the thumb from Arnie Huber. Suddenly, Luxfer was saying that filling tanks faster than 300-600 psi per minute was dangerous because it was too fast to check for leaks. They also said that filling a Luxfer cylinder beyond the stamped working pressure would abuse the tank. You told me that Luxfer is claiming the tank that exploded in ‘94 was abused. I was told by you "....the last visual inspector should have seen the crack that must have been there, perhaps for years".
I think the biggest problem with tank safety is Aluminum alloy 6351-T6. Not that better visuals wouldn't help safety. But, there are only two common links to aluminum tanks that explode and suffer SLC. Age and 6351-T6. Virtually every aluminum tank made before about 1989 was made of 6351-T6 material. The one exception is Catalina cylinders.
In 1982 and 1983, Luxfer made some 6351-T6 cylinders with even more lead than was called for. That made the cylinders even more brittle. These cylinders are the ones that first started to leak. Luxfer tested them in 1989 and announced that the tanks would only leak. They were wrong.
The tanks started to explode. In 1994, Luxfer announced that some of their tanks had been mistreated. Abused is the word they used. Horror upon horror some tanks were being filled to 3100, 3200 and yes, hang your head in shame, some saw more than that on a hot day. Luxfer said "that's tank abuse!!' I agree, filling scuba cylinders to 10% above ratings shouldn't happen. Not because its somehow going to damage the tank. That kind of fill could effect the regulator/tank connection.
When more leaks and cracks started showing up on cylinders with current Visual Inspections, Luxfer said we need better equipment. Now there is an electric eddy current machine called a Visual Plus. This machine can detect unseen cracks. Luxfer and/or its parent company have more than a slight financial interest in it's manufacture. Their other interest seems to be finding bad tanks and getting them off the street.
At first blush, it sounds like a noble cause. Turn it around and Luxfer has a lot of bad tanks hiding out their and the dive operators are supposed to seek them out. The implication is, if a tank explodes and hurts or kills someone, It's the dive operator's fault for not finding it in time.
I sound like I'm beating up Luxfer here, but they are the only one I've seen trying to change the sport to fit the capabilities of their old equipment. Walter Kidde Co. Built tanks out of the same stuff but they're not building tanks anymore. They've been very quiet. Luxfer, for the last decade, uses a better alloy. I think they're afraid to take the blame for the bad stuff. Catalina, the only other company producing aluminum diving cylinders, never used 6351-T6 alloy. They always used what Luxfer uses now.
Tanks have gotten "good" fills since U.S Divers was a glint in Cousteau's eye. The steel tanks used to have a little + on em' just to make you feel good about going 10% over.
Do you think a billion dollar tank company didn't do market and technical research? Do you think that Luxfer was unaware of common practices with their products for 20 years?
Luxfer doesn't want any tank filled in less than five minutes or they'll scream "TANK ABUSE". They should show us the data. I have asked for it.
I say, give us tanks that don't blow up. Is it too much to ask?
The problem has been creeping up on us at about the same rate as the 6351-T6 tanks get older. As the pool of old tanks get older, failure rates go up.
Could it be that Luxfer Cylinders doesn't want to go to a Group board meeting and say; "we have a million and a half scuba cylinders out there and a bunch of ‘em are cracking. We don't know why and we have no way of telling which ones will go bad. If they explode, people will be hurt and some will die. Should we recall em?"
If they did go before the Board, could the answer have been; "No. Stonewall it. Spin the fault to the customer and the fill stations. Develop some way to find these bad tanks faster. Check our insurance. Remember, always look like the good guy. You can spend money if you have to but always keep the bottom line in mind".
What a cynic. History will do that to you sometime. Please pass this letter up the chain. Please have Luxfer show me some real facts produced by real scientists and true statistics. I'd like to know the following:
I'm only interested in DOT approved aluminum scuba cylinders that have a working pressure of greater than 2100 psi and less than 4000 psi.
How many cylinders in each of the above years did Luxfer distribute to the United States scuba diving market?
How many Luxfer cylinders have exploded? What was the first hydro date? What year did they explode? What was the cause of the explosion and what data do you have to support your hypothesis? What is the projected cycle life of cylinders made of 6351-T6? How about 6061-T6? What data and/or tests has Luxfer conducted or sponsored to show how and why (SLC) manifests itself? How long or how many cycles does it take? What tests has Luxfer conducted that supports the recommended fill rate? Please show us the data.
What data does Luxfer have that filling a cylinder less than 10% over working pressure has an adverse effect on tank life? How much effect? I know that there are some cylinders in the market that will not perform as expected. Aluminum is a relatively new material in this use. I just want to know what you know. We all had a problem with old steel cylinders a couple of decades ago. Aluminum captured the market. Old steel cylinders went away and so did the problem. Now, old aluminum seems to be breaking down. Maybe old is not so good for high pressure cylinders.
What are the odds? Hell, they're astronomical until you look at how few people man the fill-stations of this country. There are only about 2000 commercial fill stations in the US. I would guess that less than 10% do over 80% of the fills a year. In the last four or five years some have exploded and who knows how many have been discovered leaking or cracked. We are in the precarious 10%. Give us the facts. We'll (the dive stores and boat operators) come to a reasonable decision. Who knows, it may even solve some of Luxfer's problems.
Sincerely, Thanks
Skip
If you would like your scuba safety article to appear here as well, please submit it to me, Dennis Hawkins (Chris's uncle), for consideration.
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