Following on from recent controversy on tank failures we interview prominent members of the dive industry, and manufacturers, for their thoughts.

Are Aluminium Cylinders Safe?

Interview with Brian Horton and Ian McIntyre, Air Technology, Auckland

By Dave Moran

How long have you both been involved in the dive industry filling and testing cylinders?

We’ve been involved for over 20 years in making and selling hydrostat test equipment, and we’ve had our own test station for ten years.

Have you seen major faults starting to appear in tanks recently that you didn’t see 20 years ago?

We’ve seen an increasing number of cracks appearing in the necks of aluminium cylinders. We still see some problems with rusting of steel cylinders.

When you pick up these cracks, is it during the normal two-yearly visual test?

We mainly pick them up on the visual inspection prior to the hydrostat test, or the alternate year for the visual inspection.

Some people are saying that during the period between hydro testings they’re finding cracks are appearing. Have you had that problem?

Yes, it’s a fairly common problem. There is a difference between Australia and New Zealand in the test procedure: in Australia it is mandatory to do a visual inspection after the hydrostatic test, while in New Zealand it is not mandatory, and very few stations do it. If the hydrostatic test causes a crack it won’t be picked up until the next visual inspection one year later. It’s very rare to find a cylinder that’s leaking through a crack in the neck between the test periods.

Can you tell us the difference between the normal filling rate and the hydrostatic filling rate? What extra pressure does the hydrostatic test put on the cylinder to show up any weakness?

The recommended fill rate put out by Luxfer is between two and four megapascals per minute. The hydrostat fill rate is ten times that rate.

That’s quite a severe test on a cylinder.

It’s very severe.

In your operation it’s crucial that you look at the cylinder after you’ve done the hydro.

Yes, and Luxfer have put this out in one of their bulletins which all test stations in New Zealand received.

Is there any particular cylinder that seems to be having more problems than other cylinders?

In New Zealand there’s really only the one brand of cylinder which has more problems, which is Luxfer. The majority of cracking is in the American-manufactured 80 cubic foot aluminium cylinders, and the Australian CIG manufactured cylinder. We’ve noted that the American cylinders manufactured up to about 1988 seemed to be cracking: E6498, SP6498 or DOT3AL. It’s been extremely rare to get one cracked that’s been manufactured after 1988. We haven’t noticed anything in later cylinders, but you must remember that there are very few of those cylinders imported into New Zealand.

In your opinion, has there been a change in the manufacture of the cylinder, or do you feel that it has something to do with the composition of the aluminium being used?

I couldn’t say. We know that Luxfer changed their manufacturing procedure, and they’ve changed their aluminium alloys.

With the inspection around the neck, I know that some people say that when the extrusion is rounded off at the neck of the cylinder you can see some folds. Are those folds quite common?

It’s very rare to see those folds in the American manufactured cylinders. The Australian CIG manufactured cylinders had a lot of folds in the early years, but most of those have now been taken out of the system and all the new cylinders are very smooth.

What do you feel is the cause of cracking? Is it diver abuse, or do you feel that it’s inherent in the cylinders themselves?

I’d like to comment on the ‘Safety First’ bulletin put out by Luxfer in Australia, in which they imply that it is up to the owner to look after the cylinder and this can prevent problems. In our opinion it would be totally the manufacturer’s problem that cylinders are cracking.

In the 40 years that you’ve been diving, Brian, have you had any of your own cylinders fail?

I had quite a few HOAL2 English Luxfer cylinders and American Luxfer cylinders. All the American Luxfer cylinders that I owned have failed, and the HOAL2 cylinders, which were manufactured in 1976, are still fine.

I understand that when cylinders are designed they have an unlimited life as far as filling is concerned to meet safety standards, but the cylinders don’t seem to be getting anywhere near the life expectancy stated in the manufacturing specifications.

All these cylinders that crack or fail are not up to the manufacturer’s specification. It’s as simple as that.

Do you feel that the testing procedures done by some facilities are not up to scratch?

Yes, we do. We believe that you must have good cleaning facilities, a visual inspection facility with a turntable that’s set at the correct height so that you can turn the cylinder around smoothly. A lot of the cracks cannot be detected unless you have a large oval mirror and a suitable magnification device. You can’t buy it as stock, it has to be made up, or an existing one modified. I went to a large station recently where they rolled the cylinder between two treads of a staircase to do the visual inspection. You cannot possibly do a good job that way.

When a tank arrives at Air Technology, what’s the procedure?

Paperwork’s filled in, valves are removed and it’s inspected. If it’s dirty, and a lot of them are, it has to be cleaned with an acid called Version. This dirtiness comes from the fact that over a period of time a small amount of salt water will go down the valve and get into the cylinder through bad filling procedures. This salt water will corrode the threads, so you cannot see if the cylinder is cracked. We clean it for 24 hours in Version, then water, then isopropyl alcohol, and then inspect it again. We then hydrostat test it, re-inspect it and then dry it. The valve is torqued back in the cylinder, not put in and tightened up with a very large spanner like so many stations do. 1.5% of all the aluminium cylinders we inspect are cracked. During the last recall, at the end of the ‘80s, there was a total of 3,618 tanks inspected. 3,013 passed, which was a 17% failure rate. Failures varied from 45% in some stations to 0% in others, so we know the 45% stations obviously were seeing cracks that weren’t there, and those that had a really low percentage were not picking the cracks up. They are extremely difficult to pick up.

Recently there has been publicity for electronic devices which can be used to detect cracks. What’s your opinion of those?

It’s just another tool that can be useful, but if you’re going to have to clean the threads to use the machine, then you may as well do a visual inspection.

With the risk of cylinders exploding during fills, have you taken any precautions in-house to protect your staff and customers?

We’re fairly relaxed filling cylinders that we’ve tested, but we aren’t so happy filling cylinders that other stations may have tested. We’ve put in a heavy duty water bath and a reinforced concrete-filled block wall so that our staff are protected during the filling procedure.

In the last 12 months how many cylinders have you filled, and how many would you have condemned due to cracking?

We fill just under 12,000 cylinders a year. In the last 12 months we have condemned about 22.

With these cylinders cracking, what would you like the industry and manufacturers to put in place to help prevent a major accident?

One of the problems is that both Telarc and NZU stations are audited, but the auditing really only tests the paperwork and the procedures. There’s no ongoing education of station operators. If you wanted to open a testing station tomorrow, you don’t have to have any qualifications to do that. You are required to have some training, and there are some training procedures that have been set out by NZU; however, the person teaching you doesn’t have to be trained. Any instructor can teach you within several hours the theory behind testing tanks, and he gets that knowledge out of a book.

So at the moment there’s no training programme that people can go along to and have hands-on training?

Well, I can’t speak for the Telarc stations, but I know that the NZU auditor considers that they are qualified to do the tank testing training. So NZU are providing training. When we sell hydrostat test equipment we’ve always trained the operator. We must have them for one day so that when they buy the equipment we’re happy that they can use it.

Are divers have difficulty getting these suspect models tested and filled?

Yes. One of the big problems is when we test the cylinders and we’re happy that they’ve got no cracks when they leave us. But if someone goes out of town for his holidays, he can’t get the cylinder filled, because in some areas everyone says they won’t fill those particular cylinders or test them. So the customer comes back to Auckland and has a row with us because we’ve taken his money and done the tests, but he still can’t get it filled anywhere except by some of the Auckland stations. If there’s not going to be an overall policy, then in our opinion the cylinders should be withdrawn from service. Who pays is entirely a commercial decision, but as far as safety and the way the industry’s going, it will be far better if the cylinders are pulled out of operation.

Do you feel that someone could end up getting killed?

Someone will get killed. I read somewhere that there have been five accidents in Australia over the last few years, fortunately with no injuries. New Zealand has had one in Wellington that blew a garage up, one in Maketu, one at Richmond Sports, and one in Tairua. We’ve had four with one major injury, and three were in one year.

From what I can see, there seems to be an upsurge in people using steel cylinders again. Have you seen a similar problem with steel cylinders?

No. However, NZU have put out a code of practice that says you must crack the valve prior to filling to displace any water that may be in the valve, and to check that the air is not contaminated. This is still not being done, so we’re seeing a lot of steel cylinders after one year of operation coming in with quite bad rusting. But this is a procedural matter at the filling stations. If the cylinder is in a boat and salt spray goes on the cylinder, you can get up to a teaspoon of salt water going into the cylinder valve. So when the cylinder is filled the water gets pushed in. Even though it is well known and a procedural matter, they still don’t do it. A lot of the problems leveled back at the diver/owner are really the testing station’s and the filling station’s fault.

What can divers do to maintain their tanks?

All you can do is wash it down after you’ve used it, make sure you don’t drop it or bang the valve, and ensure that you do not breathe the tank completely empty. There’s not much else you can do. New Zealand seems to have more problems with the older Luxfer cylinders. Very few were imported into Australia, so the problem is not so prominent there. America had a lot, but they only hydro every five years. The difference in New Zealand is that we hydro every two years, and we had a lot of these cylinders. This could be why we have so many cracked cylinders.

So you’re suggesting that hydro testing every two years is detrimental to the life of the tank?

It could be, but we haven’t got any data that says it is.

There have been suggestions that after ten years cylinders should be condemned and the diver would have to purchase a new cylinder. What’s your opinion of that idea?

I’m totally opposed to it. There’s many steel cylinders around that are over 40 years old and are still as good as gold, and there are thousands of HOAL2 UK-manufactured Luxfer cylinders that have never given any problems. In fact, we have never heard of or seen a HOAL2 cylinder with a crack.

In other words, you would agree with the old saying ‘Buy an aluminium cylinder and it should last your diving life.’

I would agree that it should last your diving life.

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