Anybody hear of exploding tanks lately?

[Web Monkey]

On my last trip to Cozumel, I noticed that the AL 80's on the boat had apparently never been hydroed or VIP'd and were really old.

They also had close to 4000 PSI in a 3000 PSI tank.

Since we were already in the boat heading out to the dive site, and they hadn't blown up in the last several thousand dives, I figured the chances of them exploding right then were slim, and did my part to reduce the tank pressure by diving with it.

Anybody hear of any of these little gems exploding?

Terry

 

[Drew Sailbum]

thankfully rarely, and you don't want to be around when it happens. Not testing cylinders in heavy resort rotation is nothing short of foolish IMHO.

I am in the midst of doing the annual visual inspections at our shop. I have already condemned one cylinder which passed hydro in the fall of 2002. I don't think it would have lasted until the next required hydro in 2007.

At our shop all cylinders are subjected to a 5 year hydro cycle and a 1 year visual inspection cycle. All of our cylinders are 6061 aluminum alloy.

If the old cylinders you saw were of the 6351 alloy, then lack of routine testing would be outright reckless. This alloy is known for having a problem with sustained load cracking which would only be compounded by routinely overfilling. I would subject such cylinders to a much shorter inspection cycle if they are in heavy rotation in a resort environment. Perhaps a 6 month Visual with Eddy Current testing and a 2 year hydro cycle.

 

[scubafanatic]

Hi Web Monkey,

...quick question......which dive operator did you use? I ask because I've been to Coz twice and both times I was lucky to get tanks just filled to their rated pressure......usually they were underfilled by something like 300 psi...and this was true for both the AL80's and the LP 95's I used.

I'd like to hook up with an operator that's 'generous' with their air fills........although I'll admit 4000 psi in an AL80 is overdoing it a bit.

Karl

 

[Web Monkey]

It was a couple of years ago and I'd need to find a map of Cozumel to dig them up. I was actually looking for someone else, and the taxi dropped me off at the wrong shop and took off, so I figured i'd give them a try.

Terry

Hi Web Monkey,
...quick question......which dive operator did you use? I ask because I've been to Coz twice and both times I was lucky to get tanks just filled to their rated pressure......usually they were underfilled by something like 300 psi...and this was true for both the AL80's and the LP 95's I used.
Karl

 

[Mako Mark]

Lack of testing in not just confined to the resort areas, but it is more common there. I find that many operators just dont have access to good tesiting facilities.

I know that testing facilities are becoming more common in the cancun, Cozumel region, but there are many shops that use a tank untill the neck leaks intolerably, then they sell them to local fishermen. It is nearly as cheap to buy a new tank as to get an old one tested in some places.

Sad but true. the moral is keep a sharp eye out for this when you are in remote locations.

 

[archman]

Maybe they were just hot? REAL HOT!

 

[FredT]

Several areas do not even have a requirement for hydros OR visuals. Just as most of the world does not require burst disks, many areas don't do hydros. The "rules" vary a lot.

The Bahamas did not require hydros or visuals when I lived there a few years ago. Strangely enough there were also no facilities to get them done in country. To get tanks hydroed we had to ship them to the states, have them hydroed, then ship them home again. Had I not been in a "duty free" zone we would also have had to pay import duties on them again. In the year and half I was there I inspected over 200 tanks that had hydros up to 25 years old. Roughly a third of the aluminum tanks failed visual before hydro due to problems with the valve seat or excessive pitting. I did arrange a "deal" for hydros in Vero Beach when I had a ship scheduled to make the crossing that also had available deck space for the cargo container. Shipping by mail or commercial carrier would have been over $70 per tank. I think the hydro shop driver was a bit surprised to find a conex container full of valveless tanks to do all at once. We did get a good price on the lot, and he finished inside the allowed time window. If I remember correctly only about 10 of them, mostly badly abused 1/2" valved steels, failed the hydro.

FT

 

[zboss]

It was a couple of years ago and I'd need to find a map of Cozumel to dig them up. I was actually looking for someone else, and the taxi dropped me off at the wrong shop and took off, so I figured i'd give them a try.

Terry

He dropped you off at the right place...

 

[pescador775]

BOOM
A steel tank which is in good shape externally and internally is not going to explode when filled to nominal pressures, even if not hydro tested in many years. Rusty tanks can and do explode. This seems to happen in third world countries without much notice by the public.

An aluminum tank of the 6351 alloy should be inspected regularly. There were some bad alloy runs in a 2-3 year period. Kidde tanks from 81-83 are especially suspect. There have been problems with other years but these haven't figured in as many well publicised explosions. Tanks which have been heated can explode regardless of Al alloy.

I believe and will continue to assert that hydro tests of Al tanks are responsible for the initial tiny cracks which propagate into neck failures under the so called 'sustained load' theory. However, I believe that shock loading, not 'sustained', small loads, are responsible for the initiation. It is not surprising that recently tested tanks fail inspection a year later. Therefore, I would expect that Al tanks of 6351 alloy which have been inspected, but not tested, would be relatively safe to use at nominal rated pressure.

Steel tanks seem to fail hydro for no apparent reason. I believe that manufacturers are responsible and contribute to the problem because of lapses in quality control.

 

[Tavi]

I know of one operator in the Bahamas who inspects his tanks regularly and keeps records. With the tanks belonging to him and being used at his business only, putting stickers on them would be an unecessary expense.