Equipment Dive School Fined For Negligence - Australia

[Kay Dee]

I know zero about tank testing and inspection procedures, so can someone who has done this explain how it’s done, what they look for, and what criteria would have been used to inspect this tank and rejected it? How would the defect in this tank have likely been detected during the inspection and testing process to re-certify it?

Its been a long while since I was involved in hydro testing any cylinders in Oz, but if my memory serves me well, which it sometimes doesn't, it went something like this, or thereabouts anyway.

The cylinder was first emptied (and the valve removed) and inspected both externally and internally by the Mk1 eyeball for any damage or corrosion, and other test failure criteria as per Aust. Standards. (The internal one was done using a long handle ‘dental’ type mirror and narrow light-stick/wand, or if you were ‘up-market’ a video snake-eye with built in ring-light.) If all good the cylinder was then filled with water and pressurised to, IIRC, (and there is no guarantee I do ) 1.5 time above its WP (working pressure) to its TP (test pressure), e.g. 3000psi WP to 4500psi TP / 200bar WP to 300bar TP (or was it 350bar?). The tank was then left pressurised as such while still connected by the fill hose to the test gauge (highly accurate Aust. Standards certified pressure gauge no less) and sits pressurised for the prescribed amount of time (yeah sure, you really think I remember that detail). Then, as long as there is no variation (or maybe a stated bare minimum, I cant recall your honour) it is considered to have passed the test. It was then manually stamped as such including test date somewhere at the top of the cylinder near the neck and wallah (no, not allah) your good to go for another year. Oh, and of course, if it was an oxygen clean cylinder to start with you then needed to o2 clean it again. And if you had a couple of dozen nitrox cylinders as I did in those daze, all fun and joy, every damn year, it wasn't!

And, again of course, the person doing the testing, and the facility where the test was taking place, had to be a certified hydro tester / testing station.

 

[clownfishsydney]

Do we know what kind of tank? LP to 3000 or 3500? Cave fill? It would help to know all the extenuating circumstances and not Just NO VIS/HYD = BAD. Of course we need HYD and VIS. Just wondering if any other facts were omitted?

Virtually all tanks in Australia are 232 bar (say 3365 psi). The only exceptions would be very old aluminium ones which basically all dive shops have banned. Most tanks are filled only to 210 or 22 bar, very few fill to 230. There is no such thing as a cave fill in Australia as we have higher pressure tanks in the first place. As I pointed out above, we have to have a hydro EVERY year.

 

[Seepferdchencam]

The story goes that this tank had a boot without drainage holes and the bottom of the tank was severely corroded leading to failure. As to the facts, I can't say.

 

[elmo]

Virtually all tanks in Australia are 232 bar (say 3365 psi). The only exceptions would be very old aluminium ones which basically all dive shops have banned. Most tanks are filled only to 210 or 22 bar, very few fill to 230. There is no such thing as a cave fill in Australia as we have higher pressure tanks in the first place. As I pointed out above, we have to have a hydro EVERY year.

My experience (mostly around Melbourne and Mt Gambier) is a little different. Definitely 232 bar steels are most common, but plenty of 207 bar (3000 psi) aluminium stage/deco/pony cylinders around. Most fills I receive are to (or close to) rated pressures when cool. Agree cave fills are not a thing I’ve come across, and I’ve never seen one of the old aluminium alloy cylinders, except cut in half on display.

 

[elmo]

The story goes that this tank had a boot without drainage holes and the bottom of the tank was severely corroded leading to failure. As to the facts, I can't say.

If that’s the case I wonder if an annual visual inspection, even without hydro, would have caught this case before it happened.

 

[Seepferdchencam]

If that’s the case I wonder if an annual visual inspection, even without hydro, would have caught this case before it happened.

You'd have to assume so, provided they took the boot off for a squizz.

 

[Kay Dee]

My experience (mostly around Melbourne and Mt Gambier) is a little different. Definitely 232 bar steels are most common, but plenty of 207 bar (3000 psi) aluminium stage/deco/pony cylinders around. Most fills I receive are to (or close to) rated pressures when cool. Agree cave fills are not a thing I’ve come across, and I’ve never seen one of the old aluminium alloy cylinders, except cut in half on display.

What a difference a decade makes if steel is now the predominate cylinder Down Under.

When I last had anything to do with (see above) a hydro facility Down Under ally cylinders would have still made up 90% or more of the total that came through for testing, or fills. The ‘recreational’ dive industry seemed to shun steels like the plague for many years, with dive shops own rental stocks being all, or almost all, ally in most places (unless the shop had something to do with the ‘tech’ or cave side of things).

Granted, the area I lived in, and the overall area where the cylinders came from to be tested at the facility I was involved with, was predominately a ‘recreational’ depth (i.e. with this phrase I mean shallow) diving area*. It was only as ‘tech’ became more popular, (well ‘popular’ would hardly be the right word for back then, but at least more accepted) in the late 90’s / early 2000’s that steels began to infiltrate somewhat, and only somewhat. 'Recreationlly' though it was still all ally even as late as 2010 or so. Of course YMMV, but that was the case where I lived (northern NSW, southern Qld) then.

My own stash on the other hand, of about the 30 odd cylinders (which included both my personal ones and those for my business) were predominately 232 bar steels from the get go (plus a couple each of 300bar steels, composites and inconels eventually). And while we did not overfill the 300’s, I cant say the same for the 232’s.

*I imagine hydro stations in Sydney and Melbourne would have seen a greater amount of steels though, as that’s where the larger percentage of divers live/d and where deeper dives were / are conducted more regularly.

 

[Kay Dee]

You'd have to assume so, provided they took the boot off for a squizz.

Any hydro station that did not remove the boot when testing should be drawn and quartered, and would have been by WH&S if caught not doing so!

 

[Seepferdchencam]

Any hydro station that did not remove the boot when testing should be drawn and quartered, and would have been by WH&S if caught not doing so!

Yep.

 

[OMyMyOHellYes]

A hydro test is required every five years subjecting the tank to tremendous pressure to ensure that it'll stand the strain ok.

Kind of. Sort of. At a very basic simplified level. But maybe not really, depending on how that's read.

True that the typical hydro involves over pressurizing the tank with incompressible water to 5/3 of its standard working pressure (at least most in the US, can't speak to AUS standards). They do this, not primarily to see if the tank pops/ruptures, but to measure the expansion of the tank (within defined tolerance) while it is pressurized and then the extent to which it will return to normal volume/displacement after pressure is released.

This process measures the integrity and elasticity of the material and thus its brittleness and/or degree of metal fatigue.