PCDC Storage bottle blows

[jviehe]

Of course, these tanks are sitting outside in salt air 24/7. That cant be good.

 

[Leadking]

Those 2 photos don't show anything obvious. The seam split adjacent to the weld at the edge of the heat effected zone, just like it's supposed to. The end cap appears to have a weld metal failure, but to determine if this was a primary or secondary failure will take a lot more investigation. That will take a few days of stereo microscope work at least to nail down the exact crack initiation point(s), then it starts to get interesting.

I am not saying the construction had anything to do with failure, just that compared to scuba cylinders, they're interesting.

 

[FredT]

Agreed. Be aware that there are DOT specs for welded pressure vessels too, as well as the ASME specs. If I remember correctly the diesel submarine bottles were seamless with hot spun ends.

The photos do prove however that they were NOT the known problematic torpedo bottles.

 

[TheMadDane]

Is it just my metallurgical ignorance or does that bottle look pitted and corroded on the inside?

 

[DA Aquamaster]

Is it just my metallurgical ignorance or does that bottle look pitted and corroded on the inside?

There are pretty impressive pits caused by corrosion. Of course at what point a pit becomes a reason to fail the tank depends on the tank and the specifications set forth by the manufacturer. If the tank is over engineered and has a lot more wall thickness than it needs, a larger pit can be tolerated.

Scuba tanks are designed to be easily portable and that portability creates a design constraint for the wall thickness and total weight of the tank. That is not as much of an issue for a tank that is not intended to be portable and where weight is not as significant a factor. In that case, if a 1/4" wall thickness is required, you could have 1/2" walls and a tank that weighs twice as much and not really have a problem. In the latter case, a pit could be larger and deeper before it begins to create a stress riser that is significant from a safety perspective.

But with the tank in question the corrosion and pitting visible in the picture is so expansive that it would have made me nervous.

 

[CompuDude]

True about tumbling, it is not cost effective. We have used a whip once. The key is preventing as much moisture from entering as possible. Testing often, and crying when you have to take them out of service...

There are pretty impressive pits caused by corrosion. Of course at what point a pit becomes a reason to fail the tank depends on the tank and the specifications set forth by the manufacturer. If the tank is over engineered and has a lot more wall thickness than it needs, a larger pit can be tolerated.

Scuba tanks are designed to be easily portable and that portability creates a design constraint for the wall thickness and total weight of the tank. That is not as much of an issue for a tank that is not intended to be portable and where weight is not as significant a factor. In that case, if a 1/4" wall thickness is required, you could have 1/2" walls and a tank that weighs twice as much and not really have a problem. In the latter case, a pit could be larger and deeper before it begins to create a stress riser that is significant from a safety perspective.

But with the tank in question the corrosion and pitting visible in the picture is so expansive that it would have made me nervous.

I had the same thought when I looked at the photos (posted on another forum). Those look to be some pretty MAJOR pits and corrosion. Maybe they're not the reason for the failure, maybe they are, but from the standpoint of my PSI training, there's no way in heck that tank would have passed any sort of visual inspection.

Scuba-grade air from properly-maintained compressor filtration stacks should be bone dry, right? Looks like a fairly large amount of moisture has been getting inside that bottle to cause that much corrosion.

I'm curious about the opinion of others with more experience on the subject.

 

[DA Aquamaster]

The picture also shows only a limited area of the tank - I'd love to see the pitting in areas near where the failure started.

 

[PhilEllis]

Also, there should be no such thing as non revenue fills. The cost of fills for classes, instructors and dive masters should be taken into account in the cost of the per student classes.

Oh, that is worth a thread all by itself!

Phil Ellis
www.divesports.com

 

[Rick Murchison]

Oh, that is worth a thread all by itself!

Phil Ellis
www.divesports.com

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A ScubaBoard Staff Message...

So shall ye ask, so shall it be done...
Discussion on the profitability of fill stations moved here.
Rick

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[Doc Harry]

2) A hammer test consists of tapping a cylinder a light blow with a suitably sized hammer. A cylinder emptied of liquid content, with a clean internal surface, standing free, will have a clear ring. Cylinders with internal corrosion with give a duller ring dependent upon the amount of corrosion and accumulation of foreign material. Such cylinders shall be investigated. The hammer test is very sensitive and is an easy, quick, and convenient test that can be made without removing the valve before each charging. It is an invaluable indicator of internal corrosion.

BTW, hammer test applies only to steel cylinders