Scrapped an Alum 80 6351 tank today

[DA Aquamaster]

.

/....Aluminum cylinders in any sort of daily service do not last indefinitely and are typically removed from service after 10-15 years because the cost of reconditioning exceeds the cost of scrapping and replacing, with tax consequences also playing a role.

Let's talk about this as well as this is the basis for some shops feeling that any tank over 20 years old should be replaced. That was the story in 2010, yet I don't see shops now saying "no fills for tanks made prior to 1997".

Luxfer has always tested it's aluminum tanks to test pressure for 10,000 cycles. For an AL 80 that's the 5000 psi test pressure, not the 3000 psi service pressure, and the increased pressure will result in increased stress and increased fatigue in aluminum - and it's the fatigue life that is the concern in your statement above.

But how long does it take to get 10,000 cycles?

Assuming a dive shop filled an Al 80 twice a day, seven days a week, 365 days per year, it would take 13.7 years to reach 10,000 cycles. But....10,000 cycles isn't the upper limit even at 5000 psi, and the limit at 3000 psi will be a lot higher as the stress and fatigue is less.

And in practice, how many shops actually fill each of their tanks twice a day, every day? Once a day averaged over an entire year is pushing it, even at a dive resort and at 1x per day you're now looking at 27.4 years to reach 10,000 cycles, which is again a very conservative number when we're talking about 3000 psi service pressure rather than the 5000 psi test pressure.

In our local shop, two fills per week is probably above average and at that rate it'll take 96 years to reach 10,000 cycles. I'm not going to lose any sleep over the old tanks in the rack.

The real killer of aluminum tanks is salt water contamination and corrosion inside the tank followed by abuse of the tank resulting in surface defects deeper than the allowable limits that condemn the tank, followed by fire, which should be cause to condemn any tank.

 

[2airishuman]

::shrug:: You believe what you want. Here's the way I see it.

1) The best available data showed that cracks are missed 3% of the time in a controlled study with a relatively small number of cylinders.
2) Policy in 1994 was based on the incidence of SLC in 1994, and provided a then-reasonable tradeoff of safety vs. cost based on conjecture and limited field experience that showed that a 5-year inspection interval was workable.
3) SLC is cumulative and despite the shrinking population of 6391 cylinders, the number of cracks found continues to grow.
4) While it is true that there have been no ruptures of cylinders due to SLC, in the United States, since inspection began, there have been lesser failures here, such as leaks, and there have been ruptures internationally in countries (Australia) that have largely similar inspection protocols

And so the way the world works, this will continue until a couple of 6391 cylinders rupture and somebody dies, and then PHMSA will require the few remaining ones to be removed from service.

 

[2airishuman]

Let's talk about this as well as this is the basis for some shops feeling that any tank over 20 years old should be replaced. That was the story in 2010, yet I don't see shops now saying "no fills for tanks made prior to 1997".

That isn't what I meant. The point I was trying to make is that dive shops replace their own cylinders within a 10-15 year interval, because of corrosion, or because the paint is flaking off, or whatever.

Luxfer has always tested it's aluminum tanks to test pressure for 10,000 cycles. For an AL 80 that's the 5000 psi test pressure, not the 3000 psi service pressure, and the increased pressure will result in increased stress and increased fatigue in aluminum - and it's the fatigue life that is the concern in your statement above.

No, my point is that typical aluminum cylinders are retired for other reasons if they are in daily service for 10-15 years. Again, corrosion, chipped paint, surface damage whether beyond the official limits or not, or the need for something to expense for tax reasons. Most businesses (LDSs, medical gas places, soda fountain places) as a matter of sound management try to replace their assets on a rotating basis before they actually fail, and I would imagine that a fair number of cylinders get scrapped for that reason. These places all buy cylinders by the pallet, and in the industry as a whole, most aluminum cylinders are smaller and therefore cheaper than the AL80s we use for SCUBA. I don't know exactly what the prices are but when a medical gas outfit has a choice between a new E cylinder for $40 and hydro and repainting for $25 it doesn't take much to tip the decision in favor of the new cylinder.

 

[DA Aquamaster]

That isn't what I meant. The point I was trying to make is that dive shops replace their own cylinders within a 10-15 year interval, because of corrosion, or because the paint is flaking off, or whatever.



No, my point is that typical aluminum cylinders are retired for other reasons if they are in daily service for 10-15 years. Again, corrosion, chipped paint, surface damage whether beyond the official limits or not, or the need for something to expense for tax reasons. Most businesses (LDSs, medical gas places, soda fountain places) as a matter of sound management try to replace their assets on a rotating basis before they actually fail, and I would imagine that a fair number of cylinders get scrapped for that reason. These places all buy cylinders by the pallet, and in the industry as a whole, most aluminum cylinders are smaller and therefore cheaper than the AL80s we use for SCUBA. I don't know exactly what the prices are but when a medical gas outfit has a choice between a new E cylinder for $40 and hydro and repainting for $25 it doesn't take much to tip the decision in favor of the new cylinder.

If a Medical O2 supplier is doing business with a RIN, their hydro costs are probably around $10. Hydro test facilities make their money on volume with medical O2 and CO2 cylinders for the beverage industry. Scuba cylinders are a sideline.

And, smart dive shops just buy brushed aluminum finished cylinders to avoid the whole paint flaking and salt water trapped under the paint issues.

The last time I was in Bermuda, we rented tanks from a little shop on Elbow Beach. They were mostly aluminum tanks dating from the late 1970s. That was 5 years ago and I have no doubt those same bare aluminum tanks are still in daily use there today.

 

[JamesBon92007]

I
And, smart dive shops just buy brushed aluminum finished cylinders to avoid the whole paint flaking and salt water trapped under the paint issues.
.

That may well be however every single dive boat I've been on had blue aluminum 80s. I have not been to Bermuda yet.

I was under the impression that Basic Blue was cheaper to buy initially.

 

[teknitroxdiver]

That may well be however every single dive boat I've been on had blue aluminum 80s. I have not been to Bermuda yet.

I was under the impression that Basic Blue was cheaper to buy initially.

I don't think I've ever been on a boat with any significant number of colored tanks. Have you done all your diving on one boat or with one company? (Perhaps one with a company theme of blue?)

 

[JamesBon92007]

I don't think I've ever been on a boat with any significant number of colored tanks. Have you done all your diving on one boat or with one company? (Perhaps one with a company theme of blue?)

Actually it is because I wear blue-tinted sunglasses. I went back and looked at some pictures from my trips to various places on different dive boats and most of the tanks were silver (brushed aluminum). Early-on all the aluminum 80s I used were light/medium blue and I guess it just stuck in my mind that aluminum 80s are blue. I generally avoid making broad, unfounded statements that I can't back up with facts.

Is it too late to retract my statement? Is there a "delete" button?

 

[DA Aquamaster]

I wouldn't lose any sleep over it.

I really do despise painted aluminum tanks. Some of them are very pretty, but they are a lot harder to maintain, particularly in shop rental.

I'm ambivalent about the tank wraps that are sold now. They are probably ok as long as they are intact, but once they start getting nicked full of holes, they need to come off to prevent water trapping and corrosion and to allow a proper VIP. It doesn't make customers real happy.

 

[Couv]

Is it too late to retract my statement? Is there a "delete" button?

Try these glasses instead.