SOME steel tanks. Not all.
Air cylinders
- Thread starter TheHuth
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Skulmoski
Contributor
I stand corrected, I've never seen concave based steels but it appears they do exist
Ahh a technicality. Aluminum corrodes Although to be pedantic they both oxidize and to take geekyness to the extreme Aluminum suffers from 11 different types of corrosion, Steel only 7
As applied to Scuba cylinders
Now ask me about NDT (NDI)
The University of Rode Island has a PDF article on testing AL and AA/ST tanks. It was conducted in the 1970s, but it contains some nice information. I couldn't find the report online so I obtained it through my university library via Inter Library Loan.
Rred
Contributor
Huth-
Your idea of renting some different tanks and comparing them is the best way to go.
I started with an Alu80 because they were all the rage and "so much better"...not to mention way cheaper. Bought a steel 96 as my second tank, and took 9# off my weight belt, and gained some 20% more air, which translates into a much higher safety margin, or a longer dive time, at no extra cost to me as a diver. Note that some steel tanks are a different diameter from aluminum, mixing tanks means readjusting the backstrap and can be a PITA.
But with hp tanks, you have a problem in that many shops barely fill to 3000 psi cold, they won't do hp fills. You'd need to check out the shops you plan to use.
If you look at the tank specs on any major dive shop's site, they will list the buoyancy full and empty. Some of the steel tanks are damn near neutral. Some of the aluminum tanks (like the Alu80) are big CORKS when they are empty, and you'll be lugging around extra weight to compensate for that. Especially if you follow the "newfangled" rule of coming back with 1000# still in the tank. (More new nonsense to some of us old farts.)
If you'll be doing trips & rentals--and when you add in the cost of the VIPs and hydros and fills, rentals are NOT such a bad deal in many places--you may want to stick with Alu80's just because they are "standard". Personally? That's like buying tube sox because "one size fits all".
Your idea of renting some different tanks and comparing them is the best way to go.
I started with an Alu80 because they were all the rage and "so much better"...not to mention way cheaper. Bought a steel 96 as my second tank, and took 9# off my weight belt, and gained some 20% more air, which translates into a much higher safety margin, or a longer dive time, at no extra cost to me as a diver. Note that some steel tanks are a different diameter from aluminum, mixing tanks means readjusting the backstrap and can be a PITA.
But with hp tanks, you have a problem in that many shops barely fill to 3000 psi cold, they won't do hp fills. You'd need to check out the shops you plan to use.
If you look at the tank specs on any major dive shop's site, they will list the buoyancy full and empty. Some of the steel tanks are damn near neutral. Some of the aluminum tanks (like the Alu80) are big CORKS when they are empty, and you'll be lugging around extra weight to compensate for that. Especially if you follow the "newfangled" rule of coming back with 1000# still in the tank. (More new nonsense to some of us old farts.)
If you'll be doing trips & rentals--and when you add in the cost of the VIPs and hydros and fills, rentals are NOT such a bad deal in many places--you may want to stick with Alu80's just because they are "standard". Personally? That's like buying tube sox because "one size fits all".
OP
TheHuth
Contributor
I just bought a pair of Steel tanks off Craigslist. I only paid $50, so I figured it was a good deal. I'm guessing they both need a hydro inspection. How do I read the print at the top of the cylinder? I know it indicates brand, and size, and such.
They both look good. Of course only the hydro will say for sure. In any event, I'm not in for allot of money, so if they both end up bad, it wont be a huge loss.
They both look good. Of course only the hydro will say for sure. In any event, I'm not in for allot of money, so if they both end up bad, it wont be a huge loss.
I never said anything about corrosion, I said rust. I'm still looking to find rust on an aluminium tank.Ahh a technicality. Aluminum corrodes Although to be pedantic they both oxidize and to take geekyness to the extreme Aluminum suffers from 11 different types of corrosion, Steel only 7
And I'm pretty damn sure if you leave an aluminium and a steel tank in salt water for a while, the aluminium will be looking much better than the steel one
.Some of us like those, because we'd be pretty much overweighted with any steel tank
RUST IS CORROSION!!
Both Aluminum and Steel corrode through oxidisation. They just go different colours!
Steel tanks are protected by a galvanic coating, Ali tanks by an Anodic coating
If you put either material unprotected in sea water, then they will be eaten through like a hot knife through butter.
Trust me on this, I had over10 years as an aerospace materials scientist and have had input on most passenger aircraft in service, so you'd better hope I know my stuff
Each material has its benefits and its disadvantages. You pick the cylinder material to suit your needs and budget. Although Ali gets heavier than steel and just as negative if not more so once you get past 12l tanks. But nothing wrong with Al 80s if you like their buoyancy characteristics
CuzzA
Wetwork for Hire
It's only a good deal if they pass hydro. At least with aluminum you can get a few bucks back on scrap... Steel, not so much.
Post a picture of the stamped digits around the top of the tank or post what they are. Also post the hydro dates. Do the tanks have a vip sticker? What's that date? Are they full of air or are they empty?
Rred
Contributor
The hydro dates will seach be stamped next to the "hallmark" of the hydro facility, often a triangular cluster of numbers. The hydro will show numbers over 1/4", fairly obvious once you see them, in a sequence like 8 H 05, where 8-05 is the date (only 2 digits for the year) and the H in th emiddle is where the hallmark will be. (Could be 1974 and still good.) They're usually stamped all higgledy-piggeldy around the neck and shoulder. The hallmark is often something like a triangle with numbers in it, not just a simple letter, and that's the easy way to spot the hydro stamp.
Some extinguisher shops that do hydro testing will charge $25 per tank. Some dive shops will charge $25, others $45, and another $20 for a VIP of each tank on top of that. Which may or may not include a new o-ring for the tank.
A lot of shops tend to get insulted and find other ways to add charges, if you haven't had them do the whole process. Which often manages to take a week or two.
If the tank has any rust or corrosion inside it, they'll probably tell you that it needs to be tumbled, add another $20-25 per tank. There's no reason why you can't bleed the tanks dry, open them up, and drop in an LED string to take a look around yourself, before investing in all that. If the tanks were properly maintained, they could be just fine.
Some extinguisher shops that do hydro testing will charge $25 per tank. Some dive shops will charge $25, others $45, and another $20 for a VIP of each tank on top of that. Which may or may not include a new o-ring for the tank.
A lot of shops tend to get insulted and find other ways to add charges, if you haven't had them do the whole process. Which often manages to take a week or two.
If the tank has any rust or corrosion inside it, they'll probably tell you that it needs to be tumbled, add another $20-25 per tank. There's no reason why you can't bleed the tanks dry, open them up, and drop in an LED string to take a look around yourself, before investing in all that. If the tanks were properly maintained, they could be just fine.
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