Scuba Tanks Steel 72

[JLambus]

I thought this craigs list add was funny and thought the vintage divers coulds appreciate it.



Scuba Tanks Steel 72 for sale. Be cool buy one. - $75 (Kona)

Date: 2011-07-28, 1:24PM HST
Reply to: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I am selling a bunch of steel 72cu ft tanks. They all have 08 hydros and current viz stickers. They will all pass hydro again, because they are steel.
Why steel? Steel tanks are better than aluminum tanks... dont think so? Here's why...

Steels are lighter, about 3 lbs lighter. Whiny diver says: "But they feel heavier", that's because they are denser. And because of that they ARE heavier underwater. Now you've taken weight off your back, and weight off your belt. usually around 4lbs less lead, meaning about 7lbs total. They have more air. Whiny Diver says: "but they have less pressure" true but pressure does not denote your volume. Your volume denotes your volume. An aluminum 72 filled to 3000psi is the EXACT same VOLUME of air as a steel 72 filled to 2250. WD:"My aluminum eighty has more air in it" Does it? Catalina 80's don't actually have 80 cubic feet of air in them. WD: " Why do they call them that then? " Because they are giving you an over pressure rating to 3300 psi. Your tank at 3000 psi is more like 77cu ft. Does your dive shop overfill your tanks? cause if not then You don't have an 80, you have a 77. And if they do well let's look at the math for a steel 72. Over pressure rated that same 10% you'd get an additional 225psi in your tank, putting you at a 2475psi fill. At that pressure your steel 72 now becomes a 79.2. Less than 1 cubic foot from an 80. And because of your new found density and the smaller change in pressure you wont be bobbing up to the surface at the end of your dive anymore, Saving you energy from kicking down the last half of your dive. They are smaller on the outside of the tank, which will make you more streamline and improve your air consumption. Which also means you exert less energy giving you the edge to out breathe your buddies and to not get decompression sickness. WD: "But my local dive shop always gives me back my steels with only 1900psi in them." Well that because they're stupid. Ok, lets be fair...... maybe they have a broken pressure gauge, or..... no, never mind, they are just stupid. Sorry to be the one to have to tell you this. I know they have pretty pictures on their walls, I know the little blonde counter girl is cute, but why not take your tanks to somewhere like KDC or BID where you'll get proper fills (they have cute girls and pretty pictures too). Tim over at SID is a big fan of steels and while he's not a cute girl, he is a federal government certified hydro facility operator. Or hey keep taking it to your normal dive shop, maybe one day you'll get it back with 3200psi in it like I did once when forced to take it there. WD: "Don't they explode because they are older." No this is a common misconception that happened cause people were filling improperly maintained steels that have rusted over the years, the same would happen to an aluminum that had been poorly cared for with lots of pitting and corrosion. In fact the only tanks made for scuba that ever have exploded due to manufacture defects, have been aluminums, made with a bad alloy that causes sustained load cracking, a phenomena that has never ever been observed in a steel tank ever...... ever. In fact the only tanks that LOOKED good that I sent to hydro and failed were aluminums. And I have sent hundreds of tanks to hydro. Steels always pass. Well mine always have. My aluminums have not. WD: "well why do all the dive shops use aluminum tanks then?" Because aluminum is cheaper. A new aluminum tank costs about $180, a new steel tank costs about $280, when you are opening a dive shop and buying 100 tanks to get started you'll save 10,000 big ones if you go aluminum. Geez you whiny divers ask a lot of questions. Just believe me and buy my tanks. I'm broke. Let's recap.

They are lighter above water. (weight off your back)
They are Heavier underwater. (weight off your belt)
Same amount of air.
Better buoyancy characteristics.
Helps you streamline your rig.
Fit more tanks in your car/ Takes up less storage space.
Stronger material, more likely to pass hydro if cared for properly.
Better quality tank at a less than half the price.
Maybe you'll find a new dive shop you like more. (cuter girls)
Out breathe your friends. (and if they think its on a smaller tank then all the better)
Less chance of DCS (Might just save your life) ....... ;-)
You'll get to meet me.
You might get to own a scuba tank that Jerry Garcia once used.
You'll look cooler, and get to laugh at Allys (that's what us hipster steel tank divers call aluminum tank divers)


Call xxxxx 808-xxx-xxxx
Ladies: sorry I'm no longer single. Don't wait so long next time.

 

[JamesBon92007]

I didn't know I could hold my breath that long. I don't see where it says how much he's selling them for.

 

[DrunkenParrot]

Haha I love craigs list ads

 

[AfterDark]

I didn't know I could hold my breath that long. I don't see where it says how much he's selling them for.

Some 007 you are right at the top: Scuba Tanks Steel 72 for sale. Be cool buy one. - $75 (Kona)

 

[duckbill]

Entertaining ad. Thanks for sharing that.

However, he's wrong on at least one point...

Over pressure rated that same 10% you'd get an additional 225psi in your tank, putting you at a 2475psi fill. At that pressure your steel 72 now becomes a 79.2

A steel 72 is actually 71.2 cubic feet, and that is at the 10%, 2475psi overfill.

 

[JamesBon92007]

I've also never heard that an aluminum 80 is not 80 cu/ft at 3000 psi. I thought it didn't need the +10% to achieve what it's rating is. I do know that an aluminum 80 filled to 3000 psi lasts longer than a steel 72 filled to 2475 because I have used both many times

I'm also skeptical about the "In fact the only tanks made for scuba that ever have exploded due to manufacture defects, have been aluminums" I have seen at least one steel 72 that ruptured violently but I suppose it could be blamed on neglect.

Oh dear, I missed the price right at the top! And that's the first mistake I've EVER made Aside from all that, one of the reasons James Bond was so popular was because he was human and fallable, but always prevailed anyway!

 

[DA Aquamaster]

Aluminum 80s are in fact only 77s. And as noted above a steel 72 is 71.2 cu ft at 2,475 psi, and only 64.7 cu ft at 2,250 psi.

But to be fair, the average shop filled AL 80 is only filled to about 2800 psi after it cools to room temp ant at that pressure it only holds 71.8 cu ft. So a plus filled steel tank is essentially equal to a hot filled AL 80. Consequently any real differences depend on fill practices.

3A (carbon steel) and 3AA (chrome moly steel) steel tanks are the only tanks that are plus rated. That practice started with welding tanks during WWII due to a shortage of welding tanks and continued as a permanent practice after the war. Most steel tanks will continue to qualify for a plus rating but not all hydro test facilities will do it for scuba tanks and having it done requires the REE number for the tank - and not all test facilities have proper documentation for that for all tanks.

3AL aluminum tanks have never been approved for a plus rating and never will be due to the properties of the metal.

Pitting and line corrosion are the two big killers of steel tanks and the main reasons for both failure and for condemnation. It's almost unheard of for a properly manufactured and non abused steel tank to fail requalification due to failing the hydro portion if the test - if the test is properly performed.

 

[JamesBon92007]

I think most of us old farts know that a "72" is really just 71.2, but this is the first time I've heard that an aluminum 80 is only 77. Was this a well-kept secret of some sort? Or was it that I quit my subscription to Skin Diver Magazine about the time I got my first aluminum 80?

 

[Luis H]

The way these pressure cylinders are made they tend to vary in dimensions.

I have not actually measured an aluminum 80 cylinder, but they are known to be about 77 cu ft at 3000. I am just not that interested on AL 80 (I only own two), but I have one that needs a hydro so I will measure the actual volume when I fill it with water.

I have precisely measured 9 of my steel 72 (so far) and the average volume of these 9 is 70.8 cu ft.

Here is the measure volume of the 9 tanks, the manufacturer, and year of manufacture:
72.2 Norris 1968
70.5 PST 1962
69.6 Norris 1975
70.8 PST 1960
71.4 Norris 1970
70.9 PST 1976
70.3 Norris 1974
71.4 Norris 1962
70.2 PST 1960

The PST seems to be more consistent with an average volume of 70.6 cu ft.

The Norris averaged 71.0 cu ft; they ranged from 69.6 to 72.2 cu ft.

Added:
It makes scene we call them steel 72 since you could loosely round them up to 72. But assuming that they are 71.2 is a bit miss-leading since using three significant digits for something that varies so much is not accurate. I would say they average about 71 cu ft.

This is just an engineering technicality, but it does bother me to imply that something is more precise than it is. Since the invention of the electronic calculator we now see bunches of digits after the decimal point on items that are just not that precise.



The volume was measure by precisely measuring the weight of the water capacity.


The most surprising finding among all my tank measurements is that my wife’s two PST hp 80 actually hold 85.3 and 85.0 cu-ft at 3442 psi. I would have thought that they would always advertise at least the measure capacity or a rounded up number.

 

[duckbill]

I have precisely measured 9 of my steel 72 (so far) and the average volume of these 9 is 70.8 cu ft.

Calculated for 2475 psi?