Fe or Al tank for EANx diving

[sotgecho]

Maybe I am not putting in the correct search query to find out the answer to this question but I am posting this to get people's opinion about tanks.

I am in the market for my first tanks with my recent completion of nitrox certification. I am trying to find out which is more suitable for nitrox diving?

I understand from my training that there are certain considerations when purchasing, filling and maintaining tanks when filled nitrox is steel or aluminum better for these considerations. I know that some steel tanks are ready for use with nitrox right out of the box like XS Scuba tanks but are aluminum tanks ready as well?

What are the advantages/disadvantages of each when using them with nitrox? Or I am asking a no brainer question and just get steel tanks for nitrox and forget considering aluminum at all and just use them for air?

Thanks in advance!

 

[Melicertes]

Maybe I am not putting in the correct search query to find out the answer to this question but I am posting this to get people's opinion about tanks.

I am in the market for my first tanks with my recent completion of nitrox certification. I am trying to find out which is more suitable for nitrox diving?

I understand from my training that there are certain considerations when purchasing, filling and maintaining tanks when filled nitrox is steel or aluminum better for these considerations. I know that some steel tanks are ready for use with nitrox right out of the box like XS Scuba tanks but are aluminum tanks ready as well?

What are the advantages/disadvantages of each when using them with nitrox? Or I am asking a no brainer question and just get steel tanks for nitrox and forget considering aluminum at all and just use them for air?

Thanks in advance!

To my knowledge there is no realistic preference for either above the other if your criteria is to fill them with nitrox. [edit: And I am talking strictly within a recreational aspect of the use of Nitrox mixes; i.e. < 40%] You would need to be sure that the tank is O₂ cleaned so as to avoid any hydrocarbon residuals being in the tank when filling it with nitrox mixes since they have an elevated O₂ level and therefore may represent a higher risk of combustion in the presence of hydrocarbons when being filled using certain filling procedures. Other than that I've dived mine with AL and Steels no problem and I've never run into anyone giving me grief either way.

If, however, you are not only considering your gas mix in the tank but also the difference in buoyancy characteristics between the two, then you might find a reason to prefer an AL above a steel or vice versa.

I say this according to my personal knowledge only and I would gladly defer to perhaps one of the engineers or better qualified mixed-gas tech divers on the board for a more detailed explanation.

 

[SlowRain]

Very quick answer...

Insofar as a basic nitrox (02 not greater than 40%) and if the fill is from a system properly maintained and designed for scuba diving (that is properly dried and cleaned gases) then the difference between AL and Steel is not really a discussion point. Whether or not the cylinder/valve is "nitrox ready" is dependent on the manufacturer (or reseller) ensuring that they have performed the necessary steps (elimination of hydrocarbons) to ensure compatibility with being able to fill with nitrox rather than the cylinder material itself.

Having said all that, after having dove both AL and Steel, for many years, I prefer steel for 2 main reasons, first being the amount of weight I don't have to use with steel that I do with AL, and second steel tanks, properly cared for, have a longer lifespan that AL does. My main tanks are all steel, however I do use AL for stage/deco bottles.

 

[captndale]

Both steel and aluminum tanks may be used equally well with nitrox. The advantages/disadvantages of steel vs. aluminum relate to buoyancy characteristics, maintenance and fill capacity, not to the gas mix.

 

[sotgecho]

Thank you for the responses. It helps a lot.

After reading your responses for me I guess it comes down to a weight issue because I am only doing >40% O2 diving. Right now I only use 10 lb of lead to sink me with an aluminum tank and I think maybe still I am overweighted a bit. So I think spending the extra money on a steel tanks would work better for me in the long run.

 

[Melicertes]

Thank you for the responses. It helps a lot.

After reading your responses for me I guess it comes down to a weight issue because I am only doing >40% O2 diving. Right now I only use 10 lb of lead to sink me with an aluminum tank and I think maybe still I am overweighted a bit. So I think spending the extra money on a steel tanks would work better for me in the long run.

I'm assuming the >40% was a typo and you meant < 40%?

 

[dannobee]

Well, there's one aspect that others haven't mentioned yet. If you're diving Nitrox, chances are that you'll be staying down longer because of the increased NDL's. With an AL 80 tank, you could run out of gas long before you run out of NDL, obviating the need for Nitrox in the first place (unless you consider the "safety" of Nitrox a major driver in your decision).

The vast majority of steel tanks are larger than aluminum tanks, and would be better at helping you increasing bottom time without going into decompression.

Get a big steel tank, fill it with the proper mix for your dive, and have fun.

Buoyancy characteristics of steel tanks vary, and you might be dropping 5 lbs of lead and have a tank with a LOT more capacity than an aluminum 80.

 

[sotgecho]

I'm assuming the >40% was a typo and you meant < 40%?

Definitely a typo.

 

[Bubbletrubble]

I agree with everything that's been posted. To expand on what was mentioned by danobee, you should also probably consider how much weight you need to carry on your rig to be properly weighted, the distribution of the weight for optimal trim, and how much of it should be ditchable.

OK. I'm now going to channel my high school chem teacher, so that I can go off on a science tangent...
You probably already know this, but "Fe" is the chemical signal for "iron" not steel. Steel is not an element at all but an alloy consisting of a mix of iron (Fe), carbon (C), manganese (Mn), silicon (Si), sulfur (S), phosphorus (P), vanadium (V), molybdenum (Mo), and chromium (Cr). As far as I know, different steel alloys can be made by varying the mix of the aforementioned elements. (I realize that by making this point I'm opening myself to the scrutiny of all lurking ScubaBoard chemists.)

Have fun and dive safe.

 

[pescador775]

Continuing on the above logic, aluminum alloy is not "Al". Those tanks are made of a heat treated alloy consisting of Al, Cu, Zn, Si, etc. Unlike the moniker "steel", the given names of various aluminium based metals like Duralumin did not stick as well in the public mind, probably because they were confusing. Some metals such as the chrome nickel iron alloy called "18-8 stainless steel" are not technically steels at all (no carbon).