High Pressure Aluminum

[scubafanatic]

Aluminum does not rust, it oxidizes. Further, aluminum in a salt water environment corrodes and will pit. It just like steel needs to have some level of protection.

I've seen many a fleet of highly used/abused AL 80/63's in tank filling stations/farms in hot, humid, tropical salt water environments (Cozumel and Bonaire come to mind) and never noticed what you describe. Those tanks are rode hard, put away wet, totally neglected in highly abusive rental conditions....you notice you don't see steel tanks in these tank farms, do you?

 

[Rred]

Easy answer: Divers are cheap. Aluminum tanks are WAY CHEAPER than steel tanks. And that's how the mass market goes. Rental shops that need to buy maybe 50-100 tanks at a time? Would rather buy the tanks that are popular and familiar to their customers--the aluminum tanks--and while they are at it, save maybe $100 per tank on 50-100 tanks. It adds up!

The mass market things aluminum is better because it is LIGHTER and MODERN compared to those old steel tanks. Some of us know the difference between the steak and the sizzle, and stick to steel.

 

[Blasto]

Easy answer: Divers are cheap. Aluminum tanks are WAY CHEAPER than steel tanks. And that's how the mass market goes.

That is not the only difference.
That is BY FAR not the only difference.

Steel tanks can deform or lose a considerable amount of integrity when dropped or strongly dinged. Aluminum tanks don't. This is a big deal in always under-monitored commercial DC operations.

Aluminum corrodes much, much slower than steel. Here is a comprehensive study done by the Navy of just about every metal in seawater: www.dtic.mil/get-tr-doc/pdf?AD=ADA021279

You will find both 4130 and 6061 in there. Note how 4130 (and that's one of the more-resistant cylinder steels) has over twice the corrosion rate of 6061, over 2 mpy vs around 1 mpy in most tests. Design rules specify even more difference in corrosion allowance for steel over aluminum. And as if that wasn't enough, aluminum scuba tanks are three times the thickness of steel.


Price is not the deciding factor. Plenty of dive shops buy more expensive stuff for their rental than they have to. The $80 difference between AL80 and HP80 is peanuts compared to buying Sherwoods, shorties, full-foot fins vs AL Titan, full suits, booties, "deluxe" jackets, etc., and all of the latter lasts much less than the tanks.

 

[Magnus Lundstedt]

For me its not so much a matter of price, its not that big difference here.

If i dive dry, I use steel tanks, then i do not need as much weight.

If i would use my warm water setup (2/3mm wet) together with my steel 12l I would have to drop more weight than i carry.

Difference in boyuancy between a long 12l steel and a AL80 is about 4.5kg, i carry 2-3kg lead in salt water with an AL80. diving at home means fresh or very light brackish water, that means i would have to drop about 3kg more.


At home i dive dry with steel tanks, tropical i dive wet with al tanks, easy.

 

[runsongas]

wholesale price for luxfer al80 is significantly lower. aluminum does resist corrosion a bit better,

Problem with that theory is 2008 is about the same time PST went out of business! Worthington went out of business shortly thereafter (about 2012)...so if hot-dipped galvanized tanks are so 'hot'/superior, what's your theory on that ? Don't get me wrong, I own 16 hot-dipped galvanized HP tanks (PST and Worthington), but somehow they failed in the market.

faber brought back HDG tanks because there is enough demand where divers prefer it over their triple painted tanks. the pst/worthington tanks were always a popular choice in the US/CA when available, but the quantity sold was too low to make it viable as a standalone business. Faber benefits from having a large market share in the EU and commonwealth countries that pst/worthtington never had.

 

[runsongas]

aluminum tanks are more resilient to poor maintenance and handling by dive shops and cheaper to buy. that is why they became more popular. steel 72s were the de facto tank for a while till the 80s when standards sank like the titanic.

 

[Blasto]

aluminum does resist corrosion a bit better,

A lot better. About an order of magnitude.

wholesale price for luxfer al80 is significantly lower.

So it is for steel.

It's not about the price, that difference is trivial compared to the overall cost of diving. Lots of EU shops do use steel.

The dominance of AL tanks coincided with the rise of tropical vacation diving. Board shorts are a perfectly fine exposure suit in the tropics, unlike 5-7 mm that usable suits start at in the EU or the US, so there's no positive buoyancy you need to offset with steel. You just need a couple weights on the belt, which you want your customers to wear for safety anyway.

If a customer goes in with an empty steel and no suit, they'll have zero or negative buoyancy and no way to get positive. That's bad. With aluminum, they always have air to inflate, weights to drop, or they're positively buoyant to begin with.

A steel HP80 rig is three or four kilos lighter than an AL one, but you're not a dive op on a tropical island without a boat. However easy the shore entry, you go by boat. The boats don't care and there's plenty of cheap DMs to help elderly or less-capable customers.

Steel simply doesn't make sense for tropical diving. The couple kilos it saves and slightly better trim aren't worth dealing with its finicky and necessary paint, corrosion, which is much faster in the tropics, and damage from drops.

 

[runsongas]

Steel 72 is neutral when empty and sufficiently small it can be offset by using lung volume to counteract the weight. A steel 72 is great for diving in the salt even with no wetsuit. Hdg tanks do not use paint. Corrosion and drop damage for steel tanks can be avoided with proper maintenance and care in handling. Aluminum has significant advantages, but they are due to cost and ease of ownership and not actual performance. Steel is still superior for weight to capacity, buoyancy, and size to capacity for backgas, but those considerations aren't as valued by dive shops.

Privately owned backgas tanks are more likely to be steel vs rental al80s just like some might have a mustang GT in their garage vs a Corolla on the rental car lot.

Hp80 is also a non ideal tank vs lp72/85 or hp100

 

[swimlikethefish]

How are those 72's that DGX sells? The metal impact aluminum ones? Anyone use them?

 

[Tug]

How are those 72's that DGX sells? The metal impact aluminum ones? Anyone use them?

I use both AL80’s and AL72’s for bailout with my rebreather and prefer the72’s. I don’t have any scientific proof but for me they just seem to ride better when I’m slinging two bottles.