What are the advantages or disadvantages of steel vs aluminum scuba diving tanks?
They are both excellent but you need to compare several features.
What is the size of tank and the pressure required to get to full
capacity. Some dive boats and some stores wont fill past 3000 psi
on a tank. I was on one boat that could barely get us to 2600psi.
Those divers that required a 3400psi fill on their steel tanks to
get to capacity had to shorten their dive times. It used to be a
big factor that one tank was more bouyant than another or one less
bouyant. Today we have neutral tanks in both aluminum and steel so
this is no real factor these days. Even the non neutral tanks dont
make that much difference. I both a steel and an aluminum and I
carry the same weight either way. Steel is more expensive and can
do a 10 % overfill for a period of time. But you need to watch
because some say they are an 80 after the overfill. So once you
cant over fill you will have a smaller tank. Size for the cu. ft.
value I always found the steel to be smaller. So an steel 80 was
smaller in size than an aluminum 80. If you were carrying dual
tanks this was a great advantage. For the regular sport diver not
so much so. Its steel so it can rust. When I inspected tanks it was
always the steel tanks I failed because moisture got in, for many
reasons, and rusted the tank. Because I cant tell if the rust is
new or old and deep they always have to go in and be cleaned and
tested with any rust. The aluminum stays at its value start to
finish. the 80cu.ft. is standard enough to not worry about some
places not filling it and the inspection of the tank rarely finds a
fault. Its less expensive than its counter part and comes in more
colors. Other than these things I cannot find any reason for one
over the other. My preference as an instructor was always to go for
the aluminum. Price was better and the look and feel was better.
The only people I ever saw benefit from the steel was the deep
divers or the dual tank divers. They got more air for the size and
the weight difference made big differences at depths beyond the
sport diver depths. As for size. An 80 cu. ft. tank can carry most
people thru the length necessary for a savfe dive. At 60 feet you
have @ 60 minutes time to dive. The 80 cu. ft. will last that long
for most people. If you are a heavy breather and can only get 40
minutes at 60 feet then you are a canidate for the 100 or 120 cu.
ft. tank. Rent one and see what your bottom times are prior to
purchasing. My wife breaths less air than I so I have a 72 cu. ft.
tank for her whe we dive together. It failed its testing this year
but my aluminum is going strong. Hope this helps. Jonathon, PADI
Steel tanks can always get the "10% overfill" as long as it is
requested during its hydrostatic test and if it passes. Steel is a
stronger metal than aluminum. It is virtually impossible to put a
deep scratch in a steel tank, but it is very easy to do on an
aluminum ... which could condemn the tank. Since aluminum is a
softer metal, it requires more material to hold the pressure.
Because of this, aluminum tanks are bigger than steel (as well as
heavier out of the water) to hold the same amount of air. They also
have to be pressurized more since the internal valume is less due
to there needing to be more aluminum to hold the pressure. An
aluminum "80" is not really an 80 and really is more like a 77, so
you can not go off of common names to know how much air a cylinder
will hold. So to summarize, steel is more durable, lighter out of
the water (compared to the same volume aluminum tank), more
negative in the water (so you need less weight on your weight belt)
and smaller. Of course you can get a steel tank that is larger and
holds even more air. The main down side to steel tanks are that
they are more expensive, but I find the advantages outweigh the
expense. Any rust in a steel tank would be on the inside and only
results from bad fills (so go to a good fill station) or draining
your tank all the way (so don't do it). The risk of rust is small
if they are cared for and any rust can also be tumbled out.