What are the advantages or disadvantages of steel vs aluminum scuba diving tanks?

Steel vs. Aluminum Scuba 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 instructor

Addition

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.