Regardless of whether you’re planning on purchasing your first scuba diving tank, or just curious to know the differences between aluminum and steel scuba tanks, this articles got you covered.
We’ll explain the difference between both tank types, so you know which one to buy or take on your next dive.
To get started, let’s take a look at the physical attributes of these tanks.
Aluminum is a much softer material than steel.
Do you remember squashing soda cans when you were a kid?
While an aluminum tank is reinforced much more than a soda can, the metal will scratch and dent much easier than a steel tank would.
This relative frailness can cause cracks in your tank, especially where it’s threaded and attachments screw onto it, rendering it unusable.
Aluminum tanks should be inspected regularly for cracks in order to prevent them from becoming unsafe for use.
While aluminum does not rust when exposed to moisture, it does corrode, creating an aluminum oxide, which interestingly enough, can help it become more resistant to the elements.
Now it’s steel’s turn.
If you remember anything from chemistry class, steel is composed of mostly iron as well as some carbon and trace elements.
Iron is very prone to rust, especially when exposed to moisture, which, of course, is unavoidable when diving.
To prevent this, steel tanks require extra care to prevent deterioration. This extra care entails ensuring your tank is only filled with dry air and is never completely drained of air.
Careless dive centers or compressor users can sometimes add wet air into your tank. In the event rust is discovered on your steel tank, it’s time to tank it in for inspection where it will be tumbled.
So in the durability department, steel wins, if you can keep it rust-free.
Tank Size and Weight
When it comes to the weight of your tank, which can be a pretty important factor, steel tanks are often lighter than aluminum cylinders.
This might seem counterintuitive at first as steel is a much heavier material, but due to the alloy’s increased strength, more aluminum is used to reinforce the tank walls, than in a steel tank.
A standard dry steel tank will weigh around 28 pounds, whereas a standard dry aluminum tank will weigh around 33 pounds. In addition to this weight difference, standard steel tanks are often slightly smaller and thinner than standard aluminum tanks.
Notice how we made sure to include “standard” in the previous paragraph when discussing the size and weight of steel and aluminum tanks?
This is because when we start discussing tank variations (specialty tanks) with varying pressure capacities in the next section, we may encounter exceptions to the expected rules.
Tank Capacity and Pressure
The capacity of a scuba diving tank is directly correlated to its rated pressure.
Generally speaking, standard steel tanks store the same amount of air as standard aluminum tanks, although steel tanks have the added ability to be overfilled, as long as their recent inspection allows for that.
You might see the signs HP (High Pressure) and LP (Low Pressure) thrown around when shopping for tanks. So depending on how the tank is built, a certain material type will hold more or less air than expected.
High-pressure steel cylinders can push past ~3400 PSI but need extra thick tank walls to support the pressure, causing them to be heavier than their aluminum tank counterparts. Most regulators can only support up to 3000 PSI, so again, make sure all of your gear is compatable.
Another thing to note when comparing both tank types is the types of valves they will come with.
Newer tanks are usually compatible with both tank types, but for older tanks, steel tanks tend towards DIN valves whereas aluminum tanks tend to gravitate towards yoke valves.
This distinction is important to think of when shopping for a regulator and a tank, as you’ll want both of them to be compatible.
Another comparison we want to look at when it comes to steel tanks and aluminum tanks is their buoyancy characteristics.
Steel is a much more dense material than aluminum, so for that reason, steel tanks are much more negatively buoyant.
This difference is only exacerbated as your dive continues.
Aluminum tanks will become positively buoyant, while a steel tank will become less negatively buoyant as the dive continues. A steel tank will always be negatively buoyant in water even when it’s empty.
To compensate for this, most divers with aluminum tanks need to bring more weight with them than a steel tank diver would. This is why steel tanks are most commonly used for colder water diving and in warmer water dive locations you’ll find aluminum tanks.
When you’re diving in colder water you’ll need to wear more weight to compensate for the buoyancy of a thicker wetsuit, wetsuit undergarments, or drysuit.. By using a steel tank you can wear less weight which is much more comfortable. If you like to have less weight on your weight belt or integrated weight pockets, this could be a deciding factor for you.
The OtterAquatics buoyancy calculator can help you plan around this and wear the correct amount of weight for your dive.
As you can probably guess by this point, steel diving tanks are going to be more expensive than aluminum tanks upon first purchase. If price is the ultimate factor (scuba is not the hobby to skimp), then go with an aluminum tank.
We expect a steel tank to be on average 30%-100% more expensive than an aluminum tank.
Considering we mentioned above that steel tanks are more durable than aluminum, it could pay off, in the long run, to pay the increased price now and save in the long run.
Regardless, in the long run, purchasing your own scuba tank will bring down the cost of diving for you over time, as you’ll no longer need to pay rental prices.
Lastly, consider getting a used tank if the person selling it is reputable and the tank was inspected recently. Inspection requirements vary slightly in different countries but PADI recommends that your scuba tank is visually inspected (both inside and out) every year and has a full service every 5 years.
When a tank has a full service this is marked on the outside with the month and year so you can always check if you are unsure.
To recap, when it comes down to tank durability, steel tanks generally win out over aluminum tanks, as long as they are prevented from rusting by only using dry air and never letting them drain all the way.
Capacity between the two tank types can vary, depending on if a specialty scuba tank is being used, but all else considered, steel slightly wins out due to the ability to overfill them.
When it comes to buoyancy control, steel tanks and aluminum tanks behave slightly differently. Steel tanks are pretty much always negatively buoyant whereas aluminum tanks start negatively buoyant and become positively buoyant when approaching empty. In colder waters steel typically wins out whereas in tropical environments aluminum tanks win.
The main area where an aluminum tank is a clear winner is in the price department, where they are much cheaper than a steel tank.
Overall, picking which scuba diving tank comes down to personal preference and the situation at hand. Steel and aluminum tanks will both get the job done, as long as their strengths and weaknesses are planned around accordingly.
Which type of scuba tank are you going to get?
Let us know in the comments!