Aluminium vs Steel
A comparison of Luxfer AL80 vs Faber Steel 12L
Aluminium tanks are more corrosion resistant because a thin layer of aluminium oxide forms if the bare metal is exposed to air (eg scrapes). This provides better salt resistance than steel, which makes it more desirable for resorts internationally. However, steel is stronger than aluminium so metal fatigue is less for steel, which gives them a potentially longer working life than aluminium (provided corrosion doesn't get them first).
Aluminium tanks are heavier than steels per unit gas carried, when above water. There are several reasons for this. Firstly, more metal is required to make an aluminium cylinder so despite the lower density, it is still heavier than an equivalent steel cylinder. Without valves, a Luxfer AL80 cylinder weighs 14.3kg whereas a Faber 12L steel cylinder weighs 13.1kg. Secondly, the internal volume of the AL80 cylinder is 11.1L, as opposed to 12.2L for the Faber steel. Thirdly, the working pressure for an aluminium cylinder is 207bar as opposed to 232bar. Assuming ideal gas laws, the AL80 contains 2297.7L while the Steel 12 holds 2830.4L of gas. Compared to an AL80, a Steel 12 carries 23% more gas for 8% less weight. It is also (as previously mentioned) lighter in absolute terms.
Underwater, both types of cylinder will be negatively bouyant (and sink) when full. However, an AL80 will be less negative than a Steel 12. Both tanks will become progressively buoyant (at the same rate) as gas is consumed. When empty, both types of cylinders will float. Assuming good gas practice and 500g-1kg of hardware (valve, first stage, various gauges, and 2nd stages), I would expect a Steel 12 to be just negative at safety stop and an AL80 would be about 1-2kg positive. So carrying a AL80 will require you to add 2kg (probably 2.5kg as you will be carrying 600g less gas at the start) compared to a Steel 12.
The almost neutral characteristic of an AL80 is hugely advantageous if you have to manoeuvre the tank in water. Moving it from one attachment to another does not affect trim, only cross section profile. Handing off or clipping off rarely requires adjustment to the bouyancy compensator. Sidemounters can swing both tanks forwards without affecting trim, and can dive single sidemount without compensating.
In summary, Steel 12 is lighter, carries more gas, takes lead off your belt, and may last longer. AL80 corrodes less in salt environment, and is much less cumbersome to handle underwater. It has nice flat bottoms that allow it to stand upright without a boot. It is also the commonest cylinder we will encounter abroad.
A comparison of Luxfer AL80 vs Faber Steel 12L
Aluminium tanks are more corrosion resistant because a thin layer of aluminium oxide forms if the bare metal is exposed to air (eg scrapes). This provides better salt resistance than steel, which makes it more desirable for resorts internationally. However, steel is stronger than aluminium so metal fatigue is less for steel, which gives them a potentially longer working life than aluminium (provided corrosion doesn't get them first).
Aluminium tanks are heavier than steels per unit gas carried, when above water. There are several reasons for this. Firstly, more metal is required to make an aluminium cylinder so despite the lower density, it is still heavier than an equivalent steel cylinder. Without valves, a Luxfer AL80 cylinder weighs 14.3kg whereas a Faber 12L steel cylinder weighs 13.1kg. Secondly, the internal volume of the AL80 cylinder is 11.1L, as opposed to 12.2L for the Faber steel. Thirdly, the working pressure for an aluminium cylinder is 207bar as opposed to 232bar. Assuming ideal gas laws, the AL80 contains 2297.7L while the Steel 12 holds 2830.4L of gas. Compared to an AL80, a Steel 12 carries 23% more gas for 8% less weight. It is also (as previously mentioned) lighter in absolute terms.
Underwater, both types of cylinder will be negatively bouyant (and sink) when full. However, an AL80 will be less negative than a Steel 12. Both tanks will become progressively buoyant (at the same rate) as gas is consumed. When empty, both types of cylinders will float. Assuming good gas practice and 500g-1kg of hardware (valve, first stage, various gauges, and 2nd stages), I would expect a Steel 12 to be just negative at safety stop and an AL80 would be about 1-2kg positive. So carrying a AL80 will require you to add 2kg (probably 2.5kg as you will be carrying 600g less gas at the start) compared to a Steel 12.
The almost neutral characteristic of an AL80 is hugely advantageous if you have to manoeuvre the tank in water. Moving it from one attachment to another does not affect trim, only cross section profile. Handing off or clipping off rarely requires adjustment to the bouyancy compensator. Sidemounters can swing both tanks forwards without affecting trim, and can dive single sidemount without compensating.
In summary, Steel 12 is lighter, carries more gas, takes lead off your belt, and may last longer. AL80 corrodes less in salt environment, and is much less cumbersome to handle underwater. It has nice flat bottoms that allow it to stand upright without a boot. It is also the commonest cylinder we will encounter abroad.
