Why no stainless steel tank

[jaycanwk]

I'm not a metallurgist but I have asked the same question before, and the answer I was given was that stainless steel is not as elastic as the steel currently used for scuba and would not be able to withstand the fill cycling that scuba tanks go through.

 

[ajduplessis]

Strange thou that a lot of members here then have cylinders 20-50 years old still going strong and passing hydro/vip year in year out!!!

I do know there are some manufactures that are a lot better than others, like faber. Most diver operations here only use steel and there are many old cylinders about in great shape!

 

[Rainer]

I don't think you're reading this thread correctly. It's about STAINLESS steel cylinders not simply steel cylinders. Who are these people with STAINLESS steel cylinders that are 20-50 years old????

Strange thou that a lot of members here then have cylinders 20-50 years old still going strong and passing hydro/vip year in year out!!!

I do know there are some manufactures that are a lot better than others, like faber. Most diver operations here only use steel and there are many old cylinders about in great shape!

 

[ajduplessis]

You are right, my apologies.

 

[scubafanatic]

for what it's worth, a while back here on Scubaboard I'd read the Russians had deployed titanium scuba tanks, which would be pretty cool, but the price would likely be pretty scary!

 

[irishsquid]

Sorry, the rapture has been delayed
:shocked2:

If my tank raptures, I hope I'm not "Left Behind" while at depth.

 

[ajduplessis]

Since I am the one who "missed" the rapture, I am glad that I will get a "second" chance :angel2:

 

[akdeepdiver]

What would really be cool is when someone tries to put Nitrox in a titanium Scuba tank via partial pressure blending. Kaboom

 

[captain]

I believe the Russian titanium cylinders were welded together from 3 pieces. DOT only allows seamless cylinders.

 

[zimmo]

I believe the main issues are weight and cost. Cost has already been addressed here.

Weight - Stainless in general has a lower yield stress compared to steel.

For example, 304 (common stainless) has a yield stress around 30 ksi, while 4130 (steel for tanks) has a yield stress of about 65 ksi.

The weight of the tank is directly proportional to the wall thickness, which is inversely proportional to the design hoop stress (in a simplified way).
If the yield stress goes from 65 ksi -> 30 ksi, you'd expect the stress in the walls at operating pressure to be reduced the same factor (2.2).

Therefore the weight would go up by that same factor, and your 30 lb steel 72 just became a 65 lb stainless 72.

Note that the densities of 304 and 4130 are nearly identical.

Your tank also became ~30 lb negatively buoyant!