Cave Filling LP versus HP tanks

[Charles2]

3aa spec is low carbon steel that is lower tensile strength but better elasticity. the higher elasticity allows it to tolerate the additional stress of overfills better so that it doesn't fatigue prematurely and fail their next hydro.

most 232 bar / 300 bar / 3442 psi tanks are made from high carbon steel which makes them stronger/tougher and thus have thinner walls/lower weight for a given capacity/service pressure. but their lower elasticity means more risk of permanent deformation at higher pressures and more likely to lead to premature failure at their next hydro.

The Authorized Materials in the 3AA spec, also in the SP-13488 spec, and used by most manufacturers are not considered 'low carbon' steels (0.05 to 0.25 percent carbon) but rather 'medium carbon' alloy steels (0.30 to 0.80 percent carbon) If one can believe their advertisements, most manufacturers of 3AA tanks say they use a 4130 steel which has a very similar composition to the steels used in the DOT-SP 13488 spec. According to my research, I have not found a manufacturer that uses a 'high carbon' specification.

 

[geoscience]

LP 95's are the same dimensions as 117's, so when filled to over 3000, it's a lot of gas. I have a set that are too heavy for me since surgery. Selling them or trading them.

 

[Scared Silly]

I've heard the story go a dozen (rough numbers) times "This LP cylinder is identical to the one they ship to Europe for 300 bar service and they just stamp it different here because the manufacturers are scared of law suits."

...no literature or sources.

Yeah and the story is bull excrement ... do a search of the posts by Lee from SeaPearls who did the importing early on before Blue Steel.

 

[2airishuman]

3aa spec is low carbon steel that is lower tensile strength but better elasticity. the higher elasticity allows it to tolerate the additional stress of overfills better so that it doesn't fatigue prematurely and fail their next hydro.

most 232 bar / 300 bar / 3442 psi tanks are made from high carbon steel which makes them stronger/tougher and thus have thinner walls/lower weight for a given capacity/service pressure. but their lower elasticity means more risk of permanent deformation at higher pressures and more likely to lead to premature failure at their next hydro.

This is imprecise (what do you mean by "elasticity?") and not true, as the carbon content is similar.

Does sound logical.
Cameron

"For every complex problem there is an answer that is clear, simple, and wrong." -- H.L. Mencken

 

[NAM001]

Thankfully it's a rarity.

...but of course they adopt no burst disk like your side of the pond.

Funny how often I hear the argument in the Americas that it's Europe that does "cave fills" as regular service pressure.

I get nervous diving around the 100$ Chinese carbon fiber tanks I'm seeing on some rebreathers. (That's another story)

A healthy respect for gasses under pressure is good for our longevity.

the difference may be in the nations assigned safety factor. America it is 4 other nations is 3 and 2.5.

 

[Storker]

the difference may be in the nations assigned safety factor

I used to belive that. But then I learned:

Test Pressure is stamped on the tank and for 3442 PSI tanks is 5250 psi

IOW, test pressure for HP tanks in the US is 150% of service pressure. Just as it is in (my part of) Europe.

 

[NAM001]

I used to belive that. But then I learned:


IOW, test pressure for HP tanks in the US is 150% of service pressure. Just as it is in (my part of) Europe.

test pressusre is 5/3s not 150% in the US. unless indicated.

 

[Storker]

test pressusre is 5/3s not 150% in the US. unless indicated.

That's 5735psi test pressure for a 3442psi service pressure tank. That's a bit more than the 5250psi claimed by @Charles2 .

 

[Charles2]

test pressusre is 5/3s not 150% in the US. unless indicated.

Test pressure for 3AA tanks is 5/3 service pressure.

Test pressure for SP-13488 exemption tanks (i.e. HP-3442 psi service pressure) is stamped on the crown of the tank and is 5250 psi.

the difference may be in the nations assigned safety factor. America it is 4 other nations is 3 and 2.5.

If, by 'safety factor' you mean the relationship between service pressure and burst pressure, then your statement is not accurate. The SP-13488 specification requires that "Cylinders subjected to the burst test must withstand a pressure of at least 2.25 times the service pressure without failure."
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[NAM001]

Test pressure for 3AA tanks is 5/3 service pressure.

Test pressure for SP-13488 exemption tanks (i.e. HP-3442 psi service pressure) is stamped on the crown of the tank and is 5250 psi.

If, by 'safety factor' you mean the relationship between service pressure and burst pressure, then your statement is not accurate. The SP-13488 specification requires that "Cylinders subjected to the burst test must withstand a pressure of at least 2.25 times the service pressure without failure."
​

do you now by chance what the safety factors are for al and 3aa, mayber it is the reason why it is a SP tank.