Effect of Hot Fills on Tanks

[lamont]

When the tank cools its pressure will have dropped.
If it is at 60C when filled 200 bar and it cools off to 20C, the pressure will drop to 176 bar. There is a temptation to overfill to compensate!

The temptation is perfectly fine. Tanks must cool to at or below their rated fill pressure at 70F, but you can go up to a 25% overfill at 130F (although the ideal gas law suggests that anything over 17.5% at 130F will cool to an overpressure at 70F if I'm doing my math right...):

173.301(e) Container Pressure. The pressure in the container at 70 degrees f must not exceed the service pressure for which the container is marked or designated except as provided in 173.302(c) [173.302(c) describes the "10% overfill" allowed for some steel cylinders
173.301(f) Container pressure a 130 degrees f. The pressure in he container at 130 degrees f shall not exceed 5/4 times the service pressure.

 

[ClayJar]

I have read it.

As had I. I was just posting it so I didn't leave a dangling reference.

 

[Hoosier]

I hope I can use my steel tanks until getting any structural damage due to the hot fill.

How many cycle does the steel tank last? more than 10,000 cycles... LOL~~~

 

[lamont]

I hope I can use my steel tanks until getting any structural damage due to the hot fill.

How many cycle does the steel tank last? more than 10,000 cycles... LOL~~~

I think I may have cold tanks which are 3600-3700 psi out in the back of my car, I better go bleed them off.... as i type these words they may be getting the magic >3500 psi cracks that hydros can't detect...

 

[Hoosier]

I think I may have cold tanks which are 3600-3700 psi out in the back of my car, I better go bleed them off.... as i type these words they may be getting the magic >3500 psi cracks that hydros can't detect...

Yours might be, not mine!

Even though I dived every weekends, I don't think I can have more than 2,000 cycles within 10 years. This subject has been covered on our board many times as you may know.

It is too much worry in my perspectives.. Maybe it is due to the system of this society, such as, insurance, lawsuit, etc.

 

[CompuDude]

Yours might be, not mine!

Even though I dived every weekends, I don't think I can have more than 2,000 cycles within 10 years. This subject has been covered on our board many times as you may know.

It is too much worry in my perspectives.. Maybe it is due to the system of this society, such as, insurance, lawsuit, etc.

I can tell you that my PST HP100 (true 3500psi DIN skinny-neck model manuf. 9/01) failed hydro a month ago due to over-expansion under pressure. Tech was a buddy, he tried it 3 times to get it to pass, but no dice. His suspicion was repeated overfills by the original owner (I bought used at a swap meet in Feb '06). I don't think a 3600-3700 psi overfill is a concern, but who knows how high it was taken. That tank should have lasted another 20 years.

Or maybe it was just a bad tank. *shrug*

 

[Hoosier]

I can tell you that my PST HP100 (true 3500psi DIN skinny-neck model manuf. 9/01) failed hydro a month ago due to over-expansion under pressure. Tech was a buddy, he tried it 3 times to get it to pass, but no dice. His suspicion was repeated overfills by the original owner (I bought used at a swap meet in Feb '06). I don't think a 3600-3700 psi overfill is a concern, but who knows how high it was taken. That tank should have lasted another 20 years.

Or maybe it was just a bad tank. *shrug*

Sure, nothing is perfect (100%).

All Japanese car is worry free and reliable? Nope
All American car is crap, endless defect, or breakdown? Absolutely not.

Like you said, it might be bad batch or actual damage due to the overfills though.

But, how often can you see the hydro failure due to the overfill? It is more common to see the hydro failure in cave country? So, many active cave divers are try to get rid of their HP or LP tanks before renewing the hydro?

Seriously, I don't know...

But, I am ready to be happy to see the hydro failure of my tanks after having a lot of cave diving (overfill)


BTW, please let me know if you want to get rid of HP100

 

[CompuDude]

Sure, nothing is perfect (100%).

All Japanese car is worry free and reliable? Nope
All American car is crap, endless defect, or breakdown? Absolutely not.

Like you said, it might be bad batch or actual damage due to the overfills though.

But, how often can you see the hydro failure due to the overfill? It is more common to see the hydro failure in cave country? So, many active cave divers are try to get rid of their HP or LP tanks before renewing the hydro?

Seriously, I don't know...

But, I am ready to be happy to see the hydro failure of my tanks after having a lot of cave diving (overfill)

BTW, please let me know if you want to get rid of HP100

I wish! They condemned the tank and destroyed it. No one would have filled it anyway.

I don't know what the overall failure rate is, and yes, it could have just been a bad tank, but for me and my wallet, that once was enough. I'm happy to gamble with rental tanks should I travel to cave country and be offered overfills, but for my own tanks I'll keep it to the 3500psi (cold) or the +25% for hot fills... on those few places around here that will even go that high.

I may have felt different had I not bought the tank with only one year to Hydro, and thus gotten a full 5 years out of it before it was condemned, but $200 is a lot of money for under one year of use, IMO.

 

[Hoosier]

I may have felt different had I not bought the tank with only one year to Hydro, and thus gotten a full 5 years out of it before it was condemned, but $200 is a lot of money for under one year of use, IMO.

I agree.... It must be really PITA.

I meant, get the brand new "tank" and use it with an overfill for 4~5 years........

 

[oxyhacker]

Trying 3 times is illegal and pretty much defeats the whole purpose of the hydrotest, so maybe you were lucky it didn't pass in the end.

However if he wasn't aware of the fact, or didn't care, I got to wonder if maybe he also didn't know how to properly hydro an HP in the first place.

BTW, did they have your permission to destroy it? If they didn't, they had no business doing so.

Tech was a buddy, he tried it 3 times to get it to pass, but no dice.

I wish! They condemned the tank and destroyed it.