tank size and pressure

[tbone1004]

@Storker
The chart on the wiki page is experimental values reported for air.
Used 300K for temp which is about 80F so close enough, and if you look at the value for 100bar it's .9930 and for 150bar it's 1.0074. It should be 1.00 in the middle, which is somewhere between the ~1500 and ~2200psi reported. 250bar on that chart was 1.0669 which is about 3600psi, so 3442 will be a bit lower than that.

This is not my area of expertise, so again, the assumptions are coming off of the experimental data reported there, and the fact that a pressure vessel manufacturer *who hopefully has people on staff where this is actually their area of expertise*, have reported two tanks with identical internal water volumes and the high pressure version has a reported nominal volume that matches that chart. That to me says that we can probably believe the manufacturer.
I have requested the drawings for both of these tanks if anyone is still concerned about whether they are actually the same water volume or not

 

[victorzamora]

If I use the van der Waals equation of state and the vdW constants listed by Wikipedia for O2, N2 and He, I get the following compressibility factors.

So, just to clarify some things for me: Would you mind calculating and posting the true amount of gas in a tank with 17L internal water volume at pressures of 100bar, 150bar, 200bar and 242bar with EAN32 and Tmx 10/70?

 

[tbone1004]

@Storker to add to @victorzamora 's request, since I assume the values quoted by Faber are air and the chart I was referencing was in air, if you could post that as well.

Keep temp at 300K as well. Cave country probably averages 80F anyway

 

[NAM001]

and with all gentleness and respect, that is why I won't consider any used tanks from Florida, especially any that have been doubled. I understand tanks are built with a safety factor, and burst disks are a first line of defense. But you're overfilling your tanks to over 150% pressure rating, it's just not good for longevity.

This is just hypothetical for the purpose of my comment. Lets say that 2 tanks are exactly the same. one is made for the US and it is also sold in another country because its design specs are acceptable to their standards. They test the tank and it will blow at 10k psi. the US says 4:1 safety factor which means working pressure is 2500 another country says 2.5:1 safety factor and they assign working pressure as 4Kpsi. which tank is over filled which is under filled? which is the safer tank and which is more dangerous. The only difference ends up being the stamp on the neck that complies to requirements of the nation the tank is marketed in. Those standards are identified with the DOT and CT markings int he US. Differences is standards do not change the tank at all.

 

[NAM001]

So, just to clarify some things for me: Would you mind calculating and posting the true amount of gas in a tank with 17L internal water volume at pressures of 100bar, 150bar, 200bar and 242bar with EAN32 and Tmx 10/70?

Does that really matter at those presures?

 

[2airishuman]

@2airishuman all hydro shops are trained to put the + stamps on. Very few are motivated enough to look up the REE values, or they may not be available anymore like some of the PST tanks which is why the values are stamped on many of the newer tanks.[/QUOTE]

One of my local hydro shops (Nardini) "doesn't do + ratings" and say it is because they don't have the training.

They are otherwise a great shop. Most of the LDSs use them for everything except LP steels.

 

[2airishuman]

This is just hypothetical for the purpose of my comment. Lets say that 2 tanks are exactly the same. one is made for the US and it is also sold in another country because its design specs are acceptable to their standards. They test the tank and it will blow at 10k psi. the US says 4:1 safety factor which means working pressure is 2500 another country says 2.5:1 safety factor and they assign working pressure as 4Kpsi. which tank is over filled which is under filled? which is the safer tank and which is more dangerous. The only difference ends up being the stamp on the neck that complies to requirements of the nation the tank is marketed in. Those standards are identified with the DOT and CT markings int he US. Differences is standards do not change the tank at all.

Except that none of that is true. The safety factor, that is, the ratio of the authorized fill pressure to the expected burst pressure, is about 2.26:1 for + rated 3AA cylinders.

Here's the rules for 3AA cylinders (LP steels), for reference:

eCFR — Code of Federal Regulations

For a typical LP steel rated 3AA2400, here are the relevant pressures:
Rated working pressure: 2400 psi
Authorized fill pressure with + rating: 2640 psi
Test (hydro) pressure: 4000 psi
Average burst/rupture pressure: 6000 psi

I don't believe there's any evidence to suggest that the same cylinder is sold with different markings in other markets where higher pressure is authorized. The standards differ too much from one jurisdiction to the next, and there's been a great deal of effort undertaken to have the new UN international standard written into law in various countries so that a compatible regulatory environment can exist.

 

[tbone1004]

@2airishuman all hydro shops are trained to put the + stamps on. Very few are motivated enough to look up the REE values, or they may not be available anymore like some of the PST tanks which is why the values are stamped on many of the newer tanks.

One of my local hydro shops (Nardini) "doesn't do + ratings" and say it is because they don't have the training.

They are otherwise a great shop. Most of the LDSs use them for everything except LP steels.[/QUOTE]

that would be them using it as an excuse not to do it. That said, not all LP steel tanks can get their + rating back if the REE value is unavailable. I would argue that most LP tanks out there don't have known REE values. PST won't give them out so unless they have the old charts it's not something they'll be able to do. There is nothing different in the test procedure, it's just comparing two numbers against each other

 

[2airishuman]

. There is nothing different in the test procedure, it's just comparing two numbers against each other

That is the part they say they are not trained to do. And they won't, even if the REE is stamped on the shoulder of the cylinder.

 

[NAM001]

Except that none of that is true. The safety factor, that is, the ratio of the authorized fill pressure to the expected burst pressure, is about 2.26:1 for + rated 3AA cylinders.

Here's the rules for 3AA cylinders (LP steels), for reference:

eCFR — Code of Federal Regulations

For a typical LP steel rated 3AA2400, here are the relevant pressures:
Rated working pressure: 2400 psi
Authorized fill pressure with + rating: 2640 psi
Test (hydro) pressure: 4000 psi
Average burst/rupture pressure: 6000 psi

I don't believe there's any evidence to suggest that the same cylinder is sold with different markings in other markets where higher pressure is authorized. The standards differ too much from one jurisdiction to the next, and there's been a great deal of effort undertaken to have the new UN international standard written into law in various countries so that a compatible regulatory environment can exist.

You did not read closely. I said IF..... the tank meets both nations parameters that each nation will mark the working pressure as per their laws which will be differrent than the US.

I dont buy your source because it is the CFR. The CFR is a regulation and not a design spec. Cfr's also say you have to O2 Clean with 23% O2 in a mix. ans that change is the very proof tI mentioned when I said all it takes is a change in standards with out a construct change. The physics of the tank do not change. The level of governmental protections is all that varies. The CFR I doubt says that the burst pressure must be 600 psi min and may not EXCEED 6500 psi. The real specs comes form the maker. and they may only publish something like burst pressure > 6000 as per 3AA standards to minimize their liabliity.