Cave Filling LP versus HP tanks

[MichaelMc]

Most LP tanks are based on the DOT 3AA specification which is very conservative. HP tank specifications represent exemptions to the 3AA specification and as a result, allow service (working) pressures that amount to a slightly higher percentage when compared to burst pressures.

From the recent cave fill thread, this point of Charles above seems the key point. LP start out more conservative than HP.

 

[taimen]

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."

That should be easy to confirm by comparing empty cylinder tare weights. If they indeed are identical cylinders they should weight the same.
European 300bar cylinders are extremely heavy.

 

[Lobzilla]

300 bar is ~4350 PSI. That's a lot, even in cave country. EU test pressure would be 6525 PSI (50% over service pressure) on these tanks whereas our 3AA 2400 PSI tanks get tested to 4000 PSI (5/3 of service pressure).

Assuming that both tanks were designed so that their test pressure is less but somewhat close to the yield strength of the steel, our 3AA tanks would not survive the test pressure of the EU 300 bar tanks.

I bet that the 300 bar tanks have substantially thicker walls and are therefore heavier that the LP (2400 PSI) and HP (3440 PSI) tanks we have here in the USA under 3AA (plus various exceptions). Our HP and LP tanks are pretty close in weight for similar outside dimension.

 

[Lobzilla]

Most LP tanks are based on the DOT 3AA specification which is very conservative. HP tank specifications represent exemptions to the 3AA specification and as a result, allow service (working) pressures that amount to a slightly higher percentage when compared to burst pressures. There is ample anecdotal evidence regarding the safety of "Cave Filling" (50% overfill) LP cylinders. In reading one manufacturer's exemption specifications, it appears that their HP cylinder could sustain a 35% overfill and not exceed the same percentage of overfill to burst pressure that seems to be common on LP cylinders in 'Cave Country'. Of course, overfilling any cylinder means operating outside of the design parameters and accepting its concomitant risk. I do not recommend the deliberate overfilling of any cylinder. I also do not get too concerned about a slight overfill that cools to service pressure, nor do I get too concerned about a properly filled cylinder that lies on hot asphalt and rises to uncomfortable levels. Again, I do not recommend deliberate overfilling of any cylinder.

+1

What is the test pressure for the 3442 PSI tanks and what exception do they fall under?

 

[Jonny Wishbone]

curious. is there a chart or anyone has made up for LP tanks of what the CF of gas would be for different fill pressures? if so, could someone post...

 

[Charles2]

+1

What is the test pressure for the 3442 PSI tanks and what exception do they fall under?

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

DOT exemption number for Faber is E-13488

 

[Lobzilla]

curious. is there a chart or anyone has made up for LP tanks of what the CF of gas would be for different fill pressures? if so, could someone post...

Take the rated volume of the tank at service pressure, divide by service pressure, and multiply by desired pressure.

I prefer to calculate for every tank a 'tank factor' that represents how many cubic feet every 100 PSI yield. That makes gas planning real easy.

Tank Factor = Rated Volume / Rated Pressure * 100

For Example: My AL80 doubles hold 154 cuft @ 3000 PSI and the tank factor comes out to 5.13 cuft/100PSI. I then call that 5 to make math easier.

If my gauge shows 14 hundred PSI, I have at least 14 * 5 = 70 cuft left (71.87 to be precise).

 

[taimen]

If these 300 bar are the rated/service pressure in the EU

Yes, it is the rated service pressure.
Most common new cylinders in my area are Eurocyliders (ECS) 12 liter 232 bar steels, that are 14 kg empty, 14,5 kg for the concave bottom version.
ECS 12l 300 bar steel cylinder has 17,4 kg empty weight.
232 bar cylinders are much more common.

 

[Storker]

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

So, your test pressure is 150% of service pressure. Just like it is on the right side of the pond.

 

[Bob DBF]

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."

That should be easy to confirm by comparing empty cylinder tare weights. If they indeed are identical cylinders they should weight the same.
European 300bar cylinders are extremely heavy.

Number one presumes that the rumor is true.

Number two, even if they are of equal weight, it does not mean the alloy is the same. In addition I don't know the range of weight and size allowed in a run of tanks.


Bob