calculating the velocity of a component if burst during pressure testing 1

[costa1205]

Hello, I am new to this forum and I am designing a Pneumatic Pressure testing system for a double ended DOT 3E 1800 cylinder that is fitted with two needle valves and a quick connect fitting. The sizes of the nozels are all 1/4".

We are looking to pressure it up to 1800 psi with air, while it is placed in a tank full of water so we can open and closed the valves to see if there is any sign of leakage.

I was wondering how I could calculate the velocity a fitting would have if it were to fail. I need this velocity in order to decide what kind of material I can use for the tank itself.

Here is a picture of the set up

 

[EdStainless]

For an upper limit use the speed of sound in air at your temp and pressure. That is all the faster that air can expand so it sets the max velocity
The you can estimate the drag of the water and come up with an impact energy.

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Plymouth Tube

 

[Duwe6]

I would consider making the tank out of 12-gage stainless [no rust into the water], and put SA-516 Grade 70 plate on the outside. The only areas of concern are where you cannot have shrapnel flying. I'd put a 3/4" thick plate on those sides, and plug-weld the s/s to the c/s plate - probably a 2 to 3-ft staggered 'checkerboard' pattern.

Carbon steel is fairly cheap, and any good vessel shop will have CNC plasma and/or acetylene cutting ability. Draw up your box, and order the plate.

 

[costa1205]

Duwe6, What do you mean by a 2 to 3 ft staggered checkerboard pattern?

 

[Guest102023]

Fast enough to seriously harm an innocent bystander.

Next question.

 

[costa1205]

@btimstoner, well obviously, that is why I want to make a strong enough enclosing for it.

 

[costa1205]

I also found this:

"The stored energy may be calculated using the following formula providing that nitrogen
or air is used as the test medium:
E=2.5 x Pat x V [1 (Pa/Pat)0.286 ]
Where:
E = stored energy in kJ
Pa = absolute atmospheric pressure, 101 kPa
Pat = absolute test pressure in kPa
V = total volume under test pressure in m3"

Does this seem the correct energy release I could excpect if burst? is that what I should have my walls rated at?

 

[SNORGY]

In the worst case, one might assume that 100% of the stored energy is available for instantaneous release local to the part being blown away. If one assumes all of this potential energy is transferred to the kinetic energy of the blown-away part, for which the mass needs to be known, initial velocity can be estimated.

Trouble is, not all of the PE will be instantaneously released and transformed to the part's KE; it will be apportioned between the rest of the assembly and there will also be some break-away energy that will not be transferred to the part's KE.

If the tank is big enough this might not be an issue anyway. Googling videos about firing a gun under water shows that the bullet only travels a bit over a yard through the water before it comes to a dead stop. If the container can withstand the concussion, it can probably withstand the impact of the projectile.

 

[EdStainless]

A larger tank gives a lot of safety margin, but you must test deep in it, at least a couple of feet, otherwise you would need a strong lid also.
You will want a lid. If this bursts you will blow a 100 gal of water up out of the tank and a lot of people (anyone withing 50') will be mad at you.

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Plymouth Tube

 

[HotStab]

Costa,
It seems that you are concerned with missiles and not with a catastrophic vessel failure. In missile assessment the storage energy in the vessel is also an important input, but other constraints shall be also considered.
Take a look on the British report CRR 168, it is a very valuable reference for this issue.

http://www.hse.gov.uk/research/crr_pdf/1998/crr98168.pdf

Regards,
HotStab.