Hydrostatic Test Failure Analysis

[mech5]

I'm doing an analysis for hydrostatic testing failure modes. I need to know how to estimate the initial velocity of a hose coupling upon failure. I have all the data nessesary of the goemetry of the hose and the pressure at failure.
Thank you.

 

[Duwe6]

How much air was left in the system when the hydro pump was started? If the answer is zero, the hose fitting will fall to the floor after moving a couple of inches. If the answer is "a lot", that coupling can launch itself at least halfway thru an inspector, traveling at a large fraction of the speed of sound.

 

[mech5]

All the air in the system is suppose to be bled out before testing begins. There's been a few instances where the coupling has been ejected and hit the side of the testing chamber and dented the 3 inch steel plate.

 

[1gibson]

If everything you put into the simulation is exactly as it is supposed to be, that's going to be a very boring simulation.

 

[LittleInch]

If you know the pressure in the hose and the size of the coupling, you have a force. Just assume this force lasts for 1,2 or 3 seconds and work out the acceleration from F = Mass x acceleration and then you can find your velocity.

I'm struggling to work out why you're working this out though....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[mech5]

I'm checking to see if the test chamber is adequate in case of possible failure.

 

[Duwe6]

"There's been a few instances where the coupling has been ejected and hit the side of the testing chamber and dented the 3 inch steel plate."

Instead of building a tougher chamber, get a competent test operator. It is simple to tell how much air is in the system; "How long did the pump run". Bet the answer for your catastrophic test was "Oh, about a minute or 3."

Other alternative to finding a competent test person is to have them use a hand pump. Now leaving air in the vessel causes them to work harder and longer. They will work diligently to evacuate ALL the air prior to pumping up to hydro pressure.

 

[Timelord]

How much hose is in the system and how elastic is it? This could be the problem?

Timelord

 

[Compositepro]

"How much air was left in the system when the hydro pump was started? If the answer is zero, the hose fitting will fall to the floor after moving a couple of inches."
That is not really true. Depending on the pressure, there can be significant energy stored in the the elastic expansion of a pressure vessel and the compression of a liquid. Worst case is that the object is propelled by by the test pressure. The pressure driving the projectile will have dropped very significantly by the time it has moved by one hole diameter (think, does a bullet accelerate after it leaves the muzzle?). The projectile will have moved one hole diameter in a small fraction of a second.

 

[MikeHalloran]

If a flying test article dented a piece of steel plate that's three inches thick, you probably should relocate the test apparatus to the bottom of a deep quarry, and operate it remotely. ... e.g., from two states away.





Mike Halloran
Pembroke Pines, FL, USA

 

[AWloo]

Without knowing what your test setup is I would try changing the testing procedure to prevent this from happening in the first place. A proactive approach beats a reactive approach. That being said, you may also want to look into hose swing checks, which can prevent the whiplashing of a hose in a failure condition.

Best regards,
AWloo

 

[moon161]

Speed of the hose would be the < the speed of the free jet at the given pressure. Is that Deltap/rho?