SurfLung wrote: ↑Thu Jan 03, 2019 2:38 pm
Thanks fellows... That's a lot of great information. I agree its not a good idea to try this but it has turned into a fascinating topic to discuss. I thought I was asking a fairly simple question but it looks like its a lot more complicated than I thought. So, I'm still unclear on a few things.
First, the in-compressible nature of water. I was under the impression that the reason they fill a test tank with water instead of air is because if the tank fails physically (cracks open), the "explosion" will only amount to the expansion of the water inside, which is minimal due to the incompressible water... So the test tank might just crack open and stop. Is this a correct assumption?
Second, if placing the water filled test tank in open water would enhance the explosion because of the in-compressibility of water, what if you just did it in open air?
Third, If an air tank and high pressure hose were used to raise the internal water pressure in the test tank, why would they have any contribution to an explosive failure of the test tank? It seems to me that the test tank would crack open and the air tank and hose would simply free flow until you turn the valve off.
First question is mostly correct.
But here are a few clarifications:
The amount of energy stored in the compressibility of the water can be considered truly negligible. The compression and therefore re-expansion of the water at these pressures can be basically ignored.
The elasticity of the steel cylinder in itself does store some elastic energy due to the expansion. The same applies to hoses, but their diameters is very small therefore the stored elastic energy is small.
The air in any gauges (or any trapped air that was not totally bled) will store some energy.
The video shows the inertia generated by the stored energy (in the elastic steel and other elastic materials).
Second question.
As you can see on the video that is the preferred media if you are going to intentionally take a cylinder to a rupture condition.
The only reason the hydro test is done inside a water jacket is to use the water on the outside of the jacket to measure the volumetric expansion. This method is used to amplify a very small cylinder expansion into a burette that can be read with reasonable accuracy.
This is the most economical and accurate way of amplifying a deflection that would be very hard to measure directly. But the total volume expansion of the cylinder can be measured because the displaced water is concentrated into a relatively small burette.
BTW, the water jacket (container) around the cylinder has a large blow disc that is always installed pointing away from any personnel in the area. The blow out disc is about 7 or 8 inches in diameter. I have done many hydro tests, but I have never actually being present during a rupture. I have seen the results shortly after and it is just a mess, but no harm occurred (other than a new disc has to be installed). Well I don’t know about the clothing of the operator at the time.
Question three.
If you can close the valve in milliseconds you may be OK, but even then, probably not.
Take a look at the motion on the cylinder in the video. You heard a water pump and there was minimal amount of stored energy in the entire system.
The energy stored in the attached cylinder will released and accelerate all the water like liquid projectiles until the valve is closed. That water will hit like a pressure washer cleaner but a lot more volume at once. It could cut right through flesh like a hot butter knife on butter.
At the same time (for every action there is an equal and opposite reaction) the cylinder will be propelled in the opposite direction.
A human would have a hard time closing that valve fast enough to minimize the reactions. You could try barely opening it and maybe even putting a restrictor orifice. But there is too much risk of adding too much compressible (energy storing) air into the system.
I think you mentioned about having a high pressure "bicycle style" pump. That could be safer (due to lower air volume) if you have a hose long enough to get far away. But make sure to fill the hose with water and maybe even add a restrictor orifice in a joint near the cylinder.
Restrictor orifices are commonly used to slow the flow of compressed oxygen when transfilling, and most modern Scuba HP gauge hoses have them on the fitting at the regulator end (look t the end of the 7/16" fitting).
Added:
I should add that because of the sudden nature of the rupture. The abrupt energy release creates a shock or energy pulse. Even a relatively small amount of energy when released suddenly in a pulse can cause some damage due to the sudden acceleration of any mass involved (the water or the cylinder).
I have been thinking about making a clear pressure chamber to test gauges and dive computer. I am thinking about using a clear water filter container. They are rated to city water pressure . To avoid the danger of elastic energy (from compressed air) I would have to evacuate all the air out of it and I would use a bicycle pump to pressurize it. I have thought about connecting it using an HP hose with its built in restrictor orifice.