Hydrostatic test of pressure vessel

[lcatg]

Hi,
w.r.t the attached image explaining Hydrostatic test process (link

http://www.inspection-for-industry.com/vessel-pressure-testing.html

) its given that pressure is increased in stages. since the water (if used as test liquid) is incompressible how is it possible to increase to the desired pressure? once the vessel is filled fully, the pressure varies from 0 at top to P=rho*g*h at the bottom. How is it possible to raise the pressure?

 

[LittleInch]

Water is "virtually" incompressible, but not exactly 100%.

Similarly your vessel is not a truly solid object, but expands under pressure / stress.

So the amount of water required to raise pressure from 0 at the top to your test pressure might be very small, but then so is your pressurising pump / piston.

This FAQ is about thermal expansion, but the principle is the same - increase in volume versus increase in pressure

http://www.eng-tips.com/faqs.cfm?fid=1339

It's probably somewhere between 1 x 10-4 and 1 x 10-3 in terms of volume to get to your test pressure - small but finite and measurable.

A lot depends on the volume of your pressure vessel relative tot he volume of your pressusiing pump / piston


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[lcatg]

LittleInch,

How did that 4th formula increase in volume due to increase in pressure come? please find the attached file showing different formula.

 

[LittleInch]

Don't know - I didn't write it. My point was not to generate an equation, but answer your rather simplistic question and point out that nothing is really incompressible, nor is the vessel itself an immovable object - does expand under pressure.

If you're trying to find volume of water required to raise the pressure in the vessel by a certain pressure then you also need to include the Bulk Modulus of water - 2.3 x 10^9 Pa



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.