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Topic: Is LPG considered incompressible?  (Read 4873 times)

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Offline chen4

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Is LPG considered incompressible?
« on: December 10, 2013, 09:24:01 AM »
Can LPG be considered as incompressible? and a relief valve be used for LPG bullets?

API 521 states that a relief valve is normally used with incompressible fluids.
Is it like..When petroleum gas becomes LPG, it is already compressed to the maximum and is not compressible anymore...hence LPG is considered incompressible and a relief valve is used for protecting LPG bullets???

Thanks in advance for the help.

Offline poppinjoshi

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Re: Is LPG considered incompressible?
« Reply #1 on: December 15, 2013, 05:02:13 AM »
Yeah....LPG is being considered as alternate to water for hydraulic fracturing of hydrocarbon formations. Only incompressible fluids can be used for such an operation.
In reality incompressibility is an approximation, it just means that a fluid is not showing any significant change in volume with change in pressure.
All matter is compressible, remember that sound waves travel through water as longitudinal waves, which requires compressive action; sound can travel through walls. In fact such waves exist only where there is matter.

Offline chen4

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Re: Is LPG considered incompressible?
« Reply #2 on: December 23, 2013, 08:17:28 AM »
Thankyou very much poppinjoshi :) It did help a lot.

Offline curiouscat

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Re: Is LPG considered incompressible?
« Reply #3 on: January 23, 2014, 11:06:41 AM »
Can LPG be considered as incompressible? and a relief valve be used for LPG bullets?

No I doubt that. As soon as you drop Pressure it will flash into a two phase flow. You cannot use a valve rated for Liq. duty only.

Offline bangzone

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Re: Is LPG considered incompressible?
« Reply #4 on: January 24, 2014, 03:15:18 AM »
According to API 521,
generally we call it 'relief valve' for incompressible fluids, while 'safety valve' for compressible.
So, you need 'relief valve' or 'safety valve' no matter if fluid is incomprssible or compressible.
If i am wrong, please comment.
 

Offline curiouscat

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Re: Is LPG considered incompressible?
« Reply #5 on: January 24, 2014, 06:10:50 AM »
According to API 521,
generally we call it 'relief valve' for incompressible fluids, while 'safety valve' for compressible.
So, you need 'relief valve' or 'safety valve' no matter if fluid is incomprssible or compressible.

Right. But he cannot be using a 'relief valve' where a 'safety valve' is needed. Former is for Liquids & latter for gases.


Nitishajack

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Re: Is LPG considered incompressible?
« Reply #6 on: April 18, 2014, 11:45:11 AM »
Yes, you consider it a liquid if you are sizing a thermal relief valve. However, a regular PSV sized for fire case will be sized on vapor or supercritical service, as that is what will be relieved as the LPG heats up.

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