good day,

Anyone can explain the theory/formula which causing pressure drop during perform hydrostatic test in raining day?
The situation is for heat exchanger tube side hydrotest.
i believe it is cause by heat transfer (temperature difference between fluid inside tube and ambient temperature). How to relate heat transfer with pressure or temperature with pressure?

thank you.

You can predict in principle not in quantity. Water expands (little but it does) increasing temperature and the contrary. Sometimes the item is left to the sun and the pressure raises remarkably quick, but it depends on the size of the item and the thickness.
Regards.
mauro

Thanks for the comment.

so your point is the contract of water (during raining day) causing the pressure drop right? i believe you are talking about relationship between volume and pressure. Are you mind to mention the name of the principle apply?

how about the tube? the tube dint contract at the same time water contract?

thank you.

so your point is the contract of water (during raining day) causing the pressure drop right? i believe you are talking about relationship between volume and pressure. Are you mind to mention the name of the principle apply?
how about the tube? the tube dint contract at the same time water contract?
thank you.[/quote]

You mean the pressure vessel itself, I presume.
Yes it shinks and expands as the water do, but the volume of the water contained is much more than the volume of the steel of the pressure vessel. That's why the behaviour of water prevails.
Mauro

You mean the pressure vessel itself, I presume.
Yes it shinks and expands as the water do, but the volume of the water contained is much more than the volume of the steel of the pressure vessel. That's why the behaviour of water prevails.
Mauro[/quote]

The principle is in the first equation of thermodinamics: pv=RT
Mauro

Dear GOnzaga,

a little bit confusing here, if not mistaken pv=rt is gas equation....is it applicable for water?

thanks.

The principle is in the first equation of thermodinamics: pv=RT
Mauro[/quote]

Yes it is the gas equation, but i believe you may start from this. Water expands with heat as well. You may also consider that heat and pressure are form of energy and there is alway a balance. But this is a forum on Sect.VIII Div.1. Sorry I studied these problems half a century ago Now it is your time to study.
Mauro

In my opinion, i think the density of water play an important role.

The density of a fluid changes with temperature and pressure. The density of water versus temperature and pressure is indicated in the chart below:



Suppose we perform hydrotest at ambient temperature 20 degree C. we pressure up the water by compress the water (since the volume water (follow volume vessel) is constant, we are actually introduce more mass into constant volume), this actually increase the density (kg/m3) of water which consequently increase the pressure. Read vertical up from 20 degree C.

During holding pressure (suppose 25 Bar), there is no more water force into vessel, which means the density is constant now. when raining day, the ambient temperature drop. Since the density is constant (more water force into vessel), read horizontal at 25 Bar, the temperature drop will cause the pressure drop.

hopefully above explanation make sense. Please correct me if there is mistake.

Thank you.

Yes,i think it shinks and expands as the water do, but the volume of the water contained is much more than the volume of the steel of the pressure vessel. That's why the behaviour of water prevails,and the density of water play an important role.

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Here I am posting a attachment formula by this time graph is not with me till that you can refer API 1104 for this

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