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Pressure Generated By Heated Pipeline Liquid

over pressure hydraulic expansion

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#1 vaibhav

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Posted 23 March 2019 - 12:31 AM

Dear Members.

 

I am working on jet fuel piping project ( Location is Middle east ) .

 

Client ask me to calculate the pressure increase due to thermal expansion of the blocked inventory .

 Piping design pressure and design pressure of the thermal relief valve is 65 bar g. piping op. pressure is 45 bar g & op temperature is ambient. temperature of the liquid in stand still condition during summer is 50 Deg C.

 

My question is it really required to do the calculations for pressure rise ?

 

I  had already calculated rate of thermal relief valve through the valve . pl. refer  attached calculation sheet.

 

 If to calculate the pressure rise ,  need to know the initial gauge pressure of the blockade liquid in the pipeline.

 

awaiting for the valuable advice from the  community members.

 

Regards

Vaibhav

 

 

 

 

Attached Files



#2 Dazzler

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Posted 23 March 2019 - 12:55 AM

Hi Viabhav,

 

I have looked briefly at the calculation. It seems to have a known standard as basis and reasonable assumptions.

 

For a "compressible fluid" such as a gas then it could be sensible to calculate the pressure rise to see if a relief valve is needed for such a scenario.

 

For a ''non-compressible fluid" such as a liquid, it makes no sence to calculate as the pressure rise if the pipe is short, as the pressure will "sky rocket" well above any pipe operating or design pressure unless you let a few drops out via relief.  For a longer pipeline it might make sence so long as you are also calculating the thermal expansion of the metal pipe as well as that of the liquid within.  They may counteract each other. It could  be that the metal pipe heats and expands more than the liquid within.  I don't know.  It is probably unlikely and so not routinely done.  You could check the thermal expansion coefficients for the liquid and the metal to see how they differ.

You could also look for what a pipeline design code states, rather than the relief valves code.

 

Dazzler


Edited by Dazzler, 23 March 2019 - 12:55 AM.


#3 Chemitofreak

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Posted 25 March 2019 - 03:03 AM

There are two things while doing calculations for Thermal Relief Valve:

 

1) Where the flow rate is low (e.g the pipe length is short and contains a liquid of low volatility) the accumulated pressure is not important because the relief valves will pass the liquid before any pressure accumulates. Only the set pressure of the valves and any constant back pressure needs to be considered.

 

2) When thermal relief valves are installed on short lengths of pipes with less volatile liquids and the pipe is not heated, the flow rate through the valve may be ignored, as it will be trivial and any standard orifice will be large enough to handle the capacity. Hence, size 'D' is mostly used



#4 latexman

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Posted 25 March 2019 - 06:09 AM

To get an idea of the pressure developed on heating a packed liquid you may divide the absolute values of the cubic thermal expansion of the fluid

 

α = (1/ V)(∂ V/∂T)p

 

by its isothermal compressibility

 

κ = -(1/ V) (∂ V/∂ p)T

 

for the envisioned temperature range.  This results in pressure units/temperature units, like bar/oC.  For every oC temperature rise you get the bar pressure rise in the pipe.  It's a very handy property to know.

 

α and κ can be estimated from physical properties; α from the density changes, and κ from the Mach number in the liquid.  I’ll leave it to you to find jet fuel physical properties.  I never deal with it in my work.


Edited by latexman, 25 March 2019 - 06:14 AM.


#5 breizh

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Posted 25 March 2019 - 07:22 AM

hi ,

For those interested with the subject , a detailed explanation and calculation in this old paper issued in 2001 (Chemical engineering magazine) .

 

Hope this is going to give you some light. Don't underestimate the risk and consequences . 

good luck

Breizh 

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#6 vaibhav

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Posted 16 April 2019 - 05:36 AM

Dear Team Members

 

Client is still insisting to submit calculation for the pressure rise in the piping due to thermal expansion of the liquid. piping design code is ASME B 31.3 AND design pressure is  65 bar g. product is Jet fuel use for aviation purpose ( aircraft engines ) .

 

please find attached one of the sample calculation I did for  pressure rise in the piping due to thermal expansion of the liquid in between to blocked valves.

there will be tremendous increase in the pressure values for every one degree centigrade temperature change. piping design pressure is 65 bar g and TSV set pressure is same as that of that of the piping design pressure. 

 

basis the attached calculation, it seems that pressure rise will be over the design pressure of the piping system which calls for additional Pressure safety valve in addition to TRV on the piping ? please correct me if I am thinking in wrong direction.

 

Your comments on this technical issue/ submitted calculation will be very helpful to me.

 

Regards

Vaibhav

 

 

 

Attached Files



#7 latexman

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Posted 16 April 2019 - 08:40 AM

 

 

it seems that pressure rise will be over the design pressure of the piping system which calls for additional Pressure safety valve in addition to TRV on the piping ?

 

That's why the thermal relief valve (TRV) is there.  Set pressure is usually the piping design pressure.  TRV's usually have to relieve a small volume/volumetric flow of fluid.  A 1/2" to 1" TRV (whatever the minimum size is) is usually oversized,  No need for two relief valves.  10 m of 200 mm pipe is not overly big or long, so no concern.  The attached calculation looks good.


Edited by latexman, 16 April 2019 - 09:01 AM.


#8 breizh

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Posted 16 April 2019 - 10:35 AM

Hi,

I got similar result solving equation 38 of the document submitted in my previous post based on the data provided  ; 10.7 bars/ 1 C

 

Breizh



#9 vaibhav

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Posted 17 April 2019 - 11:32 PM

Dear members:

 

Thanks for your replies.

 

But still, a concern remains: - if hydraulic pressure generated in the pipeline due to thermal expansion of the liquid is exceeding the design pressure of the piping, then it will result in the pipeline bursting or a failure of the weakest component ( flange leakage, gasket failure, etc.).  Therefore, how do we prevent it?

 

Calculation results shows that there will be tremendous increase in the pressure even for a one degree rise in temperature.  Is a burp of the liquid relieved through the TRV at set pressure enough to bring down the pressure so there is no threat to the integrity of the pipeline?

 

Please advice.

 

Regards

vaibhav



#10 breizh

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Posted 18 April 2019 - 01:52 AM

hi ,

you need to assess what is the weakest point of your system and set the TRV to prevent it . Is it the pipe, the flanges , the gaskets .

 

Note : I got once an issue because tracing was not taking account on a phenol pipeline , freezing was understood , not stagnant liquid during shut down .

 

Good luck

Breizh



#11 latexman

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Posted 18 April 2019 - 06:21 AM

 

 

burp of the liquid relieved through TRV at set pressure is enough to bring down the pressure so no threat to the integrity of the pipeline ?

 

That is correct.  Relieve a few ml and the pressure is reduced significantly.  By API 521, it is RAGAGEP to do no calculations and put a nominal 3/4" x 1" PSV to protect a pipe in the process area.  If the pipe is large in diameter and/or length (i.e. a pipeline), calculations should be done.

 

 

4.4.12.2 Sizing and Set Pressure

The required relieving rate is not easy to determine. Since every application is for a relieving liquid, the required
relieving rate is small; specifying an oversized device is, therefore, reasonable. A nominal diameter (DN) 20 × DN 25
(NPS 3/4 × NPS 1) relief valve is commonly used. If there is reason to believe that this size is not adequate, the
procedure in 4.4.12.3 can be applied. If the liquid being relieved is expected to flash or form solids while it passes
through the relieving device, the procedure in 4.9.2 is recommended.
Proper selection of the set pressure for these relieving devices should include a study of the design rating of all items
included in the blocked-in system. The thermal-relief pressure setting should never be above the maximum pressure
permitted by the weakest component in the system being protected. However, the PRD should be set high enough to
open only under hydraulic expansion conditions. If thermal-relief valves discharge into a closed system, the effects of
backpressure should be considered.





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