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Trv Or Psv For A Fuel Transloading System?


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#1 Reckless73

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Posted 27 January 2021 - 12:12 PM

Hello,

I'm the project engineer of a fuel (gasoline and diesel) transloading system, to which relief valves should be included in the design. The valves will be located on a 6" pipe, which collects fuel from tank cars (cars at atmospheric pressure). The fuel is pumped to tank trucks, and the released vapor is sent back to the tank cars.

 

I'm kindly asking for your recommendations, by choosing a TRV or a PSV valve.

I already performed the TRV calculation, by setting pressure at 18 psi_g, according to process conditions.  Set pressure was calculated by fluid hydrostatic pressure plus vapor pressure at normal boiling point. Volumetric relief flow was calculated from API 521 Addendum.

On the other hand, if PSV is chosen, its design must be carried out to address fire case (liquid vaporization). However, API 521 correlations are intended to vessels rather than pipes; in particular, because wetted area is needed. Could I use the correlations anyway?

 

Finally, either for TRV or PSV, I have some doubts on choosing set pressure. Is API 576 applicable to determine set pressure?

I'm aware that I posed several technical issues. I would really appreciate your help.

Regards.



#2 latexman

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Posted 27 January 2021 - 03:24 PM

What does your acronym "TRV" stand for?  I can think of two reasonable meanings, maybe there is more.  So, I'd like to know the one you are referring to?



#3 fallah

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Posted 28 January 2021 - 01:19 AM

Hello,

I'm the project engineer of a fuel (gasoline and diesel) transloading system, to which relief valves should be included in the design. The valves will be located on a 6" pipe, which collects fuel from tank cars (cars at atmospheric pressure). The fuel is pumped to tank trucks, and the released vapor is sent back to the tank cars.

 

I'm kindly asking for your recommendations, by choosing a TRV or a PSV valve.

I already performed the TRV calculation, by setting pressure at 18 psi_g, according to process conditions.  Set pressure was calculated by fluid hydrostatic pressure plus vapor pressure at normal boiling point. Volumetric relief flow was calculated from API 521 Addendum.

On the other hand, if PSV is chosen, its design must be carried out to address fire case (liquid vaporization). However, API 521 correlations are intended to vessels rather than pipes; in particular, because wetted area is needed. Could I use the correlations anyway?

 

Finally, either for TRV or PSV, I have some doubts on choosing set pressure. Is API 576 applicable to determine set pressure?

I'm aware that I posed several technical issues. I would really appreciate your help.

Regards.

 

Hi,

 

To get a proper and helpful response, please upload a simple sketch of the system you described...



#4 Reckless73

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Posted 28 January 2021 - 08:52 PM

What does your acronym "TRV" stand for?  I can think of two reasonable meanings, maybe there is more.  So, I'd like to know the one you are referring to?

TRV: Thermal Relief Valve



#5 Reckless73

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Posted 28 January 2021 - 08:58 PM

 

Hello,
I'm the project engineer of a fuel (gasoline and diesel) transloading system, to which relief valves should be included in the design. The valves will be located on a 6" pipe, which collects fuel from tank cars (cars at atmospheric pressure). The fuel is pumped to tank trucks, and the released vapor is sent back to the tank cars.
 
I'm kindly asking for your recommendations, by choosing a TRV or a PSV valve.
I already performed the TRV calculation, by setting pressure at 18 psi_g, according to process conditions.  Set pressure was calculated by fluid hydrostatic pressure plus vapor pressure at normal boiling point. Volumetric relief flow was calculated from API 521 Addendum.
On the other hand, if PSV is chosen, its design must be carried out to address fire case (liquid vaporization). However, API 521 correlations are intended to vessels rather than pipes; in particular, because wetted area is needed. Could I use the correlations anyway?
 
Finally, either for TRV or PSV, I have some doubts on choosing set pressure. Is API 576 applicable to determine set pressure?
I'm aware that I posed several technical issues. I would really appreciate your help.
Regards.

 
Hi,
 
To get a proper and helpful response, please upload a simple sketch of the system you described...

Mr Fallah,

I send you the sketch.

Thanks!

Attached Files



#6 latexman

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Posted 28 January 2021 - 09:57 PM

I would go with TRV, but 18 psig set pressure seems way too low to me. What is the pressure rating of the 2” and 6” pipe per your pipe specs? What pressure were they hydro tested to? I’d consider making the TRV set pressure equal to the 6” pipe pressure rating, or a nominal 150 psig.

#7 breizh

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Posted 28 January 2021 - 10:26 PM

Hi,

Consider the post attached , other information are available using the search engine in this forum.

 

https://www.cheresou...l-relief-valve/

 

For TRV sizing , refer to Leser  document , page 7- 4 -10-9 

 

Hope this is helping you.

Breizh 


Edited by breizh, 28 January 2021 - 10:40 PM.


#8 fallah

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Posted 29 January 2021 - 02:20 AM

Hello,

I'm the project engineer of a fuel (gasoline and diesel) transloading system, to which relief valves should be included in the design. The valves will be located on a 6" pipe, which collects fuel from tank cars (cars at atmospheric pressure). The fuel is pumped to tank trucks, and the released vapor is sent back to the tank cars.

 

I'm kindly asking for your recommendations, by choosing a TRV or a PSV valve.

I already performed the TRV calculation, by setting pressure at 18 psi_g, according to process conditions.  Set pressure was calculated by fluid hydrostatic pressure plus vapor pressure at normal boiling point. Volumetric relief flow was calculated from API 521 Addendum.

On the other hand, if PSV is chosen, its design must be carried out to address fire case (liquid vaporization). However, API 521 correlations are intended to vessels rather than pipes; in particular, because wetted area is needed. Could I use the correlations anyway?

 

Finally, either for TRV or PSV, I have some doubts on choosing set pressure. Is API 576 applicable to determine set pressure?

I'm aware that I posed several technical issues. I would really appreciate your help.

Regards.

 

Hi,

 

It certainly is TRV for pressure relief of trapped liquid which is subject to thermal expansion due to, say, sunshine; but as Latexman mentioned it's strange considering such low set pressure for it...



#9 Reckless73

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Posted 02 February 2021 - 06:45 AM

Hello,

Thanks for the guidance.

The fluids are gasoline and diesel, now I'm considering 150 psi, the rating for this pipe. The operation temperature is 68°F and the relief temperature will be 100°F. The gasoline has a vapor pressure at the relief temperature about 7 psi_g, and for the diesel is almost zero, respectively. 

My concern, is it sufficient with a thermal expansion or I need another scenario?

 

Regards



#10 fallah

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Posted 02 February 2021 - 06:58 AM

 

Thanks for the guidance.

The fluids are gasoline and diesel, now I'm considering 150 psi, the rating for this pipe. The operation temperature is 68°F and the relief temperature will be 100°F. The gasoline has a vapor pressure at the relief temperature about 7 psi_g, and for the diesel is almost zero, respectively. 

My concern, is it sufficient with a thermal expansion or I need another scenario?

 

 

Hi,

 

Please recheck the set pressure of the TRVs; it might be 18 barg rather than to be 18psig.

It seems the only scenario for over pressure of the piping on which the TRVs are installed; is thermal expansion...



#11 breizh

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Posted 02 February 2021 - 07:11 AM

Hi,

In some part of the world the outside temperature could be as high as 40 to 45 C  in summer . 

To be considered for the TRV sizing (expansion) .

Good Luck

Breizh 



#12 latexman

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Posted 02 February 2021 - 09:53 AM

Your company policies and past practices are your best guide.  Like Fallah, I think your two thermal relief valves are fine.  My company does not protect piping from fire with PSVs.  There is no Code requirement.

 

If the liquid gets blocked in/trapped at 68o F, the TRV could activate after the liquid is warmed up only 1-3o F more.  If the liquid gets blocked in/trapped at 100o F, again, the TRV could activate after the liquid is warmed up only 1-3o F more.  Take a look at a small write-up I did on another website.  TRV's have pressure set points, not temperature set points.  A TRV set pressure of 150 psig is reasonable in your case if the pipe is a 150 psig design..



#13 Reckless73

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Posted 03 February 2021 - 07:39 PM

I'll trying to explain more about this. I am apologized that it's too long.

 

The valves are already installed, they are working but they have significant leaks. The plant manager reports that at the end of the transfer operation, the valves continuously vent. They measured the pressure of the trapped liquid and it is between 85 - 95 psi_g, the ambient temperature is currently 22 ° C (71.6 ° F) and can go up to 49 ° C (120 ° F).
 
I checked in API 520, part II, section 4.4 that to mitigate leaks the set pressure must be increased. Which, has already been discussed and I proposed a 150 psi pressure but a robust foundation is required to make such a change, since it is not enough with what I have proposed.
So, I have to calculate what the pressure of the trapped liquid would be in the event that it reaches 120 ° F. I performed the calculation with the thermal expansion scenario and how well you know the values ​​that these calculations give are greater than what the pipe would withstand above 3000 psi for the change in temperature that would occur, which would give me approximately 97 psi / ° F.
 
Is there another way to calculate the pressure of a trapped liquid? Since gasoline has a boiling temperature between 80 ° F and 437 ° F, the comment is that the generated vapor is possibly causing the overpressure.
 
Regards.





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