Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

2

Pressure Rise Calculation Due To Simultaneous Heating Of The Pipe And


4 replies to this topic
Share this topic:
| More

#1 crispe07

crispe07

    Brand New Member

  • Members
  • 2 posts

Posted 26 March 2018 - 05:18 AM

Hi,
I am working in a project where there is a pipeline filled with water and traces of glycol at 50ºC. That pipeline can be blocked and the client suggests a thermal relief valve. I am trying to justify if this thermal relief valve is needed or not.
As per API 521 (6th edition, 2014) section 4.4.12.4:
Where the system under consideration for thermal relief consists of piping only (does not contain pressure vessels or heat exchangers), a PRD might not be required to protect piping from thermal expansion if any of the following apply:
 c) The fluid temperature is greater than the maximum temperature expected from solar heating [usually approximately 60 °C to 70 °C (approximately 140 °F to 160 °F)] and there are no other heat sources such as heat tracing (note that fire is generally not considered when evaluating pressure-relief requirements for piping);
If we consider 70º as the maximum temperature expected from solar heating (our pipeline is not in the upper part of the rack, but we cannot say which is the maximum T expected), we can't consider this point as our case. 
d) The estimated pressure rise from thermal expansion is within the design limits of the equipment or piping.
I used the equation (3) from API 521 (6th edition, 2014) section 4.4.12.4 for pressure rise due to simultaneous heating of the pipe and blocked-in liquid and I am getting a pressure rise of 49 kg/cm2 by the increase of 1ºC of temperature.
I also calculate the temperature rise due to solar radiation (taking 1.04kW/m2 for intensity of solar radiation in accordance with API 521) and I am getting a temperature rise of 5ºC, resulting in a pressure increase of 245 kg/cm2 based on the results of pressure increase I mention previously.
This does not make much sense so I am wondering if this is correct.
Does anyone have any thoughts?
 



#2 fallah

fallah

    Gold Member

  • ChE Plus Subscriber
  • 4,507 posts

Posted 26 March 2018 - 06:00 AM

Hi,

 

Why it doesn't much sense to you?

 

For every one degree of centigrade rise in temperature for a liquid water in a sealed pipe segment pressure would go up around 4-5 bar, hence your calculation result couldn't be wrong.

 

You should consider design pressure of the pipe segment and apply a TRV if the pressure rise due to thermal expansion is higher than the design pressure.



#3 Pilesar

Pilesar

    Gold Member

  • Members
  • 485 posts

Posted 26 March 2018 - 10:14 AM

Thermal relief valves are cheap. Broken piping is expensive. Engineers should not always trust their own imagination to find every possible reasonable scenario which could cause problems. Most thermal relief valves never operate, but that does not mean they should not have been installed. I know of real problems that occurred because calculations showed a thermal relief was not needed so one was not installed. If I suspect a thermal relief might be needed or seriously questioned, I add the thermal relief and move on to the next part of the project.

  In your particular case, I see your argument and it is certainly possible a thermal relief is not needed. I would still install one since the client wants it. Clients can cause you a lot of trouble and it is good practice to let them find small 'errors' to correct. Adding a thermal will not cost the project much and may help the relationship with the client. Who knows whether you have a large error somewhere else and need the client's cooperation to negotiate a reasonable solution. 

  Your water line will not always be at 50C. Some times it will be at ambient while the plant is down. The thermal relief will protect the piping in that scenario.


Edited by Pilesar, 26 March 2018 - 10:16 AM.


#4 crispe07

crispe07

    Brand New Member

  • Members
  • 2 posts

Posted 27 March 2018 - 01:13 AM

Thank you all for your answers smile.gif. We finally decided to install de PSV.
One more question: Would it be the same conclusion if the fluid was only water (with no traces of glycol)? Other important information is that the lenght of the pipe is about 250m.


Edited by crispe07, 03 April 2018 - 08:02 AM.


#5 fallah

fallah

    Gold Member

  • ChE Plus Subscriber
  • 4,507 posts

Posted 05 April 2018 - 01:13 AM

Thank you all for your answers smile.gif. We finally decided to install de PSV.
One more question: Would it be the same conclusion if the fluid was only water (with no traces of glycol)? Other important information is that the lenght of the pipe is about 250m.

 

Yes, it would lead to the same conclusion and being or not being the traces of glycol has no considerable effect...






Similar Topics