Design temperature downstream of coolers?

[Jafka]

I've always set the design temperature of piping and equipment downstream of a cooler is based on the normal operating temperature upstream of said cooler.

e.g. Cooler E-201 reduces the temperature of a gas from 200F to 80F. All downstream piping should be designed for 200F + a design factor.

Does anyone know if there's a source of this practice that I can reference? (design guidelines, ASME, company standards, etc).

Thanks!

 

[chemebabak]

There are no official standards for process design criteria. Each company has their own engineering guidelines for design processes. There are some companies that place their design criteria online:

http://217.174.18.60/ips/pr/e-pr-850.pdf

http://217.174.18.60/ips/pr/e-pr-880.pdf

http://www.standard.no/en/Sectors/Petroleum/NORSOK-Standard-Categories/P-Process/

http://www.gulleyassociates.com/engineeringtips.html

There is one that sells it:

http://kolmetz.com/guidelines.html

You could probably find a lot more.

In this specific instance you need to use good judgment. Are you designing the pipe for 200°F because there may be a loss of cooling water from the tower? That seems reasonable. What if it is an air cooler that loses its fans? In that case you can take credit for heat lost to atmosphere by convection.

There are no rules or laws for making these design decisions. Is the design margin 5% or 25%? This is all based on engineering judgment. Even the design standards are based on some engineers judgment. You could probably put 10 engineers in one room and get 11 different opinions on how to design a process. On top of that, a lot of these design criteria are copied from other companies. Some engineers in company A use 10% design margin. Then they transfer to company B and say, "Well, let us use 10% because that is what we used in company A." But they don't know that 10% is right or wrong, and now all of company B uses 10%. Back when I was a junior engineer fresh from college I asked the "experienced" guys why is it 10%, or why do we put the X downstream of the Y. There answer was, "Well, that is what we did on the last job."

Hey, just keep asking those types of questions and you should be able to come up with your own design criteria.

 

[SNORGY]

To me, the design temperature downstream of the cooler is the same as the design inlet temperature, less whatever adjustments you want to make for free convection to atmosphere in still air on a hot summer day with no fans running.


Regards,

SNORGY.

 

[MortenA]

If you refer to API 14C/ISO 10418, then you can add a high temperature shut down alarm and set the design temperature at this value, including a margin. However, care should be taken not to define higher design temperature than required when it affects the selection of material and pressure class rating.

Best regrads

Morten