Design Pressure and Temperature 1

[Riko_93]

Could you please tell me what are the differences between the following terms?
Upper operating pressure/temperature
Lower operating pressure/temperature
normal pressure/temperature and operating pressure/temperature

Thanks in advance

 

[LittleInch]

Riko,

you're asking some pretty basic questions here without any explanation of your role, location, support network, etc. Please provide a bit of background.

All these mean are gradually increasing number from low, medium and high and all the parameters can vary within those bounds without causing an issue.





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[Riko_93]

These are for separator design. I forgot to write. I'm confusing to decide these parameters. For example, the operating pressure of separator is 50 barg. Design pressure is 60 barg. I have read a lot about these terms. But, don't understand how to decide these parameters.
Flow comes from some land wells. Gas = 10 MMscfd. CGR = 10 bbl/MMscf condensate, no water is produced. Arrival T = 5 to 30°C.
Gas is 2% CO2, 90% C1, 1% C2, 2% C3, 2% iC4, balance C5+
Condensate: density 700 kg/m3
FTHP = 50 barg
CITHP = 120 barg

 

[LittleInch]

ok, from the top.

Design pressure for a pressure vessel should be the pressure never exceed. (actually pressure vessel really should have a MAWP calculated which might be higher, but same thing - it's a maximum pressure at a certain temperature which cannot be exceeded - no additional margin is allowed.

Pressure alarms, trips and relief settings normally need a margin below DP or MAWP, hence your upper operating pressure/temp where operation is possible before the units alarm and trip.

normal is what you expect the majority of the time

Lower is the lower end of "normal" and for a separator might result in high velocities and poor operation




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Also: If you get a response it's polite to respond to it.

 

[Riko_93]

First of all, thanks for the explanation.
If I have the max/normal/min operating pressure, then why I need to calculate also design max/min pressure or temperature? What is difference between max/min operating P/T and max/min design P/T ?

 

[Latexman]

Because you may want to steam a vessel out or solvent wash it at 150^oC. Likewise, if you steam out a vessel, it should be designed for full vacuum, in case the steam inside condenses suddenly, like it may do during a cold rain outside or if the fire water sprinklers activate by accident inside. You have to ask yourself, what can happen? Then, design for it so you don't risk the vessel's integrity.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[Riko_93]

Thanks. I got the point. I'm grateful to you for your help

 

[MJCronin]

Littleinch,

The ASME B&PV Code Section VIII, requires a certified relief device (or devices)for every Code vessel.

The setting of that device shall be not greater than the MAWP for the vessel. In practice, unless there is a good reason for a lower pressure setting, the MAWP is most often used

http://www.nationalboard.org/index.aspx?pageID=134&ID=287

This does not prevent the use of devices on the system set at lower pressure to facilitate process control

MJCronin
Sr. Process Engineer

 

[LittleInch]

MJC

I know that, my point above was that if you set the RV at the MAWP, then the maximum or upper operating pressure needs to allow for the accuracy of the relief valve (sometimes 10%) set point and setting of high and high high pressure alarms and trips.

Hence for a vessel with a MAWP of 10 barg, it is unlikely that the upper operating pressure would be much above 9 barg.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Riko_93]

there is one issue. Consider that the design pressure max 60 psig min vaccum, and design temperature max 35 C and min 25C. I made allowance for steam cleaning condition. But can decide that the max design temperature 35C is enough for that process or i need to increase it for steam condition?

 

[LittleInch]

You might need to check with a Pressure vessel designer, but given that the steam out is short duration, you won't heat the metal up to 100C and also the pressure at when you do that operation is essentially 0 barg, I think 60 psi at 35 C should be good enough.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Riko_93]

I will. Thanks for the answer

 

[Latexman]

What is your metallurgy? For example, a lot, not all, of carbon steels have a constant allowable stress from -20^oF to 400^oF. What this means is the same thickness of metal is needed to contain a given pressure for that entire range. So, in your case there may not be a penalty for specifying min -20^oF and max 400^oF. Then, you'll be covered for steam cleaning. And in the future, if the vessel gets re-purposed, it will have a lot more flexibility. I recommend you investigate your metallurgy and talk to a pressure vessel designer.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.