7 replies to this topic

[dhns]

Dear all,

could you please explain anybody about ..to fix the design temperatue and pressure
for any process vessels
for examble one seperator is operating in 70 deg and 12 barg
what may the design temperature and pressure ?
is there what are the major factors will have to be considered ?
please explain.,
thanks in advance
regrds,
dhns.

[Root]

Hi dhns,
For which service you want use this separator, mostly temp and pressure values depend on service of the equipment.
If you are new for designing of equipment, then you go through the Turton's "Analysis, synthesis and design of chemical Process"
This book will give you guide line for designing of equipment and process.There is more book "Chemical equipment selection and design"
Hope this will help you

Toor

[aluma]

The design temperature and pressure is often some percentage above the normal operating conditions. Additional factors to be taken into account are the severity of the process and integration of the equipment with utilities.

[ARAZA]

Dear all,

could you please explain anybody about ..to fix the design temperatue and pressure
for any process vessels
for examble one seperator is operating in 70 deg and 12 barg
what may the design temperature and pressure ?
is there what are the major factors will have to be considered ?
please explain.,
thanks in advance
regrds,
dhns.

Dear dhns,

To fix the design conditions for any process equipment is a complicated job, one must understand the process completely before specifying any design conditions. Than use your experience and judgement. The important factors to be considered are any updset conditions that might prevail due to any human error or other utilities failure such as loss of instrument air, power etc.

To specify the design pressure, consider pump shut-off pressure if there any pump in the system. The pump shut-off presure would be the design pressure of the process lines and the equipment. However, any design pressure would be limited by any PSV installed in the system. If there are no credible process upset, use op. pressure X 1.5 for the deisgn pressure, if your op. pressure is less than 1000 psig, if more use a factor of 1.6.

To specify the design temp, consider any process updet such as loss of cooling water, loss of power, steaming etc. IF there are no credible scenario. Consider 50 deg F + op. temp = design temp.

Hope this helps

Araza

[Andrei]

Dear Araza,

If everybody would fix the design pressure and temperature of vessels using your figures the plants would be so expensive that nobody would afford to build anything. It may be valid in some very high risk plants like nuclear and explosive materials handling.
There is a 1.5 factor involved somewhere, but that is used for hydrotest pressure, not the design pressure.


dhns,

ASME Code Section VIII is the one that describes how to deal with these things. I reccomend to have a look at the API Recommended Practice 521, for a better understanding of how each pressure level is fixed. There is a very clear diagram showing all the pressure levels at page 30 of 1997 edition.
In general design pressure and design temperature are a function of maximum normal operating pressure/temperature plus a design margin (safety factor). This can be 10 to 20%.
Maximum normal operating pressure/temperature doesn't include human error, or process upsets or fire, for those kind of events there are protective devices (PSV's are some of them) that have to be considered during design pressure/ temperature selection.
All the respected engineering companies are providing a Design Pressure/Temperature Diagram of the plant that show all these values consistent on one document.

Be safe,
Andrei

[Padmakar Katre]

Dear all,

could you please explain anybody about ..to fix the design temperatue and pressure
for any process vessels
for examble one seperator is operating in 70 deg and 12 barg
what may the design temperature and pressure ?
is there what are the major factors will have to be considered ?
please explain.,
thanks in advance
regrds,
dhns.

Dear,
This could not be a general question. Beacuse you will get or infact anyone else will get the general reply to this kind of query. Are you talking about the new project or an existing unit. As I have seen the cases in Revamp where exsiting equipments are retained by providing the PSV's so please be specific. There are number of factors which are considered while giving the design conditions like pressure and temepratures.
In a new project its always mentioned in the Design basis for the Design temperatures i.e. how much marging to be kept while fixing the design temperature w.r.t. the normal operating temperature. The Design Pressure decision is taken on the basis of the Equipment location in your Circuit. If it comes in the discharge of Pump then it will designed for the Shut-Off head of the Pump and so.
If the equipment is not in the pump circuit which will not experience the Pump Shut-off in the blocked outlet condition then you could follow the guidelines given by the other Che Members.

[engprocess]

Dear all,

could you please explain anybody about ..to fix the design temperatue and pressure
for any process vessels
for examble one seperator is operating in 70 deg and 12 barg
what may the design temperature and pressure ?
is there what are the major factors will have to be considered ?
please explain.,
thanks in advance
regrds,
dhns.

Dear,
This could not be a general question. Beacuse you will get or infact anyone else will get the general reply to this kind of query. Are you talking about the new project or an existing unit. As I have seen the cases in Revamp where exsiting equipments are retained by providing the PSV's so please be specific. There are number of factors which are considered while giving the design conditions like pressure and temepratures.
In a new project its always mentioned in the Design basis for the Design temperatures i.e. how much marging to be kept while fixing the design temperature w.r.t. the normal operating temperature. The Design Pressure decision is taken on the basis of the Equipment location in your Circuit. If it comes in the discharge of Pump then it will designed for the Shut-Off head of the Pump and so.
If the equipment is not in the pump circuit which will not experience the Pump Shut-off in the blocked outlet condition then you could follow the guidelines given by the other Che Members.

if it is a new project, you have to have in the BOD all parameters that you need, if not I will just give you a range how to design a pressure of an equipment:
1- maximum operating pressures between 10 and 50 barg add 15% to the maximum operating pressure.
2 - maximum operating pressuregreater than 50 barg add 10% to the maximum operating pressure.
3- for maximum operating pressures below 10barg add 2 bar to the max operating pressure


hope these information will help you
EngProcess

[vinay]

Dear all,

could you please explain anybody about ..to fix the design temperatue and pressure
for any process vessels
for examble one seperator is operating in 70 deg and 12 barg
what may the design temperature and pressure ?
is there what are the major factors will have to be considered ?
please explain.,
thanks in advance
regrds,
dhns.

Further to what others have added , I would like to tell you that the information you are seeking may vary from different process licensors or detail engineering contractors / industry to industry. For example if you are designing something for nuclear power plant the design pressure could be as high as 1.5 times operating pressure as stated by ARAZA.

However if you are designing the equipment for refinery/chemical plants the following guidelines are generally used by major licensors.

• Set design pressure a minimum of 25 psi (1.75 kg/cm2) above maximum normal operating pressure with 50 psig (3.5 kg/cm2 (g)) as a minimum design pressure for low pressure equipment.

• Set design temperature a minimum of 50°F (28°C) above maximum normal operating temperature with 250°F (120°C) as a minimum design temperature for low temperature equipment.

• Set design pressure at 110% of maximum normal operating pressure when operating pressure is above 250 psig (17.5 kg/cm2(g)).

• Set design pressure for equipment that can be blocked in down stream of pump, equal to estimated pump shutoff pressure; i.e. maximum suction pressure generally under relieving conditions plus 1.25 times the pump rated differential pressure.

However as i stated this depends from company to company & industry to industry. You should consult some senior engineers in your unit before taking any decision.

Regards,
Vinay Mathur