19 replies to this topic

[Tran]

Dear all,

 

I see in some project they calculate the design pressure as 105% of Maximum operating pressure (PZHH set point) for all range of working pressure, but it's not stated what standard was referred. The only one standard that I know related to this is Norsok P001, however it seem not applied here as the rule in Norsok P001 is different.

 

Can anyone advise 105% is based on which standard? or it's just a normal practice?

 

Thanks a lot for your help!

[Julien123456789]

Tran,

It depends on what range of your working.

API 520/521 or API 2000 may be referred.

 

Julien.

[fallah]

Tran,

It depends on what range of your working.

API 520/521 or API 2000 may be referred.

 

Julien.

 

Julien,

 

API 520/521 or API 2000 might be included a general definition of design pressure but what really included a practical definition of it is design criteria of each project or normal practice of each company. Some propose 10% above max operating pressure, some 5% or even a little higher or lesser...

[Tran]

Dear Julien and Fallah,

 

Thanks for your comment. Actually I have read API 520/521 many time and there is no specific value there. As Fallah said it just general definition. So it's clear that 105% is not based on standard but just the  normal practice.

[Julien123456789]

Tran,

This is a very typical question.

In fact, it depends on your application.

As a process engineer, you will define it and then you need to refer your supplier for a confirmation.

 

Julien.

Edited by Julien123456789, 11 April 2016 - 05:15 AM.

[Bobby Strain]

A number of engineering companies use rather elaborate scenarios to arrive at design conditions for piping systems. So, you don't have complete answers to your query yet.

 

Bobby

[Julien123456789]

A number of engineering companies use rather elaborate scenarios to arrive at design conditions for piping systems. So, you don't have complete answers to your query yet.

 

Bobby

 

I completely agree with you.

That's why I suggested TRAn to analyze his application. However, do not confuse design conditions with accident conditions.

It should be investigated for an adequate answer.

 

Julien

Edited by Julien123456789, 11 April 2016 - 12:19 PM.

[Tran]

Gents,

 

Thank you for your advice! My problem is I have a centrifugal compressor with shut in presusre 220 barg. The piping downstream of compressor have design pressure 160 barg being protected by PSV (pilot type) set @160 barg and PZHH set@ 156 barg which will trip the compressor.

 

Due to the production demand, we are considering to increase PZHH to 157 barg, over pressure is not a concern as the compressor will trip imediatly when the PZHH trigger. But then we will face the chattering issue of the PSV. As I refer Nosork P001, it is allowed to set the PSV higher than design pressure for piping, but a examination of the relevant piping design code is required. bellow is quoted from Nosork P00:

 

For piping being protected from overpressure by a PSV, it is allowable to have a PSV setpoint above the design pressure of the piping for some piping design codes. This shall be evaluated for each case, and only applied after examination of the relevant piping design code. 

 

So can anyone advice what we need to examine from the piping design code? In my case the design code is ASME B31.3.

 

Thank you very much!

[fallah]

 

Thank you for your advice! My problem is I have a centrifugal compressor with shut in presusre 220 barg. The piping downstream of compressor have design pressure 160 barg being protected by PSV (pilot type) set @160 barg and PZHH set@ 156 barg which will trip the compressor.

 

Due to the production demand, we are considering to increase PZHH to 157 barg, over pressure is not a concern as the compressor will trip imediatly when the PZHH trigger. But then we will face the chattering issue of the PSV. As I refer Nosork P001, it is allowed to set the PSV higher than design pressure for piping, but a examination of the relevant piping design code is required. bellow is quoted from Nosork P00:

 

For piping being protected from overpressure by a PSV, it is allowable to have a PSV setpoint above the design pressure of the piping for some piping design codes. This shall be evaluated for each case, and only applied after examination of the relevant piping design code. 

 

So can anyone advice what we need to examine from the piping design code? In my case the design code is ASME B31.3.

 

 

Tran,

 

You can find your query in Sec. 302.2.4 (f) of ASME B31.3-2010, "Allowances for Pressure and Temperature Variations"...

 

In above mentioned section limitations for higher pressure than the design pressure in process piping under ASME B31.3 being stated...
 

[Tran]

Thank you so much, Fallah!

[Julien123456789]

....But then we will face the chattering issue of the PSV...

 

 

 

Tran,

Could you please explain why do you face a chatting issue when changing PZHH set from 156 barg to 157 barg ?

Edited by Julien123456789, 12 April 2016 - 03:05 AM.

[fallah]

 

....But then we will face the chattering issue of the PSV...

 

 

 

Tran,

Could you please explain why do you face a chatting issue when changing PZHH set from 156 barg to 157 barg ?

 

 

Because the set pressure of PZHH becomes very close to PSV set pressure...
 

[Julien123456789]

 

....But then we will face the chattering issue of the PSV.

 

Tran,

Could you please explain why do you face a chatting issue when changing PZHH set from 156 barg to 157 barg ?

 

 

Because the set pressure of PZHH becomes very close to PSV set pressure...
 

 

 

Mr. Fallah,

I think that chatting issue comes from PSV blowdown pressure but not PSV set point.

Explain me if I am wrong.

 

Julien

[fallah]

 

 

 

 

Because the set pressure of PZHH becomes very close to PSV set pressure...
 

 

 

Mr. Fallah,

I think that chatting issue comes from PSV blowdown pressure but not PSV set point.

Explain me if I am wrong.

 

Julien

 

 

Julien,

 

Pilot operated PSV's have lower blowdown pressure. Then if the PZHH as the limit of operating pressure to be very close to PSV set pressure; it might by PZHH increment the new set point to be higher than PSV blowdown pressure and the chattering due to this fact would be possible...
 

[Julien123456789]

Mr. Fallah,

Thank you so much or your clear explanation.

 

Assuming piping design pressure at 160 barg.

In case of this study, what will be consequences if we increase PSV set point from 160 barg to 161 barg while changing PZHH set from 156 barg to 157 barg.

 

I would like to ask this question after inquiring Sec. 302.2.4 (f) of ASME B31.3-2010  and Nosork Code as you and TRAm mentioned.

 

Is feasible this solution in reality ?

 

Julien

Edited by Julien123456789, 12 April 2016 - 04:59 AM.

[fallah]

 

Assuming piping design pressure at 160 barg.

In case of this study, what will be consequences if we increase PSV set point from 160 barg to 161 barg while changing PZHH set from 156 barg to 157 barg.

 

I would like to ask this question after inquiring Sec. 302.2.4 (f) of ASME B31.3-2010  and Nosork Code as you and TRAm mentioned.

 

Is feasible this solution in reality ?

 

 

Julien,

 

You are not allowed to set the PSV at a pressure higher than downstream piping's design pressure; because their might be a case following which relieving from the PSV can be continued higher than the limitations stated in mentioned section of ASME B31.3....

 

 

[Julien123456789]

Mr. Fallah,

I am aware of what you mean.

However, as quoted post #8 of TRAm or even section 302.2.4 of B31.3

 

For piping being protected from overpressure by a PSV, it is allowable to have a PSV setpoint above the design pressure of the piping for some piping design codes. This shall be evaluated for each case, and only applied after examination of the relevant piping design code. 

 

That's why I asked you this question.

Am I misunderstanding the codes ?

 

Julien

[Padmakar Katre]

Dear all,

 

I see in some project they calculate the design pressure as 105% of Maximum operating pressure (PZHH set point) for all range of working pressure, but it's not stated what standard was referred. The only one standard that I know related to this is Norsok P001, however it seem not applied here as the rule in Norsok P001 is different.

 

Can anyone advise 105% is based on which standard? or it's just a normal practice?

 

Thanks a lot for your help!

Hi,

At higher operating pressure, few companies follow 5% margin over operating to set the design pressure than 10% due to purely economics.

[shantanuk100]

Hi Tran,

 

Check the links below for some guidelines on Vessel Design pressures, operating pressures, set and Relief pressures.

http://www.cheresour...-psv-setpoints/

http://www.cheresour...nketing-system/

 

Download the documents attached in the links and try to understand them completely.

I would also suggest going through the relevant sections in API 520, 521, and 2000.

 

Regards,

Shantanu

Edited by shantanuk100, 13 April 2016 - 12:10 AM.

[Tran]

Dear all,

 

Thank you very much for your valuable help! 

 

Regards,

Tran