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Psv Blowdown - Operating Pressure

psv safety valve blowdown

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#1 HLO

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Posted 11 April 2018 - 02:16 PM

Dear all,

 

For a PSV in steam service, we have an operating pressure of 46 barg and a set pressure of 50.6 barg (coincident with MAWP). One supplier indicated that the op. pressure shall be reduced to 45.5 barg, to allow a required gap of 10% between operating and set pressure.

 

We cannot modify the operating pressure nor the set pressure (since is equal to the MAWP). My question is: assuming an op. pressure of 46 barg, at some stages of the closing travel we will have pressure lesser than 45.5 barg at PSV's disc, due to the dP in the inlet piping (near 2.4% at rated flow). This disc pressure will increase while flow decrease, up to 46 barg. But, the PSV will be already closed. So, for the reclosing (without seen others effects that could excert to have closer oper./design pressure), could I be confident that there will be not issues?

 

Of course this will be reviewed with supplier, but I would to know your valuable opinions.
 

Thanks!

 

 

 

 



#2 fallah

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Posted 11 April 2018 - 02:31 PM

 

For a PSV in steam service, we have an operating pressure of 46 barg and a set pressure of 50.6 barg (coincident with MAWP). One supplier indicated that the op. pressure shall be reduced to 45.5 barg, to allow a required gap of 10% between operating and set pressure.

 

We cannot modify the operating pressure nor the set pressure (since is equal to the MAWP). My question is: assuming an op. pressure of 46 barg, at some stages of the closing travel we will have pressure lesser than 45.5 barg at PSV's disc, due to the dP in the inlet piping (near 2.4% at rated flow). This disc pressure will increase while flow decrease, up to 46 barg. But, the PSV will be already closed. So, for the reclosing (without seen others effects that could excert to have closer oper./design pressure), could I be confident that there will be not issues?

 

Of course this will be reviewed with supplier, but I would to know your valuable opinions.
 

 

HLO,

 

The operating pressure of your system is around 91% of the PSV set pressure and IMO with blowdown of 5% and tolerance of +/- 3% on set pressure there would be no important issue regarding the PSV reclosing...



#3 HLO

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Posted 11 April 2018 - 02:38 PM

Thanks for your reply, Fallah!. The 5% that you mentioned is a general value or is required by a code? I'm looking at the codes but it's not clear for me.



#4 fallah

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Posted 11 April 2018 - 03:00 PM

Thanks for your reply, Fallah!. The 5% that you mentioned is a general value or is required by a code? I'm looking at the codes but it's not clear for me.

 

HLO,

 

It's a general value which you can specify in PSV data sheet and ask vendor to apply in PSV design...



#5 HLO

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Posted 11 April 2018 - 03:42 PM

Thanks again. We will discuss that with the supplier.

 

Nevertheless, just to learn, is my reasoning above OK? I'm starting to think that not...






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