4 replies to this topic

[S J]

Dear Sirs,

 

I would like to ask about when we need to check valve failure.

Please refer to attached drawing.

When general IA failure occurs, compressor settle-out happens because all fail position of control valve indicates compressor settle-out. If check valve failure is also considered, PSV needs to be designed for check valve failure at settle-out pressure.

During HAZOP, we didn't consider simultaneous failure of IA and check valve or check valve failure at settle-out pressure.

If it's not general IA failure, PV will relieve pressure and pressure will not increase.

I'm not sure if we need to consider check valve failure when general IA failure happens or check valve failure when compressor settle-out happens.

Please share your experience if any.

 

Attached Files

•  check valve failure when settled out.pdf   51.09KB   21 downloads

[fallah]

S.J,

 

Please recheck about the location of the check valve in the schematic you uploaded...

 

Indeed, simultaneous occurrence of general IA failure and check valve failure in your case seems to be considered as double jeopardy hence shouldn't be considered as a basis for relevant design...

[Pilesar]

The check valve cannot be relied upon. Failure is not detected until demand is placed on it. Do you routinely test it and certify it to be working? If not, it is not a reliable safety device. These two failures combined do not meet the standards for 'double jeopardy' since an undetectable check valve failure is not necessarily simultaneous with the instrument air failure event.

[Pilesar]

When you assume a failed check valve concurrent with instrument air failure, you should recalculate the settle out pressure for your compressor incorporating all the available vapor volume upstream of the check valve. The resulting pressure may be substantially less than the normal settle out pressure between the check valve and the compressor discharge valve.

[S J]

fallah, Pilesar

 

Thank you for your replies.

It looks that recalculating settle-out pressure through failed check valve is correct.

 

Have a nice day.