2 replies to this topic

[SawsanAli311]

Hi, 

 

I would like to get your feedback regarding whether the code allows to have a link between an ESD trip singal acting on its final SIF elements (SDV) in addition to sending a signal to another DCS pressure control loop to change the controller output to higher opening of a PCV for example. The reason for such a proposal is to help in mitigating pressure build up at the suction of a tripped compressor. 

 

Since control DCS elements are not SIF and hence cannot be SIL assessed, I am doubting whether it is acceptable to take credit for the above described linking action between ESD and DCS.

 

Appreciate your feedback and views based on your experience. 

 

Regards, 

[Faisal Ghafoor]

In SIL / HAZOP study, you will still give credit of 0.1 (PFD) risk reduction in case some control valve is being operated with ESD interlock. With this 0.1, you can assess either you still need extra layer of protection.

[Whit123]

If you are using the same signal for both, then the DCS is not an independent layer of protection, so you cannot take credit for it. You can allow the ESD trip signal to also actuate an alarm or other interlock in the DCS, but in a way that the ESD will send the signal to the DCS and this arrangement should not negatively affect the ESD trip. (For example a fault in the signal connceted to the DCS should not prevent the ESD from actuating).