4 replies to this topic

[Ghasem.Bashiri]

Dear Sir, Madam

I have encountered with ESD and PSD (Process Shut Down) in our project instrument specification.
Our specifications state that ESD loops should be SIL3 and PSD loops should be SIL2.
But we have not any clear definition for PSD.
At first I assumed that Process Shut Down means shut down that has process cause (high pressure,...) and ESD are ones that has process-non process cause (utility failure....).
But I could not find my assumption in any standards.
In our previous projects we have use PSD abbreviation for pressurized shutdown ( shut down without depressuring).
Is there any standard or specification that define PSD clearly?
Regards
A.Bashiri
Ghasem.Bashiri@gmail.com

[Padmakar Katre]

Dear,
I feel PSD is the one which we plan to have it for the maintainance of the plant purpose where we have the normal procedure and ESD is Emergency shut-down.ESD can be result of anything either your one of the utilty failure or your key equipments failure whci will cause the plant to be down.

Regards,
Padmakar katre

[gvdlans]

Why don't you ask the person who wrote the project instrument specification? That makes more sense to me than asking an internet forum... In a good specification it should have been explained.

There is no international standard on what psd can mean so we can only guess...

[Zauberberg]

Bashiri,

PSD is related to Process Shut Down conditions - in simple words, it means that shutdown system will activate as soon as any of the process variables within PSD logic reaches certain (pre-defined value).

Examples: fired heater shutdown in case of low feed flow, or low fuel gas pressure. Or, pump shutdown in case of low suction pressure etc.

[Zauberberg]

Bashiri,

To give a more useful answer to this query, I made one search regarding terms PSD/ESD and here are the results:

- Process ShutDown (PSD) system is a part of plant (facility) safegarding system with a purpose to minimise the frequency and consequences of excursions outside the facility operating envelope.
- Emergency ShutDown (ESD) system is a part of plant (facility) safeguarding system with a purpose to keep the process within the design envelope and to prevent the escalation of abnormal conditions into a major hazardous event.

The PSD and ESD can be considered as Effects, which are triggered by certain Causes. The PSD and ESD are levels of shutdown which discriminate between the seriousness of the Causes leading to the appropriate Effects.


Regards,