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How to naming the interlock number in P&ID

How to naming the interlock number in P&ID

Dear pro eng-tips members

There is two pumps(A/B) which one is running, and the other is spare.

Spare pump is arranged for automatic staring whenever loss of the pumping service for more than a short period of time would cause a unit shutdown.

And, it should be select the most appropriate variable that it will take a short amount of time to bring the spare pump up to speed and re-establish flow. Therefore, the point at which the spare is started should be as close to the
normal operating point as possible without causing excessive spurious starts.

It is particularly important to review the auto start setpoint versus the set point used to shut down equipment in the event the process variable is lost. There must be sufficient margin in the auto start and shutdown setpoints to allow time for the spare pump to start and re-establish the variable and to
allow for instrument drift over time.
Sorry, there is a little bit disgress.

Here the case is used a variable, flow to automatically start a spare pump. The FT-A1/FC-1 low low flow on one pump A or B autostarts other pump if available.

Unfortunately, the interlock for the pump didn't show any tag on the P&Id. I wonder that it is proper to name a tag number for this interlock or just left it blank cause there is no any information for the numbering in the cause effect table and control logic document.

Could any pro member to share what is rule in naming the interlock number ?

Thank you very much.   

RE: How to naming the interlock number in P&ID

There is no univeral or widely accepted device or equipment or logic tagging system or convention.  ISA has some suggested standards.  All larger companies have developed some sort of standard so that their controls and process engineers can communicate and work together and with operations and maintenance.  If your control is local (not at a PLC or DSC or central control panel), some places don't name one, they just show the dashed or other line to a local logic control or switch, and show no number or name.  If it goes to or thru a central control, everyone shows some designation so they can communicate without or with minimal confusion.  That is the purpose of engineering documentation.


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