Overhead Product Pressure Control Loop

Examine the overhead product pressure control loop (#33) in this distillation system (in the upper-right corner of the P&ID). Suppose PR-33 shows a pressure of 48.1 PSI, while PIC-33 shows a pressure of 50.0 PSI (equal to setpoint):

Pressure Control Loop

Identify which faults could account for the pressure indication discrepancy:

Distillation System P&ID

The below list shows some possibilities for the errors.

Identify which faults are possible and which are impossible to occur for this pressure control loop.

• PR-33 calibration error
• PT-33 calibration error
• PIC-33 (input) calibration error
• PY-33a calibration error
• PY-33b calibration error
• PV-33a calibration error
• PV-33b calibration error

Answer:

• PR-33 calibration error – Possible
• PT-33 calibration error – Impossible
• PIC-33 (input) calibration error – Possible
• PY-33a calibration error – Possible
• PY-33b calibration error – Impossible
• PV-33a calibration error – Impossible
• PV-33b calibration error – Impossible

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Credits: Tony R. Kuphaldt