RCA FOR 1PV-12009 suddenly open
Problem:
On Saturday the 20th of June 2009, at 11:47:06 the treated gas to flare
1PV-12009 suddenly opened which lead to Inlet feed gas pressure and
flow disturbance.
Sequence of Events:
11:47:11.3
11:47:06.7
11:47:03.7
11:46:54.1
11:45:49.4
11:45:47.2
11:44:22.6
PC12009 mode AUTO request
by the operator
PC12009 85% open
PC12009 mode MAN request by
the operator
I/O Input Failure cleared
PC12009 mode AUTO request
by the operator
PC12009 mode MAN request by
the operator
I/O Input Failure alarm received
Actions:
 Check the loop wiring found ok
 Check Analogue input cards redundancy switchover found OK
 Replaced the pressure transmitter (the most probable cause of I/O failure).
 SP-PV tracking in case of manual mode tested OK.
 “Target to Manual if Bad IN” checked and found not configured.
 Contacted Emerson ( DCS Manufacturer) to simulate and analyze the
module and assess its performance
Conclusion:
 At 11:44:22 Due to temporary fault in the pressure transmitter the PV
value at DCS is reported as Bad PV.

At 11:46:54 the pressure transmitter backed to normal and its status
became good PV, but its value took about for seconds till it reached the
normal reading 50 bars at this moment the controller react to the process
variable and it had a transient 85% open output.
Recommendations:
 To configure the PC-12009 controller to automatically switch its mode from
AUTO to MAN in case of bad PV.
 Generalize this configuration to critically similar valves according to a list
to be prepared by operation.