ASC LIMIT PRESSURE active and ASV open although Deviation was high.

For our reminder in the future.

Operator team inform that there were process anomaly at 22:00 pm 20 January 2018 :

1.       Speed Turbo expander increase from 6,300 rpm to about 7,100 rpm, then operator compensate by increase IGV opening from 58% to 72%

2.      ASV Booster GEC Tr 3 opening to 70%, previously only 7% opening at the evening.

3.      ASC Booster compressor GEC Tr 3 deviation (DEV) = 0.5, which is operating point at save point (far away from surging line).

4.      Suction pressure booster comp GEC Tr 3 at PT_6212 was 135 psig (input for ASC) and PT_6214 was 140 psig (for indication only).

Then we compare the reading by install local Pressure Gage and indicated 140 psig. (existing local Press Gage was broken then replace the local PG).

Both of these Press Transmitter at the same line.

5.      LIMIT led illuminate and then press the LIMIT3 button and show setpoint 135 psig as the control mode.

Setpoint suction pressure @ MPIC = 140 psig

Setpoint suction pressure @ ASC = 135 psig

Based on 5 fact above then we discussed with team we decided to  replace PT_6212 by put the GEC tr3 at idle condition.

The consideration were :

1.      LIMIT led active and then we press LIMIT3 and shown 135 psig (suction pressure) as the control mode which trigger LIMIT led to active.

2.      LIMIT led illuminate when PT_6212 hit 135 psig, by hit this 135 psig setpoint, then the ASV opening will increase to maintain suction pressure keep at 135 psig.

3.      Compared pressure reading PT_6212 was 135 psig  but PT_6214 and local pressure gage were 140 psig.

4.      ASV open excessive only occurred at GECT tr3, while GEC tr 1 all ASV were close, this means that the problem located at ASV or ASC booster comp GEC Tr3

We decide to execute at idle condition instead of activated MOR ON due to safe operating condition.

Alhamdulillah after replacement of PT_6212 then we load GEC TR 3 in normal condition.