Recently there was a case of loss of gas oil cracking unit feed resulting in unit shutdown. During troubleshooting analysis, it was observed that the centrifugal pump feeding the gas oil feed suddenly experienced a drop in the motor amperage a few seconds before the total gas oil flow to the pump started to drop below the minimum circulation flow. The minimum circulation control valve fortunately worked when it started to open to allow the circulation flow back to the pump suction.
Everything was checked, from NPSHa of the pump, basket strainer and y-type pump suction strainer, total gas oil and high-pressure reactor feed controllers` transmitters, as well as the pump motor voltage, among others. But none seemed to be identified as the root cause of the unit trip.
Is there any other aspects of the centrifugal pump that needs to be evaluated? Any possibilities of internal circulation inside the pump cavity that could cause the sudden pump cavitation?
Test runs on the pump's spillback have been conducted, and based on the observation, all including the pump vibration and behaviour of the minimum circulation control valve opening, were considered normal.
Could the pump motor amperage drop result in lower suction feed to the pump?