1. A method for monitoring operation of a control loop in a process plant, comprising: collecting process gain data associated with a first operating region of a control loop in a process plant, the control loop associated with a unit operation in the process plant; determining an expected process gain behavior in the first operating region based on the collected process gain data; monitoring the process gain during operation of the control loop in the first operating region; determining when the monitored process gain substantially deviates from the expected process gain behavior in the first operating region; and determining an abnormal situation associated with at least one of the control loop or the unit operation based at least on a substantial deviation from the expected process gain behavior in the first operating region.