1. A method for monitoring operation of a control loop in a process plant, comprising: collecting, at one or more of a plurality of computing devices, 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, wherein a load variable varies in the first operating region; determining, at one of the plurality of computing devices, an expected process gain behavior in the first operating region based on the collected process gain data, wherein an expected value of the process gain varies as the load variable varies; wherein determining the expected process gain behavior in the first operating region comprises fitting a curve to the collected process gain data, and wherein the curve corresponds to the expected process gain behavior in the first operating region; monitoring, at one of the plurality of computing devices, the process gain during operation of the control loop in the first operating region; determining, at one of the plurality of computing devices, when the monitored process gain substantially deviates from the curve corresponding to the expected process gain behavior in the first operating region; determining, at one of the plurality of computing devices, 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 curve corresponding to the expected process gain behavior in the first operating region; and generating, at one of the plurality of computing devices, an abnormal situation indicator when an abnormal situation is determined.