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Automation projects concerning the operation of long pipelines aim to not just improve the operational activities but also contribute to the safety of the facilities and reduce any potential environmental impact of the activity. It is common knowledge that oil companies need to have their pipelines flowing fully pressurized so that its contents can be controlled and accounted for. Therefore, many companies have installed automated control valves at arrival point of the pipelines in order to guarantee that the pressure inside the pipeline is optimal and controlled. This operation has led to important studies in control theory and Proportional, Derivative and Integrative control systems PID. Several articles study methods and optimal gains for the precise positioning of the control valve. The problem presents itself when the valve is required to compensate a severe change in the pressure set point. For instance, if one pump is disconnected from the pipeline by a safety-automated measure in a multi-pump scenario, the rapid movement of the control valve may result in an undesired large overshoot and stabilization period. This can be observed in small diameter or short pipelines in which the system responds fast to any alteration in the control valve position. This behavior can not always be compensated by altering the gains of the PID controller as they are set to work on the most common scenario and can only be expected to correctly respond when the changes in pressure are sufficiently small. Faced with this problem in a pipeline, the engineers and technicians of an oil company installed a pressure set point curve in order to avoid the described behavior of the valve, even if momentarily depressurizing the pipeline. Throughout this article, the results of this alteration are described and it is suggested ways to further improve the control system without jeopardizing the safety of the pipeline operation. |
