Review and comparison of techniques of analysis of valve stiction: From modeling to smart diagnosis

Abstract The importance of evaluating valve conditions and detecting the onset of possible malfunctions is recognized as a key issue in control performance monitoring, as they may affect heavily the loop operation and have a direct influence on product quality and then plant economy. In particular valve stiction, a phenomenon which shows itself with similar effects to other causes (as incorrect tuning, external disturbance), but requires specific interventions to eliminate it. This paper aims to be a review of the state of the art about valve stiction, by covering fundamental and applicative issues, classical and innovative approaches. Being a comprehensive review paper, the approach of presentation of the examined material necessarily follows the categorization of previous survey papers (which are carefully acknowledged). Techniques illustrated in each category are compared pointing out analogies and differences, showing more appealing features and possible points of weakness. In most cases, comparative application on industrial data is performed, and some guidelines for the choice of best methodologies are provided. These aspects have to be considered as added values of the work. The paper starts with an illustration of basic aspects of the phenomenon of valve stiction, with description of its origin and physical mechanisms, and details about the effects on control variables. Then, different models of valve stiction are examined, and traditional detection techniques and smart diagnosis approaches, based on additional measurements, are presented. Then, the paper illustrates identification and quantification methods, compensation techniques, and software packages proposed for control loop performance assessment.