Valve Stiction Quantification Method Based on a Semiphysical Valve Stiction Model

Valve stiction is one of the most common equipment problems that can cause poor performance in control loops. Consequently, there is a strong need in the process industry for noninvasive methods that can not only detect but also quantify stiction. In this work, on the basis of a physical and a semiphysical model, a new valve stiction signature is proposed. Industrial evidence is provided to validate the new valve stiction signature. Although valve stiction is a stochastic phenomenon that can not be exactly described by any deterministic model, the revised valve signature provides a better description of sticky valve behavior, particularly when valve stiction is severe. On the basis of the revised valve stiction signature, a noninvasive, simple, and robust valve stiction quantification method is proposed using the routine operation data and limited process knowledge. The proposed quantification method estimates the stiction parameters, namely, static friction and dynamic or kinetic friction, without requiring the valve position signal. Quantification is accomplished by using linear and nonlinear least-squares methods which are robust and easy to implement. The properties of the proposed algorithm are investigated using simulated case studies of first order plus time delay processes, and the performance of the method is compared to other stiction quantification methods using 20 industrial cases.