Quantification of valve stiction based on a semi-physical 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 non-invasive methods that can not only detect but also quantify stiction. In this work, a semi-physical valve stiction model is derived from the analysis of the dynamic response of a physical model. Based on the semi-physical model, we propose a noninvasive valve stiction quantification method using the routine operating data from the process. The algorithm is proposed to estimate 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. Several simulation examples, including both self-regulating and integrating processes with different degrees of stiction, are used to demonstrate the effectiveness of the method.