Statistical Test-Based Practical Methods for Detection and Quantification of Stiction in Control Valves

Abstract

Control valve, affected by stiction, causes closed-loop signals to experience oscillations, which ultimately leads to a decrease in product quality, reduced plant throughput, and increased environmental footprint. Therefore, it is indispensable to detect and quantify stiction in control valves. To accomplish this objective, in the present work, four noninvasive practical and simple methods are developed with the help of statistical tests such as F-test, t-test (Student’s t-test), modified Hotelling T2-test, and reverse arrangement test (RAT). The developed methods are applied to benchmark control loops espoused from chemical, paper, and mining industries. The results of the proposed methods are compared with that of existing methods found in the literature. It is found that the t-test-based method, the modified Hotelling T2-test-based method, and the RAT-based method demonstrate equally good or better performance than the existing methods, while the F-test-based method outperforms some of the existing methods. In addition to detecting stiction, the proposed methods can quantify stiction to timely notify panel operators of stiction severity and assist plant maintenance engineers to arrange plant shutdowns well ahead in time. The proposed methods are applicable to all types of control loops except level loops.