Valve stiction is the major cause of problems in process plant control loops. It often severely reduces controller performance and the development of a method to detect stiction is required to achieve efficient operations. In this paper, a method of qualitative shape analysis is extended to deal with qualitative movements in X-Y plots. By using this qualitative analysis method, an algorithm to detect valve stiction is proposed. The detection method is applied to several control loops of a real industrial plant and shows excellent performance in detection of valve stictions.