Extended Blockage Detection in Pipes Using the System Frequency Response: Analytical Analysis and Experimental Verification

Extended blockages in a pipeline system are expected to impose changes onto the system resonant frequencies where the size and nature of the frequency shifts can be used to determine the blockage characteristics. Although a theoretical method for detecting and locating extended blockages in pipeline systems using these changes in the system frequency response (SFR) was developed by the authors in a previous paper, the impact of an extended blockage on SFR has yet been verified experimentally and is the topic of this paper. The impact of six different extended blockages under a range of different Reynolds numbers on the frequency response is used to confirm the theoretical behavior of an extended blockage. These experimental tests are conducted in the pipeline hydraulic laboratory at the University of Canterbury, New Zealand. An analytical simplification of the original SFR-based method is used to identify the key blockage parameters governing the frequency shifts and shows that the magnitude of the frequency shift increases with severity of blockages and is related to the changes in characteristic impedance and wave propagation coefficient of pipeline (pipe diameter, thickness, and/or wavespeed) imposed by the blockage. The experiments show that the length and location of potential extended blockages in the pipeline can be accurately predicted by the proposed method. Significant error exists, however, in the prediction of the pipe constriction diameter and is a result of the nonlinear operations in the experiments such as full valve closure in this study and the inability of existing models for perfectly replicating transient events in pipes with severe constrictions. (C) 2013 American Society of Civil Engineers.