Structural condition monitoring of Coriolis flowmeters through stiffness measurement

Condition monitoring of an abrasive or erosive process is essential to give early warning of potential issues and ensure safe delivery of fluid material via pipeline transportation. As one of the solutions to direct mass flow measurement, Coriolis flowmeters provide highly accurate and repeatable measurements in single phase flow processes. In some multiphase flow processes containing solid particles, Coriolis flowmeters may not perform well or even fail due to erosive wear of the measuring tubes. This paper presents an in-situ technique to monitor the structural conditions of a Coriolis flowmeter by analyzing a stiffness related diagnostic parameter in order to validate measurements or prevent flowmeter failure. This paper demonstrates the procedure to extract the stiffness related diagnostic parameter from a Coriolis flowmeter, on the basis of a mathematical model of the Coriolis oscillation system. With the aid of additional frequencies applied to the drive signal, the stiffness related diagnostic parameter of the measuring tubes is determined through frequency response analysis. This stiffness diagnostic parameter is linked to the physical stiffness of the measuring tubes by introducing a scaling factor. Furthermore, various vibration models, with different degrees of freedom and damping levels, are used to simulate the stiffness diagnostics in Coriolis flowmeters. The feasibility and repeatability of the proposed method are verified through computer simulation and experimental tests. The results show that the proposed method performs well in determining the stiffness related diagnostic parameter of a Coriolis flowmeter and hence the verification of its structural condition.