Credibility of Piping Pressure Transient Measurements Using Strain Gauges

摘要

The use of strain gauge measurements to determine the pressure transient history signature inside the pipe, Szasz [1], needs to be reexamined. Computation of the natural frequencies of the pipe shell vibrations, Leissa [2], including FSI, Ibrahim [3], should precede these measurements. The pressure disturbance signature and its traveling velocity interact dynamically with the pipe shell natural vibration mode shapes and frequencies. The latter have detrimental effects on the measured response magnitude as well as the response signature configuration, Meirovitch [4]. In addition, traveling pressure propagating velocity near or at resonance with the cylindrical shell mode shape distorts and over amplifies the strain gauge transient response. There is no direct technique to back transform the strain response history signature into its original driving pressure history, Leishear [5].In this paper the dynamic response for a simply supported circular cylindrical shell pipe model is formulated. The pressure transient history signatures are simulated as mobile concentrated radial ring force, traveling step pressure shock front, and propagating acoustic harmonic pressure wave. Comparisons between the projected hoop strains obtained based on the equilibrium of the pressure forces [1], and the hoop strains determined from the shell dynamic response are examined.At least two sets of strain gauge bands are needed to confirm the validity of the measured strain data. Limitations on the appropriateness of deploying strain gauge bands as a mean to measure the traveling pressure history inside the pipe are delineated in this paper. Generally, steam transporting pipes are less influenced by these limitations than liquid transporting pipes.