Leak detection in pipes by frequency response method.

摘要

This dissertation presents a new procedure based on the frequency response method to detect leakage in piping systems. Two different approaches were developed. In the first approach, a steady-oscillatory flow, produced by a periodic opening and closing of a valve at the downstream end of the pipeline, is analyzed in the frequency domain by using the transfer matrix method. In the second approach, transient flow produced by a non-periodic gradual opening or closing a valve is analyzed in the time domain by the method of characteristics and the results are transformed into the frequency domain by the fast Fourier transform.; A frequency response diagram is prepared in both approaches. The frequency response diagram of a system with leaks has additional resonant pressure amplitude peaks (herein called the secondary pressure amplitude peaks) that are lower than the resonant pressure amplitude peaks for the system if there were no leaks (herein called primary amplitude peaks). The location of a leak is determined from frequencies of the primary and secondary pressure amplitude peaks and the leak discharge is determined from the maximum and minimum discharge amplitudes.; The reliability of the other presently available real-time leak detection methods depends on extensive measured data at different locations on the pipeline, which in most cases are not easily available, and on the system parameters, such as pipe friction. The method presented herein requires measurements at the valve location only. It is applicable for practical values of the friction factor over the range 0.01 to 0.025. This method can be used to detect leaks in real-life pipe systems conveying different types of fluids, such as water and petroleum. It can be used directly by comparing the frequency response diagram of a modeled system without leaks to the frequency response diagram developed by either experimentally oscillating a valve or gradually opening or closing a valve at the downstream end of a pipe and taking measurements of pressure head and discharge at the valve location.