Research On Proactive Method And Technology Of Leak Detection For Oil And Gas Pipelines

Pipeline’s small leak events are increasing fast in recent years. For the purpose ofdetecting and locating small leaks, proactive approach based on transient flow methodwas proposed in this paper. Under the transient conditions even if the leakage is verysmall, the transient waveforms will be affected by the transient flow caused by theleakage. The location of the leak will be determined accurately by using this method.The transient flow is introduced to the pipeline by controlling the valve actively, thusrealizing the active detection of pipeline leakage.The dissertation’s research work mainly covers the following aspects:First, different pipeline models was built by using fluid simulation softwareFLOWMASTER after studying the localization principle of proactive method basedon transient flow. Different valve closing time and different valve action were carriedout in the simulation research. The results showed that, when the valve closed rapidlyor acted in specific pseudo-random signals, the positioning results obtained by usingpressure transient signals would be more accurate.Time-frequency analysis was used to decompose the pressure transient signals toobtain the harmonic variation with time. Damping factors were calculated byexponential fitting. The leak position was obtained by calculating the ratios ofdifferent leak-induced damping rates. The results showed that the harmoniccomponents extracted from the time-frequency analysis results can be used tocalculate the damping rates exactly, which could improve the accuracy of leaklocation. The leakage could be as small as0.17%.A real experimental system was designed and built. A valve was installed at theend of the pipe which could be controlled to generate pressure transient signals. Highprecision pressure transducers were mounted on both the head and the end of the pipewhich are used for pressure transient signal’s acquisition. Several valves were set indifferent positions of the pipeline to simulate small leaks. Pressure transient signalswere generated by closing the valve partially in a short time for both leak and no-leakcase. Comparing the signal decay rates calculated by the traditional cycle analysiswith the time-frequency analysis, the harmonic extraction method based on thetime-frequency analysis got a better result of leak location.