Study On Key Technique Of Small Leakage Detection Based On Spherical Leak Detector For The Long-distance Oil Pipline

Long oil and gas pipelines play an important role in the national economy development but safety accidents also happen now and then. In the recent years, with the extension of the pipeline service time, the tiny leakage accidents caused by corrosion, aging, cracks and natural leak have become one of the major concerns for the pipeline security detection. The pipeline leakage monitoring and positioning system is developed on the base of negative pressure wave and has been applied on over 15,000 km oil and product oil pipelines successfully, which comes with considerable economic and social benefits. However, currently, the technology can only detect the abrupt gross leak. but nothing to the tiny leak. Pertaining this global puzzle that requiring urgent solutions, this essay makes an innovative contribution by proposing the detection methods for the tiny leak by equipped pipeline with spherical inner detector to cope with the tiny leak detection and positioning. This method can not only improve the sensitivity of the leakage detection substantially but also reduce most of the risk caused by the blockage of the inner detector. Focusing on the key issues related to the development of the spherical inner detector, the following four aspects were studied:(1) To ensure the detector go through vertical pipe save and sound, the fluid dynamics will be used to analyze the force condition of detector under extremely situation. It turns out that the ratio between the sphere diameter and pipe diameter and the flow velocity within the pipeline should be the two key parameters affecting the thrust on the sphere. In particular, the sphere diameter ratio would also affect the kinetic stability of the sphere in the pipeline. Hence, a simulation experiment is conducted to verify the optimal range for the sphere diameter ratio within the economic velocity of the pipeline. As per the experiment analysis, prototype is designed and developed to conduct field test of the passing ability in vertical pipe and around pipe bend.(2) The hybrid simulation of the fluid and aero-acoustics is calculated to resolve the features of the leak acoustic signal in the near-field domain within the pipeline and the extraction of the identification method. Besides, we studied the acoustic signal in the near-field domain of the leak source and the frequency distribution of the acoustic signal of the leak source and the sound field inside the pipe. The frequency and transmission characteristicsof the leakage noise in the pipeline is analyzed to acquire the relationship between different leakage rate and the acoustic signal energy by selecting the frequency band which is able to present the leakage characteristics. What is more, on the simulation leakage test platform, we verified the feasibility of detecting the leakage noise with the hydrophone, analyzed the frequency characteristics of the leakage noise and verified the simulation result.(3) In order to solve the precise positioning of the leak point, we analyzed the special contradiction of the tracking and positioning of the spherical inner detector and proposed a method to conduct precise positioning of the leak point by making use of the electromagnetic AGM and MEMS accelerometer. The features of the electromagnetic wave emited by rotating EM launcher is analyzed, and the tracking and positioning principle is verfied by the lab test. Furthermore, we analyze the precise positioning among the markers with MEMS accelerometer. Several field tests are also conducted with the two-generation prototypes we developed to prove the feasibility and precision of the locating method. The entire positioning algorithm is presented and the error analysis is made so as to acquire a method to improve the positioning precision.(4) Based on the above theoretical analysis, we developed two generations of prototype systems successively and conducted feasibility test respectively on the 2.5km water circulating pipe. Besides, the passing ability in vertical pipe and bend was also tested in the 130 m water circulating pipe. Finally, we conducted the national first field experimental use in a 77 km product oil pipeline with favorable effect.