Design Of Distributed Fiber-optic Underwater Long Oil-gas Pipeline Leakage Detection Device

Submarine pipeline’s role in the development of offshore oil and gasindustry has become increasingly evident, there will be a significant safety accidentonce leaking. Combined with the PGC demodulation, DSP signal processingtechnology, and the improved distributed fiber-optic interferometer which is basedon the mixed principle of Sagnac and Mach-Zehnder, an underwater long Oil-Gaspipeline leakage detection device was designed in this project which is supported bythe National Natural Science Foundation of China and the National Industry PublicWelfare Project.First of all, the principle of the mixed distributed fiber-optic interferometer wasanalyzed in the dissertation, the important parameters in the structure were studied,positioning methods were deduced by the mathematical formulas. At the same time,the theoretical derivation for the polarization state of the system structure was doneby using the Jones matrix, then an improved distributed fiber-optic interferometerwas proposed.According to the leakage signals of pipeline are nonlinear, tiny broadbandsignals, and there is a lot of background noise in the testing environment, the pipelineleakage signal de-noising and zero frequency search was studied in this dissertation.The leak signals were preprocessed, which is based on the discrete wavelet and theleast squares curve fitting method. Reusing the signal through multi-scaledecomposition of each signal multiplication method to determine the leakage nullspectrum, and a certain result was got.Then, the optical fiber interference signal demodulation and signal processingtechnology is researched, the the PGC phase demodulated interference signaldemodulation circuit module for optical fiber and the signal processing circuit systemwhich is based on DSP28335is constructed. The pipeline leak detection systemwhich is based on the mixed distributed fiber-optic interferometer was completed. What’s more, the corresponding slave computer control software and host computersoftware system were developed.In the last of the dissertation, the different leakage points are measured. And thedifferent delivery pressure, the optical fiber cladding material, the polarization statesof light, pipe material and so on were tested on the influence to the detectionperformance of the system. At the same time, the single point and multi-point leakpositioning technologies were researched, the improved methods of the detectionperformance.were proposed.Through the experimental studying, it could be found that the system detectionhas a good performance and a friendly human-computer interaction interface. It cantest the leak point of the underwater long oil-gas pipeline, whose leakage aperture ismore than2.5mm and the total length is10km, and the leak of absolute positioningerror is not more than170m. A foundation for the realization of the underwaterlong-distance pipeline safety monitoring is provided.In view of the work for the dissertation, some existing shortages were pointedout in the final summary. According to the existing problems, a forecast was madefor the content and direction of the follow-up work.