Study On Leak Detection To Thermal Pipeline With Technique Of Optical Fiber Grating

Thermal Pipeline is a lifeline. The production of heat supply will be seriously affected, direct economic losses and social affection will be caused by pipeline leakage. Scientific information to pipeline maintenance is provided by discovering pipeline leakage, especially tiny leakage, the serious leakage can be prevented. So there is crucial practical significance to study on leak detection to pipeline. The leakage can be determined by monitoring the change of temperature through optical fiber sensor if the leaking hot water and surroundings have different temperature. A new method is offered to pipeline leakage detection on petroleum, nature gas, heat supply, etc in this paper.On the summary of study condition and developing trend of pipeline leaking detection, experimental research, theoretical analysis and numerical simulation on thermal pipeline leakage are made in this paper. The theoretical basis and applying experience are offered by application to practical project. The research indicates that the system can advance the modern management on pipeline course, lessen the time on fault determination, prevent economic losses and social affection and realize the continual monitor to the pipeline.The main studies in the paper are follows:1. The characteristic of sensing technique of optical fiber grating, practice application and optical fiber grating working theory is introduced; the sensitivity characteristic of optical fiber grating with stress and temperature is analyzed; demodulation method of optical fiber grating and working theory of optical fiber grating distributed system is described; the feasibility of temperature sensor system of optical fiber grating applying to thermal pipeline leakage detection is expatiated.2. The in-house experimental devices for leak detection of buried thermal pipelines is established; the temperature field of the earth on experimental model before and after leakage of buried pipelines is tested; the seepage and temperature field coupled with the leakage of pipeline is researched, and the change of earth temperature field are mapped. The experiment indicates that the leakage of thermal pipeline can be determined through the change of earth temperature field, and the results provide the basis to numerical simulation.3. Physical and mathematical models of temperature field before the leakage of the thermal pipeline are provided basing on other achievements, and infinite earth distinct is simplified to finite distinct. The temperature field of earth before leakage is used as the initial condition on calculating the unsteady temperature field of earth after leakage.On the basis, the physical and mathematical models of unsteady temperature field around pipeline in three and two dimensions after point leakage are established and corresponding boundary condition is provided. 4. The model and parameter of numerical simulation is ascertained; software Fluent is applied to numerical simulation of the temperature field of earth around pipeline in both experimental model and practical project before and after pipeline leakage; a conclusion is made on the change of unsteady temperature field of earth before and after leakage according to the numerical simulation and the relationship between quantity of leakage and the district influenced by temperature is established. Curve imitation is done. After being compared with experimental statistics, the effect is acceptable.5. According to the practical application of temperature sensor system of optical fiber grating in 10km thermal pipeline in Daqing, the design and construction experience of leak detection system are summarized, and the application effect of the detection system is proved to be possible.