| Pipelines of various functions deployed in the air,underground,and structures are like blood vessels of the city and play an important role in the development of the city.With the aging ofpipeline materials,environmental changes,and the impact of human and engineering activities,pipeline leakage becomes the most critical issue in its safe operation.The effective monitoring of the pipeline is prerequisite for solving this problem.Although pipeline leakage monitoring has made great progress over the past years,traditional monitoring methods have disadvantages such as high cost,large error,and high fail-to-report rate,which are far from meeting the monitoring requirements of pipeline leakage.Fiber optic sensing technology has become a new hotspot of pipeline monitoring technology with its advantages of distributed,high precision and real-time monitoring.Based on the results obtained by our research group in the field of fiber optic monitoring,a quasi-distributed pipeline leakage monitoring sensor based on the principle of fiber Bragg grating(FBG)temperature measurement was developed for the suspended drainage pipeline.On the basis of experiments,the distributed temperature sensing(DTS)technology was applied to the fine monitoring and analysis of suspended pipeline leakage.The active heating type sensing technology was used to carry out the refined monitoring test on the seepage field of the buried pip eline leakage point source,and the accuracy was verified by numerical simulation.Finally,combined with a specific engineering monitoring project,a system for pipeline leakage monitoring was established.The effectiveness of DTS in pipeline leakage monitoring was further proved by monitoring data.The main results and findings of the thesis are summarized as follows:1.The damage caused by leakage of the drainage pipe was summarized;the advantages and disadvantages of conventional monitoring methods for pipeline leakage were summarized,and the advantages of fiber sensing technology for pipeline leakage monitoring were analyzed.2.Combining FBG temperature measurement technolo gy with liquid evaporation endothermic principle,a quasi-distributed pipeline leakage monitoring sensor was developed.The degreased cotton was determined as the evaporation material of the sensor,and the Paired-Samples T Test was used to analyze the error of the monitoring results.Quantitative analysis of the influencing factors of monitoring effect was made,such as environmental humidity,ambient wind speed,monitoring water temperature and leakage rate,found that environmental humidity,wind speed and leakage rate have a great impact on monitoring results.3.DTS technology was applied to the model experiment of pipeline leakage monitoring.For the high temperature liquid in the pipeline,the temperature variation law of the leaked liquid was analyzed.A simplified spatial resolution mathematical model was used to fit the function of the liquid heat loss after leakage and the actual temperature of the liquid.This function can be used as the alarm threshold setting basis.For the monitoring of normal temperature liquid in the pipeline,using DTS temperature measurement technology combined with the principle of evaporation endothermic was proposed.The analysis showed that a temperature difference of 2-3℃ between the leakage and non-leakage regions was produced,and the DTS spatial resolution has little effect on the temperature difference.4.Active heating sensor method was used to conduct the experiment of monitoring the normal temperature liquid leakage in buried pipeline.The influence radius of the active heating sensor was analyzed,which is generally 6cm Based on this,the point sou0rce seepage test caused by pipeline leakage was designed.The shape of the seepage field at different times were obtained,and the relationship between the wet front migration distance and time was fitted.Based on the moisture content of the drying method,the error analysis of the measured moisture content of FBG was carried out with a minimum error of only 3.43%which meets the monitoring requirements.The software Comsol was used to simulate the shape of the point source seepage field and verify the accuracy of the measured results.The effectiveness of the active heating sensor method for monitoring the leakage of buried pipelines was also demonstrated,and also provide the basis for laying sensing cables.5.Combined with the underground pipeline leakage monitoring project of Beijing Millennium Monument Hospital,a DTS fiber monitoring system for pipeline leakage was established,and the leakage alarm threshold was set according to the function of leakage heat loss and the problem temperature.The monitoring results show that the leakage position of the suspended pipeline and the temperature of the high temperature leakage liquid can be monitored by using DTS.The research results provide a new monitoring technology for pipeline leakage monitoring,and the prospect of using fiber optic technology to monitor pipeline leakage is very broad. |
