Study On The Speed Control Of Magnetic Flux Leakage Detector In Gas Pipeline

Long-distance gas pipeline is the main way to transmit Chinese natural gas. The safe operation of the pipeline is considered as the major political and economical issue for China. Regular pipeline inspection is an important path to ensure the normal operation of the pipeline. Gas pipelines are mostly buried underground or underwater, thus detection technology in the pipeline is globally recognized as the most effective detection method of gas pipeline. Among so many detection technologies the magnetic flux leakage inspection which can operate in the formidable environment with high detection accuracy is most widely used. If the detector runs too fast the testing results can not even detect pipeline drawbacks, thus pipeline detector based on the magnetic flux leakage inspection technology requires a decent speed. Controlling the detector’s speed which makes it runs within a reasonable speed range plays an important role to improve accuracy. Aiming to the troubles of the detector’s controlling speed which is closed to actual needs, by using theoretical analysis and experimental system analysis and by analyzing pipeline flow field of the detector during the operating state. In-depth studies of discharge mode and pressure regulating way to adjust the detector speed have been discussed in this paper.The interaction among the pipeline flow fields and running detector through the pipeline has been studied. Application principles of fluid mechanics, detection is in the discharge area where the flow field model has been constructed; by using dynamic grid and self-defined functions, the entire starting process of the detector in the horizontal straight pipeline is simulated; Analyzing the flow field parameters such as gas velocity, pressure etc to affect the speed of the detector with different discharge area; Under the certain operating conditions by using the simulation tools the detector’s actual speed can be speculated.The method to adjust the detector speed has been deeply studied here. After analysis the speed of the detector will be determined when the detector is accelerated after getting blocked and in the normal state. After the analysis and experiments, the detector acquires speed signal from odometer wheel; adjust the detector speed by setting up different openings of the discharge area; Control model is constructed by experimented values during the normal operation. After getting blocked in the acceleration process, the detector speed signal can’t be collected effectively as the odometer wheel skids and as a result detector’s speed will lose its control. By analyzing the above mentioned problem, an accelerometer is installed in the detector to solve the problem that the odometer wheel can not collect speed signal when the odometer wheel are skidding. Analyzing the structural characteristics of the gas pipeline and ignoring the small factor associated with the detector speed, the gas pipeline model has been simplified to the horizontal straight pipe, uprising sloped line, the vertical rising line, downward sloping line, vertically dropped line and several types of two-dimensional pipelines. According to the mechanical analysis the relationship between the detector’s speed and discharge area is obtained by deducing the acceleration control model. By using the accelerometer and inclinometer, the acceleration value and the traveling direction can be acquired respectively to determine the parameters of the acceleration control model. The fusion of speed control model and acceleration control model will establish a new model so that it can control the detector’s speed under different operating conditions. Simulation is accomplished. From the results of simulation under certain operating conditions, the detector’s speed can be controlled effectively within the speed range which is suitable for detection.The method to adjust the detector’s speed by adjusting the pressure difference has been studied deeply. As there are many parts inside of the detector, the discharge area covers only12%of cross-sectional area of the detector, thus it has very limited ability to adjust the detector’s speed. In this paper the detector’s running through the gas pipeline with having large diameter, high pressure, high-speed has been studied. Here, the main cause of the detector’s speed is analyzed. The detector’s speed is determined by the pressure difference of the pipeline which is the result to be obtained. Based on the gas pressure gradient the pressure-speed model of the detector is derived. According to the fluid mechanics, parameters of the model are determined. To make the model operable the model is refined by using the relationship of the total pressure, dynamic pressure, static pressure, and gauge pressure. Pressure velocity model validation is tested in the actual Gas Transmission Pipeline. Experimental results show that the model can calculate the detector’s speed in different pressure conditions. When the speed of the detector needs to be adjusted, the adjustment process can be regarded as the running speed of the particle running speed of a steady-state condition which will get changed to another steady state condition of the particle. The detector’s speed which is adjusted to the target speed requires up and down stream pressure and the pressure value can be calculated using the pressure-velocity model. By using the pressure value, parameters of the pipeline are changed to adjust the detector’s speed where the adjustment strategies are given. In Second West-East natural gas transmission project the pressure-velocity model is being verified. Experimental results show that the detector speed can adjust effectively by this model.The study of the detector’s controlling speed in the gas pipeline opens up the thinking that gas pipeline defects can not be detected by magnetic flux leakage testing, and makes a useful exploration work for developing Magnetic Flux leakage detection in Gas pipeline.