| Inner Inspection PIG is a kind of effective equipment which was used to test the gas and oil pipeline. As the West-East natural gas pipeline and the Sichuan-East gas pipeline are put into service, the safety of our gas pipelines has become a significant issue which impact national economy and people's livelihood, so it is very important to study the Inner Inspection PIG. Because of the compressibility and aridity of the gas, the steady motion and optional magnetic circuit are the keys to meet the need of inspection precision. The dissertation begins with the two critical items mentioned above, and studies the main parts of Inner Inspection PIG such as drive system and inspection system on theory and experiment. The dynamic equations of different drive cups in various pipeline have been establish , the model test bed of move device has been created , the system of smart PIG has been designed and optimized .The site simulant experiment system has been built, and the prototype of Inner Inspection PIG has been tested .The following has been got through the research:It is feasible to inspect the defect of gas pipeline by the technology of magnetic flux leakage. Through analyzing formation mechanism and signals character of defects, detecting system in dry and high pressure gas environment has been studied and designed, the internal and external defects identification has been solved. The lift-off of magnetizer and sensor has been chosen and verified.It studies on the theoretical discussion and numerical simulation on circumferential MFL technology and puts forward the identification and modification method of defects signals in non-uniform magnetic field. The technology can detect the defects which diameter is more than 2mm and depth is more than 1.5mm or diameter more than 3mm and depth more than 1mm and it can fit the need of the gas pipeline inspection. It proposes and verifies the optimal detection in terval of velocity.The relevance ratio drops with the speed of Inner Inspection PIG raising, and when the speed is more than 4m/s the relevance rate will drop dramatically. Controlling the speed is a key to get an effective detection when we inspect the gas pipelines.The motion and dynamics analysis model of driver cups with different structure has been created ,the relationship of the cups structure ,which including common drive cup, elastic bottom cup and umbrellashaped dirve cup, difference in pressure and the moving state of driver has been researched. The conclusions are: when common cup and elastic bottom cup move in level pipeline, the lip structure of cup, material and obstruct in pipeline are the major factors which affect the steady motion of Inner Inspection PIG. In undulant pipeline, the length of cantilever beam of cup lip affect the steady motion of Inner Inspection PIG significantly. If the stiffness, driving pressure and the length of cantilever beam of cup lip are unchanged, Inner Inspection PIG can move steadily in level pipelines , but it is hardly to complete the steadily movement in undulant pipeline . By improving the structure of the driver lip and the stiffness of the bottom, Inner Inspection PIG can moves steadily in limited undulant pipeline and certain different pressure .If the new umbrellashaped cup, which can change its stiffness is used, Inner Inspection PIG can move steadily in more undulant pipeline. The test bed, which could be used in simulatiom experiments has been designed and built.The gas pipeline prototype,namedФ1016 inner inspection PIG has been manufactured and several site simulation experiments have been done. The site experiments results show that velocity control is the key in gas pipeline inspection.The speed can be controlled in 20 degree fluctuation pipeline by changing the structure of driver cup. And BIG can move steadily in 20 degree fluctuation pipeline. A certain quantitative relation between defects and MFL signails has been verified.The simulation experiments also show that it is feasible to identify the internal and externail defects, and there is relationship between velocity and relevance ratio, the reasonableness in magnetic circuit design. Theoretical basis and designing template have been given on designing inner inspection in gas pipeline.
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