The fracture damage of oil and gas pipelines usually initiates from micro?cracks. The weak magnetic detection method is of practical significance for the detection of microcracks in long distance oil and gas pipelines. However, the microstructure of pipeline microcracks is complex, and the traditional weak magnetic field detection model is difficult to achieve accurate quantitative calculation of pipeline microcracks. Based on the theory of magnetoelectric coupling, a mathematical model of weak magnetic signal of pipeline micro?crack is established. The weak magnetic signal of micro?crack under different excitation conditions is compared and analyzed. The propagation characteristics of micro?crack at different depths and the signal detection characteristics under different lifting values are analyzed and calculated. The results show that the weak magnetic signal generated by the microcrack is much larger than the geomagnetic field, and the difference increases as the increase of the stress value. The weak magnetic signal increases with the increase of stress value. When the critical point of microcrack propagation is reached, the magnetic energy is released due to microcrack propagation, and the weak magnetic signal decreases with the increase of stress value. After microcrack propagation, the magnetic sensitivity of the material decreases, but the linear characteristics are more obvious. The larger the crack depth is, the stronger the weak magnetic signal is, and the damage is more easily detected. With the increase of the lift value, the weak magnetic signal decreases exponentially, and the detection accuracy of the signal in the linear region is the highest.

In the multiphase flow pipeline transportation system， in the process of hydrate slurry flow， rugged terrain will be encountered. At this time， the use of inclined pipeline is particularly important. Therefore， the influence of the flow characteristics of gas hydrate slurry in the inclined pipe on the blocked pipeline was studied. The hydrate plugging experiment of oil + natural gas in oil?based system was carried out on the low?temperature and high?pressure visual hydrate experimental loop， and the effects of initial pressure， initial flow and other factors on the flow and plugging time of natural gas hydrate slurry were explored. At the same time， the micro changes of hydrate particles in the process of hydrate formation， flow and pipe plugging were analyzed by real?time online particle tester. The experimental results show that with the increase of initial pressure， the induction time， formation time and slurry flow time of natural gas hydrate are shortened， and the pipe plugging trend of natural gas hydrate increases. With the increase of initial flow rate， the induction time， formation time and slurry flow time of natural gas hydrate are prolonged， and the pipe plugging trend of natural gas hydrate is reduced. Finally， the process from hydrate formation to pipe plugging and the plugging mechanism were analyzed. The research results of gas hydrate plugging pipelines in oil?based systems show that the probability of gas hydrates blocking pipelines can be effectively reduced by reducing initial pressure and increasing initial flow rates in oil?based systems. The research results can provide theoretical reference and basis for maintaining and ensuring the safe flow of natural gas hydrate in pipelines.

With the development of artificial intelligence technology and big data Internet technology, the pipeline leak detection technology is developing in the direction of intelligence. Based on the classification of continuous pipeline leak detection technology and discontinuous pipeline leak detection technology, this paper introduced the principles of various leak detection methods, summarized and analyzed the research status of long?distance oil pipeline leak detection technology at home and abroad. The application of combined oil pipeline leak detection and location technology in long?distance oil pipeline detection was prospected.

The weak magnetic stress detection technology supports non?contact online detection of stress damage. It has great application potential in the field of long?distance oil and gas pipeline stress detection technology. However, as the weak magnetic signal is weak and easy to be interfered by the external environment,the detection result is prone to deviation.In order to strengthen the detection ability of weak magnetic signals, based on the microscopic characteristics of ferromagnetic materials, a weak magnetic stress detection model under an external magnetic field was established, and the change law of weak magnetic signal strength with the increase of external magnetic field strength and applied stress was obtained.The excitation characteristics of the external magnetic field to the weak magnetic stress detection signal were described,and a systematic experimental study was conductd.The results show that the tangential peak value and the normal zero point of the weak magnetic signal are located in the center of the stress concentration area, and do not fluctuate with the change of the stress and the external magnetic field.The tangential peak value and the normal peak?peak of the weak magnetic signal increase with the increase of the external magnetic field and stress. As the external magnetic field increases, the excitation effect of the external magnetic field on the weak magnetic stress detection signal increases first and then decreases.

The residual magnetic stress detection technology can effectively detect the stress concentration of ferromagnetic materials, and has great potential in the field of long?distance oil and gas pipeline stress detection. However, due to the imperfect mechanism of the residual magnetic stress detection technology, the relationship between the residual magnetic signal and the stress is difficult to calculate quantitatively, resulting in the quantitative measurement of the residual magnetic stress detection, which seriously affects the application of the technology in the field of pipeline detection. In this paper, the mechanism of remanence generation is explained based on the magnetic domain model. Correspondence between remanence and stress is established by coercive force. The changing characteristics of remanence signal with the change of stress are analyzed and verified by experiments. The research results show that the irreversible magnetization of ferromagnetic materials is the cause of residual magnetism; as the external stress increases, the residual magnetism signal has a gradually increasing change rule.