Magnetic tomography method has been widely used for nondestructive external inspection of buried and submarine pipelines, which is based on the principle of metal magnetic memory to discern the danger level and location of the stress concentration zone by measuring the anomalies in the spatial magnetic field distribution outside the pipeline. The distribution characteristics and spatial propagation law of pipeline inspection signal detected by magnetic tomography method, the energy distribution and change law of spatial magnetic memory signal in the stress concentration zone of magnetized pipelines are studied in this paper. The magnetic dipole field is used to establish the magnetic field model in the stress concentration zone of the inner wall of the pipeline, and the magnetic energy and energy density of spatial magnetic memory signals under different lift?off values outside the pipeline are finite element calculated based on the magnetic energy theory to derive the distribution law of spatial magnetic field and the correlation of magnetic energy density of magnetic signals under different lift?off value is analyzed. The results show that the spatial magnetic field energy outside the pipe decays with the increase of lift?off value, and the decay is the fastest within the distance of 50 mm from the outer wall of the pipe to the physical force; the correlation of magnetic energy density of different lift?off values shows that the magnetic signal detected by magnetic tomography method outside the pipe is homologous with the signal in the stress concentration zone of the inner wall of the pipe. Theoretically, it explains the effectiveness of magnetic tomography method and also provides evaluation indexes for extracting effective signals from the detection data.

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.

In order to solve the problem that the angle of crack and magnetization direction was too small to identify in the pipeline magnetic flux leakage internal detection, the influence of crack angle on magnetic flux leakage detection signal and the characteristics of crack magnetic flux leakage signal under the condition of axial excitation of DC electromagnet were analyzed. Comsol finite element simulation software was used to simulate and analyze the crack defects of 0.2 mm in different angles of the inner wall of the pipeline. DC electromagnet axial excitation experimental platform was built, and EDM technology was used to process the specimens with different angles of crack to carry out the dragging experiment of the crack angle. Results show that the minimum detectable angle of crack and magnetization direction is 25°. The peak value of MFL signal decreases with the decrease of crack angle, larger the signal span, the greater the influence of noise signal. When the magnetization direction is perpendicular to the crack, the maximum span of MFL signal amplitude is the smallest, and when the magnetization direction is parallel to the crack, no MFL signal is generated.

In order to enhance the edge features of pipeline weld magnetic flux leakage image, an edge enhancement method based on Laplace and multi⁃scale mathematical morphology was proposed. Firstly, magnetic flux leakage data of pipeline magnetic flux leakage internal detector are collected for imaging, Then, using mathematical morphology algorithm, we construct multi⁃scale structural elements to detect the edge of the image, and use edge color constraints to delete non⁃edge points. Finally, edge is enhanced by Laplace operator. The results show that the method can accurately extract the weld and defect boundaries of the magnetic flux leakage signal image, and effectively separate the weld and defect. It has certain feasibility and practicability.

The adsorption characteristics of the alkaline nitride pyridine in simulated oil onto sixteen alkyl three methyl bromide(CTAB) modified SAPO-44 molecular sieve were studied. The effects of the amount of CTAB on the adsorption of basic nitrides on SAPO-44 zeolites were investigated. Moreover, the adsorption isotherms, kinetics and thermodynamics of the adsorption of alkaline nitrogen were studied. The results showed that when the amount of CTAB added was 0.06, the maximum equilibrium adsorption capacity reached 7.24 mg/g. The CTAB modified SAPO-44 molecular sieve has better adsorption efficiency when compared with the unmodified SAPO-44 molecular sieve. The adsorption isotherm of alkaline nitride on CTAB modified SAPO-44 molecular sieve is more in line with the Langmuir equation.The adsorption process accords with the pseudo second-order kinetic model, and the adsorption activation energy is 48.25 kJ/mol.