:Pipeline inner inspection technology based on pipeline inspection gauge (PIG), is the primary means to ensure the safety and reasonable maintenance of oil and gas pipelines. Aiming at the problem of sudden changes in dynamic behavior of the PIG when impacting the girth weld in the pipe under the action of high-pressure fluid. A dynamic model of the sealing disc based on Kelvin spring damping in the circumferentially confined space is established. The PIG system dynamics model is established based on the sealing disc model. The axial vibration differential equations of the overall model and the flow equation are deduced in detail. The fluid-solid coupling simulation of Matlab/Simulink and Adams is carried out. The dynamic response of the PIG to impact the girth weld is studied when the velocity of motion is changed. The results show that the established dynamic model of the sealing disc and pipeline PIG system can well characterize the mechanical properties of the sealing disc and the PIG in the axial, radial and circumferential directions of the pipeline. The faster the PIG moves, the more intense the axial vibration caused by the girth weld, and the more obvious the collision vibration, while the vertical and the pitch vibrations are significantly weakened with the increase of the moving velocity.
Subsea pipeline is crucial for oil and gas transportation. It is advantageous to be able to identify the free-spanning segments of a long subsea pipeline. The existing technologies for detecting the support condition of buried subsea pipelines are constantly affected by complex external environment since they are outer pipeline detecting methods. An inner pipeline method for detecting the support conditions of buried gas subsea pipelines based on forced vibration signal analysis is proposed in this study. Two evaluation indicators, frequency response function and natural frequency change ratio, are used to identify the free-spanning segments. A free span-detecting device and a test rig are built to verify the applicability of the method by forced vibration tests. Gray contour plots of frequency response functions and natural frequency change ratio bar charts are generated to analyze the experimental results. The experimental results show that two evaluation indicators are sensitive to the support condition. The appearance of the free span and its length can be identified by the gray contour plots of frequency response functions and natural frequency change ratio bar chart.
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