Research On Buckling Deformation Detection Technology Of Subsea Pipelines

Subsea pipelines are an important part of the subsea oil and gas transportation system.They are regarded as the lifeline of offshore oil and gas fields.In order to prevent crude oil from condensing,waxing and forming solid hydrates in a lowtemperature seabed environment,subsea pipeline is typically operated at high temperature and pressure with large axial and hoop stress.Due to the constraints of the pipe and soil,the axial stress is difficult to release through the elongation of the pipe,and is often released in the form of overall vertical or horizontal buckling,resulting in buckling deformation of the pipe.Subsea pipeline buckling can easily cause pipeline to break and accelerate pipeline corrosion and aging.Therefore,it is necessary to regularly and intensively detect the buckling deformation of subsea pipeline,so that people can timely take reinforcement and remedial measures.In the existing detection methods of subsea pipeline buckling deformation,the external detection method has high cost and long period,and the internal detection method is based on inertial navigation,has low sensitivity,and cannot independently navigate for a long distance in subsea pipeline.Considering that subsea pipeline buckling is not only accompanied with the local change of geometry and pipeline direction,but also has a special stress distribution,so the paper will with respect to these characteristics,carry out research on the theory and key technology of buckling deformation detection of subsea pipeline.The main work consists of three parts:(1)In order to determine the change of the pipeline direction by using the magnetic field in the pipeline,and then determine whether the pipeline is buckling,the magnetic shielding model of the pipeline containing non-ideal original magnetization is studied.By comparing the classical magnetic shielding model,finite element simulation analysis and experimental verification,it is demonstrated that the magnetic shielding coefficient of the field pipeline is statistically consistent with the infinitely long cylindrical cavity model,and the magnetic shielding coefficient does not change with the change of the pipeline direction.It can be used to predict the magnetic field distribution characteristics in the buckling and deformed pipeline,thus verifying the possibility of pipeline buckling magnetic characterization.(2)The distribution characteristics of the magnetic field in the buckling pipe are studied.According to its special stress distribution,the buckling deformation detection of pipeline based on magneto-mechanical effect is studied.The relationship between stress and relative permeability was calculated by the J-A force-magnetic coupling model.The finite element simulation analysis and experimental analysis for the buckling pipeline were carried out,and the finite element simulation coupled with multiple physical fields of thermal,force and magnetism.The results show that the small pipeline buckling deformation can be detected by using the magnetic field in the pipeline,which verifies the feasibility and advantage of the magnetic shielding effect and the magneto-mechanical effect in the application of pipeline buckling deformation detection.(3)For the change of pipeline geometry,a new method for vertical buckling detection of subsea pipeline based on spherical inner detector and magnetic proximity switch is proposed.This method determines whether the pipe has vertical buckling by measuring the pipe inclination in the high precision and high sensitivity.The feasibility and advantages of the method are verified by finite element simulation analysis and experimental verification,and most of the inclination measurement error is less than 0.5°.