Research On Internal Detection Of Buried Pipe Free Span

In order to make a pipeline transport oil and gas resources safely,stably and lastingly,the pipeline is often protected by burying it below the ground or seabed to a certain depth.As the service life of a buried pipe increases,due to manual operations,ocean current scouring,geological migration,or environmental load,a free span may appear along the buried pipe.The buried pipe free span may cause accidents such as pipeline damage,leakage or even breakage,which poses a great threat to pipeline safety.Therefore,the regular inspection of the free-span condition of a buried pipeline in service is of great significance to pipeline safety.Aiming at the problem of buried pipe free span detection,the theory,method and test research of the buried pipe free span detection under internal excitation load is studied in this paper.The specific content includes:(1)Aiming at the problem of the dynamic response of a buried pipe under an internal excitation load,a mathematical analysis model of the pipe-soil coupling system based on the three-dimensional elastic theory is established in the frequency-wavenumber domain.Based on the frequency response function,an algorithm for solving the dynamic response of the established mathematical analysis model is established.A systematic study of the influence of the pipe buried depth,the material parameters of the pipe and soil medium on the dynamic response characteristics of the buried pipe under an internal dynamic excitation load is carried out.Aiming at the problem of the dynamic response of a free-spanning pipe under an internal excitation load,a 3D finite element analysis model of a buried pipe-free span system based on ANSYS software is established.The influence law of the stiffness coefficient of the soil medium and the free span length on the dynamic response characteristics of the buried pipe-free span system under an internal dynamic excitation load is studied.The above studies provide a theoretical basis for the study of the buried pipe free span detection.(2)A signal preprocessing method and a signal analysis method for the buried pipe free span detection are established.A signal acquisition program based on Lab VIEW and a signal processing and analysis program based on MATLAB are established.Free span evaluation indexes based on frequency response function,resonance frequency change,resonance frequency change ratio,response signal energy and weighted response signal energy are established to analyze free span condition,calculate free span length and location.(3)A confirmatory test was conducted to validate the feasibility of the principle of the proposed method for the free span detection of buried pipe.Some key parameters in free span detection are analyzed.The free span section in a steel plate-soil system is used as a detection target.The equal-space fixed-point free span detection test and the mobile free span detection test were carried out respectively to study the influence law of the excitation signal sweep speed,excitation force amplitude and moving speed of the free span detector on the free span detection result.The free span evaluation indexes of the frequency response function,resonance frequency change and resonance frequency change ratio are used to calculate the length and location of a free span.The validity of the proposed free span evaluation indexes is verified.The above studies provide a basis for the study of the buried pipe free span detection.(4)A test apparatus used for detecting the free span of a buried pipe is designed and built.An equal-space fixed-point free span detection test is carried out to study the influence of the excitation signal sweep speed and excitation force amplitude parameters on the free span detection result.A mobile free span detection test is carried out to study the influence law of the moving speed of a free span detector on the free span detection result.The free span evaluation indexes of the frequency response function,response signal energy and weighted response signal energy are used to calculate the length and position of a free span.The sensitivity of the proposed free span evaluation indexes is verified.