Pipeline In-line Inspection Method And Multi-parameter Evaluation Based On Eddy Current Testing

Pipeline transportation is one of the five major transportation industries,along with railways,highways,aviation,and water transportation,and has become the lifeline of modern industry and the national economy.Internal inspection of defects and damages in oil and gas pipelines is an important and urgent means in the field of modern oil and gas pipeline operation and maintenance.However,the current mainstream internal inspection methods have limitations,including limited feature extraction and unsuitability for gathering pipelines’ inspection.Electromagnetic eddy current internal inspection method has advantages such as non-contact,no need for coupling agents,no need for magnetic saturation,sensitivity to multiple parameters,and ease of integration,making it suitable for use in this application scenario.However,this technology still faces challenges:Firstly,electromagnetic eddy current inspection is susceptible to lift-off effects,where complex surface conditions can seriously interfere with the detection signal-to-noise ratio and detection rate of defects.Secondly,it is challenging to distinguish between lift-off and defect signals based on electromagnetic eddy current signals,which affects defect discrimination and quantification accuracy.Finally,specific probe designs are only effective for detecting certain types of defects,and the detection capabilities for multiple types of defects on the inner wall of the pipeline need improvement.In response to the above-mentioned issues,this dissertation has conducted research on electromagnetic eddy current method for pipeline in-line inspection.The critical factors affecting eddy current defect detection performance were analyzed based on theory of harmonic electromagnetic fields and electromagnetic induction principles.The relationship between the probe design and parameter evaluation of eddy current testing under lift-off influence was investigated.Additionally,a differential-mode coil with dual conditioning circuit platform was built for multi-parameter measurements to address the issue of lift-off effects on signal-to-noise ratio and defect detection rate.Furthermore,the common-differential mode coils for separation of lift-off and defect signals based on the dual conditioning circuit system was proposed.The detection and evaluation of different types of defects have been performed through the robotic arm dynamic scanning system and the independent development of the pipeline internal inspection system.The main research work and innovation points of the dissertation are as follows:1.This dissertation focuses on the application scenario of pipeline eddy current internal detection and analyzes the lift-off effect that affects the performance of pipeline defect detection based on the theory of time-harmonic electromagnetic fields and electromagnetic induction.Building on the basic principles and research methods of eddy current detection,we study the relationship between eddy current sensor design and parameter evaluation.Through numerical simulations and theoretical analysis,we examine the relationship between the eddy current coil structure and magnetic field distribution,as well as the interplay between lift-off and conditioning circuits,defects,and conditioning.This research provides a theoretical foundation for addressing lift-off issues and enhancing the detection of multiple types of defects in the future.2.To address the issues of low signal-to-noise ratio and low detection rate caused by lift-off effects during pipeline inspection,dual-channel differential probe composed of an AC bridge and a transformer-based conditioning circuit structure was proposed.Through numerical simulations,the factors affecting coil sensitivity were investigated.Utilizing an equivalent circuit model,the relationship between the amplitude,phase parameters,and lift-off for each channel of the dual-differential detection system in the alternating magnetic field was established.By observing complementary variations in output amplitudes of the differential coils in response to lift-off effects on the AC bridge and transformer conditioning circuits,a multi-parameter amplitude-phase signal fusion method is introduced.A dual-conditioning circuit detection system was developed and tested,validating the effectiveness of the multi-parameter lift-off suppression method.This approach enhances sensitivity and detection capability.3.To address the issue of lift-off interference in the identification and quantification of pipeline defects,an innovative approach was introduced.Building upon the foundation of the dual-conditioning circuit multi-parameter measurement system,coil configuration was designed to modify the distribution of the magnetic field.This involves the introduction of a sensing structure that combines common-mode and differential-mode elements.The relationship between the common-mode coil’s bridge output amplitude and lift-off within the AC bridge conditioning circuit architecture is investigated.Additionally,the relationship between the differential-mode coil’s amplitude and defect perturbations under the transformer conditioning circuit architecture is explored.Leveraging the characteristics where common-mode coil output is sensitive only to lift-off and differential-mode coil output is sensitive only to defects,a combined hardware and software measurement method is developed.By decomposing amplitude and phase components,the method successfully separates and estimates lift-off and defect information.The isolated lift-off information aids in defect discrimination and quantification,enhancing the overall ability to identify and quantify defects.4.For the detection of multiple types of defects during pipeline internal inspection,this approach leverages the relationship between conditioning circuits and complementary directional defect measurements as explained in 1.Specifically,the bridge circuit is sensitive to circumferential defects,while the transformer output is sensitive to axial defects.Building upon the dual conditioning circuit system and dual coil sensing architecture proposed in 2 and 3,a pipeline multi-parameter array internal instrument was developed.In the laboratory,verification tests for multi-type defect detection and discrimination are conducted using different types of specimens,including flat plate defect specimens,half-pipe defect specimens,and pulled pipelines.The results demonstrate that the developed multi-parameter array internal detection system has the capability to detect various types of defects effectively.It can reliably identify welding seams,volumetric corrosion defects,and crack defects.The research presented above has addressed the challenges related to lift-off and the detection of multiple types of defects in pipeline electromagnetic eddy current internal inspection technology.The integration of coil structure design and conditioning circuit systems enables multi-parameter measurements.This approach allows for multiparameter fusion to suppress lift-off effects and multi-parameter separation for defect identification and characterization.Consequently,it enhances the ability to detect and discriminate various types of defects in pipeline internal inspection.These findings provide a robust foundation for the subsequent development of electromagnetic eddy current internal inspection system instruments for pipelines and establish a practical framework for the application of future pipeline internal inspection technologies.