Research On Non-destructive Testing Method For Non-metallic Pipes Based On Microwave Imaging

In recent years,as one of the five major transportation industries,pipeline transportation has played a huge role in national economy and modern industry with its unique advantages.Among them,non-metallic materials are widely used in oil and gas transportation and other fields due to their advantages such as corrosion resistance,good thermal insulation,and low inner surface roughness.However,in actual production,transportation and construction and installation,non-metallic pipelines will have various defects,which will greatly affect the structural integrity and safety of the material and even pose a great threat to public life safety.Therefore,the use of non-destructive testing technology to inspect and evaluate the quality of non-metallic pipelines to ensure their integrity is an important part of the manufacturing and service process.Compared with conventional NDT techniques,microwave NDT has the advantages of non-contact,strong penetration,high image contrast and fast real-time,and has gained wide attention in recent years.Based on the characteristics of microwave NDT,it is of great significance to carry out the research of non-metallic pipeline NDT with microwave imaging.Based on microwave reflection theory and signal processing technology,this paper focuses on microwave near-field imaging for nondestructive testing of non-metallic pipes.Based on the basic principles of microwave near-field imaging,we analyze several models and related criteria for planar scan data acquisition,construct a two-dimensional imaging model and method,and experimentally verify the near-field two-dimensional imaging algorithm.Image post-processing is performed for the imaging results to highlight the defect characteristics and to quantitatively characterize the defects.The main research is as follows:(1)A geometric model for planar scan imaging detection is established,and the scan interval selection,sampling criterion,and resolution are analyzed.On this basis,a cluttersuppressed target feature imaging enhancement method is proposed,which firstly suppresses the strong clutter of the echo signal by principal component analysis,and secondly performs two-dimensional imaging using wave spectrum reconstruction to achieve imaging enhancement.An experimental platform is built to obtain the measured data to verify the effectiveness of the proposed method.The results show that the proposed method can effectively image defective targets,and its imaging quality is better than that without clutter suppression.(2)Microwave image processing and quantitative defect characterization methods were studied.Firstly,the image was filtered for noise reduction and defect enhancement;then the extraction algorithm of non-metallic pipe defects was designed,using threshold segmentation and edge extraction to highlight the defect features,while the number,location and size of defects and other information were discriminated.The imaging results of the previous section were processed using this method and compared with the theoretical values,the localization error of defects was 2.38 mm and the average value of the relative error of area quantification was 13.25%.(3)A microwave imaging non-metallic pipe defect detection and identification software system was developed,using MATLAB tools to integrate the microwave imaging detection method studied in this paper and to write the GUI interface.The software can read the test data,perform imaging processing and image post-processing,display the imaging results and quantitative characterization results,and provide convenience for users to characterize nonmetallic pipe defects effectively in real time.