Research On Key Technologies Of Pipeline Defect Monitoring Based On Guided Wave B-Scan Imaging

With the rapid development of China's economy,pipeline transportation takes its advantages of small land occupation,large transportation volume and low cost as the main mode of transportation of oil,gas and other energy resources.Its construction scale is also growing,and it has achieved remarkable achievements.Pipeline transportation is not only related to the economic lifeline of the country,but also related to the safety of public life and property.With the increase in the service life of some in-service pipelines,it is inevitable that there will be losses.In the event of an accident,it will cause immeasurable losses to public life and property.In addition,due to the large scale and complicated structure of the pipeline system,the traditional point-by-point nondestructive testing technology is time-consuming and laborious,and difficult to implement,especially in some inaccessible places.Ultrasonic guided wave has been gradually applied to the detection and monitoring of pipelines due to its application advantages such as single-point excitation and long-distance propagation,and has become one of the most potential non-destructive testing technologies and structural health monitoring technologies.At present,the guided wave mode used to detect pipelines in industry is the T(0,1)mode,which is loaded in the way of full circumferential coverage.It has the advantage of easy excitation,no dispersion and easy to locate defects in the axial direction.However,this full circumferential coverage method lacks the circumferential positioning capability for defects in practical applications,and it is difficult to identify small defects that are submerged by the inherent characteristic signals of the pipeline(such as the welding bracket signal).There are blind detection areas in pipeline welding brackets and tees of different sizes,and in the actual working condition,welding bracket position is easy to accumulate water and accumulate salt,which is more prone to have defects.Moreover,with the increase of the diameter of the pipeline,the sound power density per unit area becomes smaller,and the defect sensitivity becomes more and more insufficient,which is not suitable for the detection of large diameter pipelines.In addition,because the T(0,1)modal guided wave of the full circumference coverage mode only carries the axial information,the pipeline is usually characterized by one-dimensional A-scan signal,which is not intuitive in the signal and can not visualize the pipeline panoramic information.In addition,the detection method often lead to blind excavation,blind scrap,and lack of scientific maintenance,resulting in a great waste of manpower,material resources and financial resources.Therefore,it is urgent to develop an economical and effective structural health monitoring technology to monitor pipelines in service.Therefore,the research object of this paper is ultrasonic guided wave pipeline defect monitoring technology,and the starting point is how to use limited monitoring equipment to solve practical application problems more effectively,which is supported by the National Key Research and Development Program of China(2018YFC0809002).Firstly,in order to make up for the shortcomings of the T(0,1)detection method,the B-scan imaging of pipeline based on ultrasonic guided wave circumferential scanning is proposed and is carried out to analyze its technical advantages and practical value.Secondly,the theory of pipeline guided wave propagation based on local wave source loading is studied,the application research of guided wave imaging technology and image processing algorithm is mainly carried out.Then,the influence factors of guided wave diffusion length under local excitation load and the improvement of scanning circumferential resolution by synthetic aperture focusing are obtained through experiments.Finally,a set of ultrasonic guided wave pipeline defect monitoring experimental system is built,and its overall framework and key technologies of each part are described in detail.Specific research work includes:In chapter 1,aiming at the urgent need of pipeline health monitoring,the technical pain points and challenges faced by T(0,1)modal guided wave with full circumference coverage are indicated,and the research direction is pointed out.The technical advantages and practical value of pipeline B-scan imaging monitoring are expounded,and the research status at home and abroad is analyzed.At the same time,the research content and organizational structure of the paper are pointed out.In chapter 2,the theory of pipeline guided wave propagation based on local wave source loading is studied,and the guided wave source is analyzed by the normal modal expansion method.The principle of B-scan imaging of pipeline and the problem of circumferential resolution of imaging affected by guided wave sound beam diffusion are expounded.And the theoretical study on improving the circumferential resolution by using synthetic aperture focusing is carried out.In chapter 3,the influence factors of monitoring are analyzed and the algorithm is designed for preprocessing.The steps of establishing a complete and adaptive reference signal bank are elaborated.An image monitoring algorithm which can automatically extract defect features and locate defects is designed.In chapter 4,the effects of guided wave beam diffusion and the improvement of synthetic aperture focusing are experimentally studied.The experiments compare the effects of full circumference coverage mode and circumferential scanning,highlight the advantages of scanning monitoring,and prove the feasibility of image monitoring algorithm.In chapter 5,an experimental system of ultrasonic guided wave pipeline defect monitoring based on B/S architecture is successfully built.The overall framework and key technologies of each part are described in detail.In chapter 6,summary and prospect.The research achievements of this paper are summarized,and the future research work are forecasted.