Dynamic Analysis And Identification Technique Research For Cracked Pipe

Pipe plays an extremetly important role in the transport of petrochemical industry.Once an accident occurs will endanger the normal production, and even cause fire,explosion,poisoning and other accidents. There are many reasons contributing to thepipe damage, no matter the corrosion damage, fatigue damage,or brittle failure and soon,their eventually forms mostly are the cracks arise in the pipe and causing the failureof the pipe. In order to preventing form pipe accidents, finding pipe defect in time anddetermine the pipe position as accurately as possible has important significance toensure the social production, life and protect people’s lives. The nondestructive testingtechnology in present which apply to pipe system ubiquity have the shortcomings oflow efficiency, process trival, poor maneuverability and so on. The damage detectionmethod based on structural vibration overcome the above shortcomings and became anew method for pipe crack identification.The damage detection method based on structural vibration is through measurepipe structure to acquire vibration modal parameters of the system, and according thechange of structural modal parameter to identification the damage degree of pipe. In thestructural modal parameters, nature frequency is more easily to test than others, whichonly need to single point measurement by install a single sensor in the proper place, anddo not need to detection point by point when choosing measuring point. It’s easy tooperation and has high detection accuracy. Therefore, this paper studied the dynamic analysis and identification technique for craced pipe used damage detection methodbased on structural vibration, the main content includes:(1) Based on the strain energy release and the linear fracture mechanics principle,the equivalent stiffness equations of a pipe with a transverse crack whose tip directionwas at any angle with the vertical axis direction of pipe were derived, then therelationship between the crack parameters and the natural frequencies was obtained.Furthermore, the results of the first three order natural frequencies with different cracklocations, depths and angles were researched.(2) A experimental bench for pipe frequency measurements is designed, whichmakes it come true that the natural frequency of pipes with different pipe diameters,lengths and crack tip direction was at any angle with the vertical axis direction can bemeasured on the same test bench; The natural frequencies with different crack relativelocations, relative depths and direction angles was obtained by experimental results.furthermore, the nature frequencies’ change rule of at different work condition isalso discussed.(3) Based on the experiment of a pipe with a transverse crack, we received theexperiment test values and comparied it with the numerical solutions, the basicagreement between the two. It’s verified that the method to calculate numerical solutionof nature frequency is effectiveness, and sums up the crack in the pipe’s influence ruleto natural frequency of pipe.