Measuremen Of Erosion And Corrosion Defects In Pipeline Inner Wall Using Ultrasonic Doppler Velocity Profiler

Erosion corrosion is widely found in process industrial equipment such as energy,chemical,petrochemical,nuclear and environmental engineering.Process industry equipment includes condenser,fluidized bed burner,turbine and etc.However,due to the lack of detection of erosion corrosion defects,accidents occur often happens.Therefore,the detection of erosion corrosion defects in pipelines is particularly important.The Ultrasonic Doppler Velocity Profiler(hereinafter referred to as UVP)is a new detection method applied to the corrosion defects of the inner wall of the pipeline.The advantages of this method are too more,such as wide applicability of the tube wall materials,unlimited kinds of fluid in the test tube and non-intrusive measurement without affecting production.There are few studies on the application of UVP in flow measurement and erosion corrosion of pipeline inner wall.Considering the problems in UVP reality detection,this paper mainly does the following research:Firstly,this paper is based on the wave equation of acoustic waves,using the boundary conditions of continuous displacement and stress of ultrasonic waves on the interfaces of various media.According to the physical model of acoustic wave propagation in water-pipe wall-water three-layer medium,a mathematical model containing the product of frequency thickness(the product of detection frequency and the thickness of pipe wall),the transmission coefficient and the incidence angle is established.By numerically simulating the change of the transmission coefficient of the ultrasonic wave at different incident angles,the following laws are found: First,the transmission coefficient is larger when the incident angle is at 40 to 60 degrees.Except for the area near the first critical angle of 33.24 degrees(the first critical angle is calculated according to Snell law),the transmission coefficient and frequency thickness product of other areas change periodically.Second,as the thickness of the tube wall increases,the range of larger transmission coefficients gradually decreases,making it more difficult for sound waves to pass through the tube wall of larger thickness.In contrast,thinner tube walls make it easier for sound waves to penetrate,and it is easier to obtain the optimal angle of incidence.Furthermore,an experimental device for UVP water circulation is designed and built.The final optimal angle of incidence is determined through UVP flow error experiments.The UVP flow error experiments found the following laws: When the wall thickness of the pipe is 5 mm,the flow error obtained with 5 degrees incidence is larger,and the flow error when the incidence angle with 10 degrees is smaller,and the flow error is more dispersed and larger when the incident angle is 15 degrees,20 degrees,25 degrees and 30 degrees.when the incident angle is 35 degrees,it is near the first critical angle(the first critical angle is calculated as 33.24 degrees according to Snell law),the flow error continues to increase.The flow error is also small when the incident angle is 40 degrees,45 degrees and 50 degrees.The experimental conclusion of the flow error that the 1mm pipe wall is similar to the 5mm pipe wall.At the same time,the flow error obtained when the thickness of the pipe is 1 mm is significantly smaller than the flow error of the thickness of 5 mm,the main reason is that the thick tube wall causes a larger range of transmission coefficient to become smaller.It is found that the minimum flow error is less than 1% at 10 degrees.Combining the numerical simulation and the UVP flow error experiment,the optimal incident angle of subsequent experiments is finally determined to be 10 degrees.In addition,the flow values at different circumferential angles are studied,and the error values of the multiple circumferential angles are compared.The flow error values at different circumferential angles are quite different and the flow value errors obtained from a single speed distribution are all large.The flow accuracy obtained by interpolating the flow values at multiple measurement positions in the circumferential direction is significantly improved.The experimental conclusion provided a theoretical basis for accurate measurement of pipeline flow using UVP method.Finally,the CFD numerical simulation and UVP experiments are used to analyze the fluid state in the pipeline under different Reynolds numbers and different defects.The following conclusions are obtained: First,a comparative analysis of the changes in the fluid velocity distribution near the critical point of the defect in the pipeline shows that eddy currents would occur near the wall of the critical defect.When the defect size of the wall is the same,as the Reynolds number increases,the vortex phenomenon becomes more obvious.At the same Reynolds number,the eddy current will be larger when the defect is larger.Second,by comparing the changes in the fluid velocity distribution at the defective and non-defective pipeline,the fluid velocity distribution section at the pipeline defect is larger than the fluid velocity distribution section at the non-defective pipeline.The erosion and corrosion degree of the pipe wall can be further judged using this law.These conclusions provide a theoretical basis for UVP measurement of erosion and corrosion defects on the inner wall of fluid pipelines.