Study On Ultrasonic Measurement Influencing Factors Of Pipe Wall Thickness

As a key part of the core equipment in aerospace,national defense,petrochemical and other fields,the accuracy of pipes wall thickness is required to be high in engineering applications.Ultrasonic thickness measurement technology has the advantages of strong applicability,high measurement accuracy and good safety.It is widely used in the rapid and high precision measurement of pipes.But the accurate measurement of workpieces wall thickness by ultrasonic thickness measurement is affected by many factors.Therefore,based on the propagation characteristics of ultrasonic waves in the pipes,the thesis analyzed the propagation paths and scattering of acoustic waves.And the two problems which probe eccentricity generates the incidence deflection angle to cause the thickness measurement error and surfaces roughness generates scattering waves to cause flight-time extraction error were deeply studied.The thickness measurement error is caused by the deflection angle between the center line of the ultrasonic probe beam and the normal line of the measured surface.In this thesis,the propagation paths of acoustic waves in steel pipe and steel plate under different deflection angles were analyzed.The propagation process of acoustic waves in the range of0-2° was simulated by finite element analysis.The variation rule of echo signal under different incidence deflection angles was obtained,and the curve of thickness measurement error with deflection angle was fitted.The results show that the accuracy loss of θ≥1° is obvious,and the thickness measurement error caused by measuring the steel pipe is0.12 mm when the deflection angle is 2°.The ultrasonic thickness measurement experiments were carried out on steel plates and steel pipes.The experimental results were compared with the simulation,and the trend was consistent.Aiming at the thickness measurement error caused by the deflection angle,the error compensation model was established.The results show that the thickness measurement accuracy of the pipes under different incidence deflection angles is effectively improved,and the measuring error of the compensated pipes can be reduced by up to 53% in the angle range of 0-0.5°.In order to reduce the error caused by the deflection angle,the probe positioning V-block was designed.The pipe with R=100mm and D=4.971 mm was measured,and the measurement error was less than the error caused by the deviation angle θ=0.1°.Based on the theory of phase screen approximation,the scattering characteristics of acoustic waves on rough surfaces were studied.The transmission coefficient and reflection coefficient of acoustic waves considering the surface roughness of the workpiece were derived.The relationship between the root mean square deviation of the surface micro profile and the amplitude of the echo was obtained.The influence of surface roughness on the echo signal was analyzed by the finite element method,and the attenuation rule of the echo signal with the change of roughness was obtained.Finally,ultrasonic thickness measurement experiments were carried out on pipes with different surface roughness values.The correctness of the theoretical analysis was verified by experiments.The ultrasonic measurement thickness errors under different roughness values were quantified.Finally,the comprehensive influence of workpiece surface roughness and deflection angle on the thickness measurement accuracy was analyzed.And the influence rule of roughness on the pipe wall thickness measurement results under the condition of deflection angle was obtained.