Non-destructive Testing Of Elbow Erosion Based On Infrared Technology And Identification Of Inner Boundary Of Pipeline Defects

Industrial pipelines are important transportation equipment and pressure vessels.For elbows,erosion and corrosion at the inner wall of the elbow is the main reason for its leakage failure.Without affecting the normal operation of the pipeline system,accurate detection of internal defects is a necessary prerequisite for ensuring the safe operation of the pipeline.Infrared non-destructive testing technology is simple and fast,and can effectively find internal defects of objects,so it has become one of the important non-destructive testing methods.In this thesis,a non-destructive testing simulation based on the pulse thermal method is carried out for the erosion defect of the elbow,and the influence of the erosion degree,the pipe material and the fluid is studied respectively.Studies have shown that for common water pipelines,when using three different pipe materials:brass,stainless steel and low carbon steel,the temperature distribution of the erosion zone at the valley of the temperature difference in the cooling phase is clearer than the temperature distribution of the erosion zone at the peak of the temperature difference in the heating phase.Therefore,for water pipelines,the temperature distribution of the valley of the temperature difference can be used as the basis for diagnosing defects.For low-carbon steel pipes,when transporting high-viscosity fluids such as oils,the contour of the erosion zone at the peak temperature difference during heating is clearer than the contour at the valley value of the temperature difference during cooling.The temperature distribution at the peak of the temperature difference can be used as the basis for the diagnosis of defects in the elbow for transporting high-viscosity fluidsWhen the temperature difference is small and the accuracy of the thermal imager is low,using the pulse thermal imaging method for detection,the contrast between the defective area and the non-defective area is low,and the contour of the erosion area is blurred.This article uses modulated thermal imaging method for non-destructive testing simulation,focusing on the phase information between defects and non-defect areas.In this paper,the influence of erosion degree,pipe wall material and fluid has been studied.For water pipelines,the maximum phase difference and optimal modulation frequency increase with the increase of erosion degree and pipe thermal diffusivity.For high-viscosity fluids,as the fluid viscosity increases,the maximum phase difference increases and the optimal modulation frequency decreases.In addition to diagnosing defects in engineering,sometimes it is necessary to quantitatively analyze the shape and size of the defect.Therefore,it is necessary to find a way to identify the shape of the defect.In this paper,the conjugate gradient method is used to inversely identify the inner wall of the pipeline defect.The effects of inversion parameter settings such as the number of temperature measurement points and the number of inversion nodes,as well as heat transfer factors such as convection heat transfer coefficient and tube wall material,on the geometric inversion results are studied.The inversion results show that the inversion accuracy increases with the increase of the number of temperature measurement points and the number of inversion nodes,the decrease of the convective heat transfer coefficient,the thermal diffusivity and thermal conductivity of the tube wall material,and the increase of the heat flux density.The inversion result is less sensitive to the standard deviation of temperature measurement.When the number of temperature measurement points is not less than 12,the number of inversion nodes is not less than 36,the convective heat transfer coefficient is less than 1000W/(m2·K),and the heat flux density is greater than 2000W/m2,for common steel materials,the geometric mean error obtained from the inversion is less than 3.34%.