Research On Measurement Technology Of Digital Radiography Flaw In Small Diameter Tube Weld

With the continuous development of industrial technology,small diameter tubes are used more and more widely;however,safety accidents makes people put forward higher requirements for the safe use of small diameter tube.Most of the small diameter tubes are welded,including small diameter tube with other components.Flaw are easily to be founded due to improper welding methods or ircorrect welding parameters.Radiographic testing,as the main technology of non-destructive testing technology of small diameter tube,has unique advantages in flaw characterization,but it is difficult to measure the size of flaw along the direction of ray penetration,so it is impossible to realize the all around testing and evaluation of flaw.In order to effectively prevent safety accidents caused by welding flaw effectively and improve the service life of small diameter tubes,this paper puts forward a research topic based on x-ray digital radiography on the accurate measurement of weld in small diameter tube,and conducts experimental design and analysis on the subject.The main research contents of this paper are as follows:(1)The choice of testing system.The radiographic testing-film and digital radiography comparison experimental scheme is designed,a number of small diameter tube welds containing different types of flaw are customized,based on the existing laboratory testing system,from the point of view of image quality and flaw testing rate,radiographic testing-film and x-ray digital radiography comparison research is carried out to determine the x-ray digital radiography testing system suitable for small diameter tube welds.(2)The theoretical analysis and experimental research based on the penetration thickness-image gray model based on the experimental data.Based on the theory of x-ray digital radiography,the relationship between image gray and penetration process conditions,line attenuation coefficient and penetration thickness is explored,and a model of image gray-penetration thickness is established.And on the basis of theoretical derivation,the penetration thickness-image grayscale model parameters are perfected based on the selected x-ray digital radiography testing system based on different known thickness steel test blocks.(3)Flaw size measurement accuracy study.Based on the complete model of gray-penetration thickness of the above image,the x-ray digital radiography experiment was carried out under specific process conditions to verify the accuracy of the model by taking the steel step test block with known thickness and the small diameter tube hole at known depth as the penetration object respectively.The results show that the error range of steel step test block is 0.11%to 2.02%,and the calculation error range of small diameter tube hole is 0.29%to 8.77%.(4)Experimental verification of flaw size measurement.Using a specific penetration process to carry out x-ray digital radiography and CT experiments on the small diameter tube weld,reading the maximum gray of flaw in x-ray digital radiography images,replacing the model to calculate the maximum size of flaw along the direction of ray penetration,collecting image reconstruction slices for CT experiments,measuring the maximum size of flaw along the direction of ray penetration,comparing the errors between the two.The results show that the flaw measured by the model have a margin of error of 3.40%-9.07%along the dimensions of the ray penetration direction and the flaw measured by CT in the direction of ray penetration.Through the research of this paper,a new method of accurate measurement of flaw along the direction of ray penetration by smal diameter tube welds can be proposed,which can be calculated directly according to the actual penetration process conditions and image gray,and then combined with x-ray digital radiography image measurements perpendicular to the flaw dimensions in the direction of rays,and the three-dimensional information of flaw can be obtained to evaluate flaw in all directions.The research results solve the problem of measuring the height of flaw along the direction of ray penetration,lay the foundation for correct assessment of flaw,correctly check safety hazards in time,and avoid unnecessary property damage and casualties.