Total Focus Method Inspection And POD Analysis Of Austenitic Stainless Steel Welds

The butt joint quality of Austenitic stainless steel welding directly affects the safety of special equipment of bearing pressure,and it is easy to cause great loss of life and economy in case of accident.However,it is difficult to detect Austenitic stainless steel weld by conventional nondestructive testing because of the coarse grain size and obvious anisotropy.Compared with phased array ultrasound,the total focus imaging method has higher defect resolution and larger scanning coverage,and is widely used in the measurement and study of weld defects in Austenitic stainless steel,the reliability of its detection results has become the focus of attention of scholars.In this paper,the custom-made 90 mm thick weld Austenitic stainless steel and 20 mm thick typical weld Austenitic stainless steel are studied respectively,through the theoretical research,detection experiments and results analysis carried out related research.(1)An experimental comparison was made between phased array ultrasonic fan scanning,a commercial TFM imaging algorithm and an improved TFM imaging algorithm for Austenitic stainless steel thick weld specimens,the TFM imaging method can be used to characterize defects with an aperture of 1 mm in the internal weld zone of the Austenitic stainless steel,and to detect defects with a depth of more than 70 mm,compared to the traditional sector ultrasound imaging method,the standard deviation of the maximum amplitude of the 1mm defect in full-focus imaging was reduced from 9.22 d B to 3.48 d B,which is nearly twice the increase.The improved TFM imaging algorithm gain the good defect location result,and the location depth error is less than 2.2 mm.(2)Comparing the effect of TFM imaging with hard threshold de noising and soft threshold De noising on typical weld Austenitic stainless steel,the TFM imaging method based on soft threshold noising scheme is effective in detecting the length and depth of typical defects,the standard deviation of the depth and length of the upper and lower tip of the defect were 0.23 mm,0.60 mm and 0.56 mm,respectively.(3)Probability of detection(POD)is used to Quantitative analysis the detection rate of defects with different de-noising methods,based on the Signal response data model,the reliability of the detection results of the stainless steel deep weld holes with different depths is Quantitative analysis.At the same detection probability,the depth detected by the hard threshold de-noising TFM imaging method is larger than that detected by the improved TFM imaging method.The depth of soft threshold de-noising TFM imaging method is larger than that of hard threshold de-noising TFM imaging method.The detected depth of fusion zone and weld zone were 76.6 mm and 34.6 mm,respectively.