Large gas turbine stainless steel casings have large dimensions and complex casting proces-ses,which are prone to defects such as microcracks,air holes,and inclusions during the casting process.Due to the large thickness of the casting,conventional radiographic testing techniques are difficult to penetrate and inspect the large wall thickness casting.Therefore,the ultrasonic phased array testing technology for internal defects in large stainless steel castings is proposed.The necessity of partitioned testing for thick castings and the optimal selection of ultrasonic phased array transducers for each partition are analyzed,and then the use of the-6dB method for quantitative defect detection is proposed.The results show that the ultrasonic phased array testing technology can effectively detect internal defects in large stainless steel cast-ings,in which the detection sensitivity is not less than φ3mm flat-bottom hole equivalent size within a thickness of 60mm.The relative errors of the-6dB method in measuring the sizes of far and near surface defects are respective less than 26.7％and 16.7％,indicating its suitability for quantitative non-destructive testing of large thickness stainless steel castings.
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