The mechanical processing department of a petrochemical unit, when manufacturing pressure溶弹外壳 and miniature reactor joints, etc., requires ultrasonic non-destructive testing of semi-finished stainless steel bars. Past non-destructive inspection methods involved cutting the stainless steel bars supplied by the vendor into suitable short segments, rough turning the outer diameter, and making flat ends; after visual inspection, straight probe contact method was used for testing from the two end planes of the cylinder, and cylindrical surfaces were tested using straight probe circumferential and longitudinal water immersion methods. This approach resolved the issue of water immersion tank length limitations for the tested material length. However, this testing method became destructive for the inspection. Once defects were detected, it was difficult to return or exchange, resulting in material waste, increased processing costs, and losses for the unit. On the other hand, the results from this method indicated that defects were rarely found when testing with the straight probe contact method from the two end surfaces of the cylinder; however, semi-finished products that passed the inspection still occasionally exhibited longitudinal cracking during pressure testing and usage.