Tham khảo tài liệu 'volume 17 - nondestructive evaluation and quality control part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3 This example demonstrates techniques applied to mm C in. outside diameter stainless steel tubing with a mm in. wall thickness. However these techniques can be modified to enable detection of intergranular attack and or root weld cracking in various materials and sizes. _3_ 3 A 15-MHz Rayleigh surface wave transducer is machined with a mm I I in. radius to fit the mm C in. outside diameter of the mm in. wall thickness tubing to be inspected Fig. 13a . The transducer is then positioned on the tubing as shown in Fig. 13 b . No prior preparation of the sample was required. Mixed-mode shear wave is induced in the tubing to detect intergranular attack Fig. 14 using a ring-pattern CRT display Fig. 15 . This transducer is also very sensitive and can be used for detecting root weld cracks Fig. 16 . The ultrasound instrument will be set up for monitoring discrete echoes from the root crack. The display produced is shown in Fig. 17. Fig. 13 15-MHz Rayleigh surface wave transducer 90 shear used for detecting intergranular attack and root weld cracks. a Transducer with radius machined on transducer shoe to allow device to conform to tubing outside diameter. b Transducer positioned on tube outside diameter to couple to tube using a lightweight oil couplant. Source . Cox General Dynamics Corporation Iri M Fig. 14 Intergranular attack of mm in. wall thickness Fe-21Cr-6Ni-9Mn stainless steel tubing inside diameter. a 60X. b 85x. Courtesy of . Cox General Dynamics Corporation Fig. 15 Mixed-mode shear wave used to detect intergranular attack showing oscilloscope screen display for a transducer in air b transducer coupled to an acceptable tube having no defects due to intergranular attack and c transducer coupled to tube rejected because of intergranular attack. Significant attenuation of the ultrasonic signal in c is due to scatter. Source . Cox General Dynamics Corporation Fig. 16 Cross section of a tube having a crack at the .
