Welding Practice - The Hong Kong Polytechnic University

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Welding Practice 4.2.2 Ultrasonic testing Ultrasonic testing utilizes mechanical vibration in detecting imperfections in materials. At very high frequencies such as 1 to 10 megacycles, mechanical vibration can be generated in the form of well defined beams of small cross section. These beams can be directed into work pieces on internal examination somewhat in the manner of X rays. Like other wave motions, the beams are subject to the laws of reflection and refraction when they encounter changes in the physical properties governing the propagation of vibrational waves. Thus any unhomogeneity can be detected as this represents a substantial change in either the elastic modulus or the density of the material. In practice, commercial instruments do not measure these parameters directly; instead they indicate one or more-of the factors involved in sound-wave propagation; velocity of travel, attenuation of beam, and reflection of energy from discontinuities. 4.2.3 Radiographic Radiographic method of inspection utilizes the shadow pattern resulting from penetrating radiation to determine a material's homogeneity. This inspection process requires a source of penetrating radiation such as radioisotopes or X-ray generators, and recording devices such as film or fluoroscopic screens. Inspection is accomplished by registration of discontinuities in the material on the observing medium, and relating them to the material's physical properties. Page 10 IC Professional Training
Welding Practice References The Procedure Handbook of Arc Welding, The Lincoln Electric Company. ASM Handbook Volume 6, 6A American Welding Society Last Updated: Jun 2012 Page 11 IC Professional Training
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Welding Practice - The Hong Kong Polytechnic University

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