Ultrasonic testing involves use of high frequency sound waves coupled to the components to be inspected and studying the reflection pattern of these waves. UT is finding many more applications in numerous industries. Several wave modes such as longitudinal, shear and surface waves can be used con-finding on the orientation and location of the discontinuities. Diverse techniques such as pulse-echo, through transmission, along with pitch-catch or engaged. The advantages of UT are real time possibility of results, higher penetrating power of these waves, greater sensitivity for planner defects, individual sensitivity over depths, economical for inspection, higher portability to the equipment and compatibility for automation. But the individuality of the results on the operators training and skill is stumbling block for its wider recognition. With the advent of microprocessors and automation, operator dependability is being Phased out to a larger extent and UT finding increased applications in industries such as power, railways, chemical, aerospace and so on.
UT of cast metals and alloys is rendered difficult due to the influence of casting complexity, micro structural variations and surface roughness. Defects existing in the cast structure have irregular surfaces which scatter the aquatics waves and makes UT more challenging. Hence successful use of UT for inspection of castings depends greatly upon the skill and expertise of the operator.
UT is the most suitable method of NDT for in-service inspection (ISI) of components in power plants, chemical process industries, and the rest. Often, RT cannot be applied for ISI due to the requirements of two side accessibility. UT is much more sensitive flaw growth monitoring has compared with RT in view of all these advantages , the first choice of ISI is UT for volumetric defects in components except for heat exchangers and condensers where ECT is preferred.