Ultrasonic Examination (UT)
UT is a very versatile NDE method. A variety of techniques have been developed for using UT to detect most forms of deterioration that can occur during service. Both surface and internal flaws in a vessel shell can be detected from either the O.D. or I.D. surface, and internal corrosion loss can be determined without access to the inside of the vessel.
Of all NDE methods UT is the most able to determine flaw size with sufficient accuracy to evaluate the integrity and reliability of a vessel, and to make fitness-forservice analyses. However, the accuracy of the sizing data obtained is highly dependent on the procedure used, and the qualifications and experience of the technician performing the examination.
Article 5 of ASME Code, Section V, gives the minimum requirements for a UT procedure for the in-service examination of a pressure vessel. However, these minimum requirements may not be adequate for the reliable detection and accurate sizing of some types of flaws that can occur during service. Specialized UT techniques are discussed below that can greatly improve detection and sizing capabilities.
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