<\/div>\n
The UT principle<\/h2>
The principle rests on the propagation of high-frequency elastic waves (ultrasound) through the material. A piezoelectric transducer (usually PZT) generates very short ultrasonic pulses (tenths of a \u00b5s) that enter the material through a couplant (gel, water or oil, to ensure acoustic transmission between probe and workpiece). The waves travel at a known velocity (for example 5920 m\/s for longitudinal waves in steel) and are reflected at every internal discontinuity (cracks, inclusions) or at the opposite surface. The same transducer (in pulse-echo mode) or a second transducer (pitch-catch mode) detects the reflections, and the electronics analyze the signals in the time domain (A-scan). <\/p>
Types of flaw detector<\/h2>
Modern flaw detectors are compact portable instruments with a real-time A-scan, gates for automatic detection of defect echoes, calibration of vertical (amplitude) and horizontal (time\/distance) linearity, DAC (Distance Amplitude Correction) functions for evaluating defects at different distances from the probe, TVG (Time Varied Gain) to compensate for material attenuation, and AVG\/DGS functions for defect sizing. The most advanced models incorporate Phased Array UT (with multi-element transducers and electronic beam steering), TOFD (Time-Of-Flight Diffraction), and B-scan and C-scan for defect mapping. <\/p>
Transducers and probes<\/h2>
UT transducers differ in: frequency (0.5-1 MHz for thick, attenuating parts such as cast iron; 2-5 MHz for standard applications on steel; 10-15 MHz for high-precision measurements on thin materials); geometry (direct contact – single crystal, dual element, twin-line; angle beam – 45\u00b0, 60\u00b0, 70\u00b0 for weld inspection; immersion); size (from a few mm to tens of mm in diameter); and coupling method (contact with couplant; water immersion; air-coupled for special applications). The choice of transducer follows from the material, the thickness, the type of defect expected and the inspection technique. <\/p>
Applications<\/h2>
The industrial applications are varied: weld inspection (checking for cracks, lack of fusion, slag inclusions and porosity – to sector standards such as EN 17640 for UT on welds); acceptance of forgings and castings (dealing with central porosity and segregation); in-service inspection of piping, pressure vessels and tanks (to find fatigue cracks and localized corrosion); inspection of railway wheels and axles to prevent catastrophic failures; aeronautical inspections (testing structural components in light alloy); and R&D in the materials sector.<\/p>
Reference standards<\/h2>
The main standards are: ISO 9712 (NDT personnel qualification, levels 1-2-3); ISO 17640 (UT of welds); ASTM E164 (contact UT); EN 12668 (characterization of UT equipment); EN 583 (parts 1-6, UT test procedure). Specific personnel qualifications for aerospace applications follow NAS 410. UT instruments are calibrated with V1 reference blocks (for linearity and basic calibration) and V2 blocks (for small-angle applications). Transducers are verified with dedicated blocks for amplitude, frequency and pulse width. <\/p>
Selection criteria<\/h2>
The choice of flaw detector depends on: the application (plain UT versus Phased Array versus TOFD); the range of thicknesses and materials to be inspected; portability (compact units for on-site service, benchtop units for the laboratory); an A-scan display alone or also B\/C-scan and 3D imaging; compliance with sector standards (for aerospace, power generation, nuclear); software for analysis and for generating ASNT\/EN 17637 reports; and the supplier’s support and instrument qualification service.<\/p>","protected":false},"excerpt":{"rendered":"
UT instruments for locating cracks, lack of fusion and internal defects in welds and materials.<\/p>\n","protected":false},"author":157040980,"featured_media":0,"parent":19505,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_yoast_wpseo_focuskw":"","_yoast_wpseo_title":"","_yoast_wpseo_metadesc":"","_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","_wpcom_ai_launchpad_about_page":false,"_wpcom_ai_launchpad_gallery_page":false,"_wpcom_ai_launchpad_contact_page":false,"_wpcom_ai_launchpad_events_page":false,"_wpcom_ai_launchpad_video_page":false,"_wpcom_ai_launchpad_portfolio_piece":false,"footnotes":""},"class_list":["post-22348","page","type-page","status-publish","hentry"],"yoast_head":"\n
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