Pulse echo immersion

In service inspections of French nuclear Pressure Water Reactor (PWR) vessels are carried out automatically in complete immersion from the inside by means of ultrasonic focused probes working in the pulse echo mode. Concern has been expressed about the capabilities of performing non destructive evaluation of the Outer Surface Defects (OSD), i.e. defects located in the vicinity of the outer surface of the inspected components. OSD are insonified by both a "direct" field that passes through the inner surface (water/steel) of the component containing the defect and a "secondary" field reflected from the outer surface. Consequently, the Bscan images, containing the signatures of such defects, are complicated and their interpretation is a difficult task. 

Figure U.l Ultrasonic inspection techniques, (a) Contact pulse echo with a search unit combining a transmitter and receivers, (b) Contact through transmission. Transmitting search unit on top and receiving search unit on the bottom, (c) Immersion pulse echo with search unit (transmitter and receiver) and part inspected under water, (d) Immersion through transmission with both search units (transmitter and receiver) and part under water, (e) Immersion reflector plate. Same as (c) but each unit requires a reflector plate below the part being inspected. (Ref Hagemaier, D.J., End Product Nondestructive Evaluation of Adhesive Bonded Metal Joints , Adhesives and Sealants, vol. 3, Engineered Materials Handbook, ASM International, Materials Park, OH, 1990)...

Nondestructive testing. An ultrasonic inspection technique is available for the detection of flaws in plate, piping, and tubing. The water-immersed pulse-echo ultrasound equipment has been adapted to highspeed use. Eddy-current, dye-penetrant, and radiogr.aphic inspection methods are also used as required. The inspected materials have included Inconel, austenitic stainless steel, INOR-8, and the Hastelloy and other nickel-molybdenum-ba.se alloys. 

For immersion probes we also get similar improvements using piezocomposite transducers as demonstrated by the third example. In Fig. 8 we compare pulse form and frequency spectrum for a 2 MHz probe Z2K with 10 mm transducer diameter. The echo of the composite probe has 11 dB more amplitude and is clearly shorter than for the old design, also indicated by the increase in bandwidth from 45 to 76 %. 

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