ASNT Level II in PAUT

About ASNT Level II in PAUT

The Phased Array Technique is a process wherein UT data are generated by controlled incremental variation of the ultrasonic beam angle in the azimuthal or lateral direction while scanning the object under examination. This process offers an advantage over processes using conventional search units with fixed beam angles because it acquires considerably more information about the reflecting object by using more aspect angles in direct impingement. Each phased array search unit consists of a series of individually wired transducer elements on a wedge that a reactivated separately using a pre selectable time delay pattern. With a linear delay time between the transmitter pulses, an inclined sound field is generated. Varying the angle of refraction requires a variation of the linear distribution of the delay time. Depending on the search unit design, it is possible to electronically vary either the angle of incidence or the lateral skew angle. In the receiving mode, acoustic energy is received by the elements and the signals undergo a summation process utilizing the same time delay pattern as was used during transmission.

Flaw sizing is normally performed by measuring the vertical extent (in the case of cracks) or the cross sectional distance (in the case of volumetric/planar flaws) at the 6 dB levels once the flaw has been isolated and the image normalized. Tandem sizing and analysis uses techniques similar to pulse-echo but provides images that are easier to interpret since specular reflection is used for defects oriented perpendicular to the surface. For cracks and planar defects, the result should be verified using crack tip diffraction signals from the upper and lower ends of the flaw, since the phased array approach with tomographic reconstruction is most sensitive to flaw tip indications and is able to give a clear reconstruction image of these refraction phenomena. As with other techniques, the phased array process assumes isotropic and homogeneous material whose acoustic velocity is constant and accurately known.

Sectorial scans (S scans) with phased array provides a fan like series of beam angles from a single emission point that can cover part or all of a weld, depending on search unit size, joint geometry, and section thickness. Such a series of beam angles can demonstrate good detectability of side drilled holes because they are omni directional reflectors. This is not necessarily the case for planar reflectors (e.g., lack of fusion and cracks) when utilizing line scanning techniques where the beam could be misoriented to the point they cannot be detected. This is particularly true for thicker sections when using single line scanning techniques.

ITE has expert manpower with years of expertise in performing PAUT of various components including Welding, Castings, Pipes, Tubes, Plates, etc.

As a recent addition to the portfolio of our services we have started performing Phased Arrau Ultrasonic Testing of Boiler Tubes as well with diameter as low as .75 inch to 4.5 inches. This is done used a specialized attachment called Cobra scanner. Cobra scanners used with  Olympus Omnis can MX2 with other necessary accessories to perform reliable scanning of Boiler Tubes welded joints. With Cobra Scanner, we have been able to remove various challenges and limitations faced by customers in the power sector. One of them being reduced dependence of Radiography Testing, since PAUT using cobra scanner give better and faster result that Radiography Testing.

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