Phased Array (Phased Array UT)

Phased Array Ultrasonic Testing (PAUT) is an advanced ultrasonic inspection method that uses a probe made up of many small piezoelectric elements (typically 16, 32, 64 or 128 elements) instead of a single crystal. Because each element can be excited individually with delay laws (focal laws) in the microsecond range, the resulting sound wave front can be steered to any desired angle in software, focused at a specific depth and swept through the material without physically moving the probe. Controlled shifting of the element firing sequence provides beam steering and focusing, which makes it possible to capture discontinuities of different orientations within a single scan compared with conventional single-element UT.

The fundamental advantage of the method is that the acquired data can be presented in image form. In conventional UT the operator interprets only the A-scan signal, whereas in PAUT these signals are converted into two-dimensional cross-sectional images such as the S-scan (sectorial/angular scan), the E-scan (electronic linear scan) and the C-scan. An S-scan sweeps a range of angles — for example between 40° and 70° — from a single probe position and produces a sectorial map of the weld cross-section; this allows discontinuities oriented at different angles (lack of side-wall fusion, root defects, slag) to be evaluated in the same image. Because the position, depth and size of discontinuities can be read directly from the image, the inspection is understood in a three-dimensional way and the results are stored as archivable records.

In practice a PAUT system comprises a multi-channel instrument, a phased array probe, a wedge that sets the coupling angle of the probe to the material, and usually an encoder. The encoder records the probe position along the scan line and links every data line to a real position, so that flaw length and location are documented correctly along the weld. Focal laws are calculated and verified on calibration blocks according to the thickness and geometry of the part to be inspected and the probe-wedge combination. In sweep mode a wide angular range is covered from a single probe position, which increases inspection speed and optimises the scanning coverage in areas with restricted access.

In weld inspection PAUT is increasingly used as an alternative or complement to radiography; particularly in pipe and pressure vessel welds of greater wall thickness it provides high sensitivity for planar defects such as lack of side-wall fusion, where the fusion direction is critical. When applied together with Time-of-Flight Diffraction (ToFD), the strength of PAUT in detecting near-surface and planar flaws combines with the accuracy of ToFD in flaw height sizing to form a radiography-free inspection strategy (encoded PAUT + ToFD). The method is also used for corrosion mapping, evaluation of cladding/liner disbonding and assessment of volumetric flaws in cast and forged components.

Evaluation and reporting are based on the acceptance criteria defined by the applicable execution standard. Flaw sizing is generally performed on an amplitude basis against reference calibration reflectors (side-drilled holes, notches) or by the diffraction/tip-echo technique using flaw tip signals; the recorded S/C/E-scan images form an integral part of the report and ensure that the inspection remains traceable and repeatable. This traceability and imaged documentation is the main reason PAUT is preferred across a wide range of applications, from manufacturing quality control to periodic inspection and life extension studies. TÜV AUSTRIA SILA KALİTE performs Phased Array inspection with qualified and certified personnel, within the scope of its TS EN ISO/IEC 17020 accreditation and in accordance with the relevant national and international standards.