Unusual ultrasound :: PA + SAFT

The customer has set a task to provide the AUT of the fusion line of two parts made from austenitic steel. The thickness of the part was about 150 mm. The obligatory conditions were:

• application of the phased array flaw detector already owned by the customer, the device had only 16 active channels for focusing.

• detection of a 1 mm FBH and measurement pf defects dimensions with high accuracy (~ 1 mm)

The task could be solved with the help of straight-beam probe, providing XY-scanning and SAFT-type coherent processing. For example of such approach see the paper.

However, in order to satisfy the customer’s requirements for the use of a phased arrays flaw detector, the following tricks were required:

— create the focal laws, simulating 15 transducers with different angles of incidence of the longitudinal wave;

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— the data acquired while scanning with a 0,4 mm step and processed to the coherent SAFT-type method;

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— process all the data coherently and obtain an image with high resolution (on the image below — simple PA image for one position and PA+SAFT processed image);

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— it was necessary to create a special algorithm for calibrating the parameters of the phased array operating in such an unusual mode, the calibration was performed at the SDH

The required sensitivity and measurement error was achieved.

There was one problem — the image of the FBH looked not round, but oval because of the lack of focusing in the plane perpendicular to the incidence plane. With the use of a straight beam probe with a round plate, this problem would not arise. In this case, the procedure had to include an additional scanning with phased array rotated by 90 °.

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