STUDY ON ULTRASONIC PHASED ARRAY IMAGING TECHNIQUE FOR DIRECT CONTACT INSPECTION ON DOUBLE CURVED SURFACE

Ultrasonic testing technique is commonly used for non-destructive inspection of pressure vessels and pipelines. Normally, ultrasonic phased array system can effectively and efficiently image different types of defects within the structures through direct contact method. However, the double curved geometries of inspection targets (e.g. pipe elbows, pipe weld joints and turbine blades) give rise to challenges in direct contact between probe and surface. Therefore, based on the full matrix capture and total focusing method (TFM), this paper uses a conventional phased array transducer with flexible wedge to detect and image a double curved sample with different depths of side drilled holes. The test specimen is fabricated in a ring shape with an outer diameter of 150 mm, an inner diameter of 100 mm and a 2 mm high weld reinforcement. It is found that the full matrix data can be captured to image the structure interior by either extracting the surface profile or directly imaging with preset surface dimensions. The proposed technique has also demonstrated its capability on realizing high-resolution imaging of 1 mm side drilled holes at different depths. Our promising results show that the method has the ability to reliably locate and quantitatively evaluate the defects with complexly shaped structure.