Phased array ultrasonic testing technology and its development

Phased array ultrasonic testing technology is an advanced ultrasonic testing technology that emerged in the 1990s. This technology achieves ultrasonic beam movement, deflection, and focusing functions through applying different time delay rules (focusing rules) to different units in the transducer array during the emission or reception of sound waves. The principles of beam movement, deflection, and focusing are shown in Figure 1, and the ultrasonic imaging display is shown in Figure 2.

A phased array ultrasonic testing system mainly consists of a transducer array and a control unit. The transducer elements are arranged according to certain rules and have independent sending/receiving control modules. When the transducer is in the transmitting state, the control unit controls the transmission delay time of each transducer element according to a certain delay rule, thereby controlling the focusing and direction of the emitted ultrasonic beam, and achieving the movement, deflection, and focusing of the beam within a certain range. The transducer receiving process also follows the above geometrical focusing delay rules, and is the inverse process of the transducer transmitting state. During detection, the sound beam propagates in the medium according to a certain rule. When the acoustic impedance changes at the defect in the medium, a reflection signal with a certain sound intensity will be generated. The path of this point to each element of the transducer array is different, resulting in a certain difference in the time it takes for the reflection signal generated at this point to reach each element. Each element performs time-delayed summation on the echo signal according to the set delay Δt, so that the echo signals from the defect are in phase, achieving the purpose of enhancement and realizing receiving focus. The principle of phased array ultrasonic testing is shown in Figure 3.

Figure 3 Phased array detection principle diagram

The earliest application of phased array ultrasonic technology began in the field of medical ultrasonic diagnosis in the 1970s; in the early 1980s, phased array ultrasound developed from the medical field to the industrial field; in the mid-1980s, with the rapid development of computer technology, phased array ultrasonic imaging technology was gradually applied to important industrial fields such as aerospace and nuclear industry; in the 1990s, with the successful development of small and portable phased array ultrasonic devices, phased array ultrasonic technology has rapidly developed and been widely applied in various fields.

Abroad, phased array ultrasonic testing technology has been widely used in aerospace, petrochemical, power, and nuclear industries, such as aerospace special weld detection, aircraft fuselage corrosion C-scan detection, chemical hydrocracker special weld and position detection, large turbine blade root crack detection, nuclear vessel thick plate dissimilar metal weld detection, long-distance oil and gas pipeline butt weld detection, etc.; In China, with the introduction of phased array ultrasonic technology in the late 1990s, significant progress has been made in the development of phased array ultrasonic equipment and technological applications in recent years. Currently, there are many application cases in aerospace, nuclear industry, bridges, and national defense. In the aerospace field, literature records the use of phased array ultrasonic dynamic focusing methods to achieve good detection results and high detection efficiency for micro-defects (Ф0.4-14dB) in aero-engine powder high-temperature alloy disc parts. Using water-jet coupled phased array C-scan technology, delamination defects in aircraft composite materials can be quickly detected while meeting the detection requirements; in the nuclear industry, using phased array ultrasonic testing for ultra-thick plate dissimilar metal butt welds achieves detection results that conventional ultrasound cannot achieve; in bridge manufacturing, phased array ultrasonic technology has been successfully used to measure the penetration depth of the U-rib fillet welds of large bridge steel box girders; in the field of national defense, phased array ultrasonic technology is used to inspect the welding quality of special position welds in deep-sea submersibles, achieving very ideal results.

In line with the development and application of phased array ultrasonic technology, phased array ultrasonic testing standards have also been promulgated and implemented at home and abroad, covering many aspects such as instruments, probes, test blocks, and testing methods. The main standards are shown in Table 1. The American ASME standard, Section V, Appendix IV and V, specifically details manual phased array ultrasonic testing of welds and the use of E-scan and S-scan to inspect welds; standards such as ASTM E2491 and E2700 detail the principles, processes, and performance evaluation of phased array technology and provide relevant application examples; GB/T32563 is the first domestic standard for phased array ultrasonic testing methods, which describes the phased array ultrasonic testing methods and process design in detail.

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