Pressure Vessels Inspections Using Ultrasonic Phased Arrays

Abstract

Phased arrays offer significant technical advantages for weld inspections over conventional ultrasonics. The phased array beams can be steered, scanned, swept and focused electronically. Beam steering permits the selected beam angles to be optimized ultrasonically by orienting them perpendicular to the predicted defects, especially Lack of Fusion. Electronic (linear) scanning permits very rapid coverage of the welds. Beam steering (usually called sectorial or azimuthal scanning) can be used for mapping welds at appropriate angles to optimize Probability of Detection of defects. Electronic focusing permits optimizing the beam shape and size at the expected defect location, also to optimize Probability of Detection. Overall, the use of phased arrays permits optimizing defect detection while minimizing inspection time. The paper describes the application of phased arrays for inspecting pressure vessel welds. Phased arrays offer significant practical advantages over conventional automated inspections. Thick section weld inspections typically use the established “top, side, end” or “top, side, TOFD” views of the weld. Other displays can be used, e.g. strip charts for zone discrimination scanning of narrow gap welds. Special inspections can be easily performed with phased arrays, e.g. additional beams for extra coverage, multiple angles or inspection set-ups simultaneously, or special scans such as tandem probes. Different delivery systems and instrumentation can be assembled for any required scan. Fitness-For-Service inspections requiring high PoD and accurate sizing can be performed using upscale systems. These phased array inspections can be tailored to any known code requirements.