Multi-mode plane wave imaging based full-section inspection for ultra-thick welds with the compact array

Full-section ultrasonic non-destructive testing of ultra-thick welds (thickness >90 mm) traditionally requires multiple transducer groups with multiple scanning to achieve full coverage, resulting in bulky equipment and low inspection efficiency. This study presents a multi-mode plane wave imaging (MM-PWI) technique that enables efficient, full-section inspection of ultra-thick welds using a single compact transducer array. The proposed method decouples various skipping modes of longitudinal and shear waves to reconstruct flaws throughout the weld from top to bottom. To address signal attenuation caused by multiple wave skips, the vector coherence factor (VCF) is applied, significantly improving the signal-to-noise ratio (SNR) of the images. Experimental results demonstrate that a 120-mm-thick weld can undergo fully inspection using a 64-element array with a 0.6 mm pitch. All flaws can be inspected in a single scan with SNRs exceeding 32 dB. The main advantage of the proposed method lies in its simplicity and stability in the testing process, which can significantly improve inspection efficiency and be easily applied in industrial inspections.