Recently deposited weld layer-targeted parametric optimization for ultrasonic in-process inspection of narrow gap welds

ABSTRACT Escalating cost and schedule pressures are accelerating the shift from end-of-line non-destructive testing (NDT) to in-process ultrasonic inspection during the manufacture of safety-critical components. In the nuclear sector, thick-section pressure vessel components fabricated from SA508 steel (high-strength, low-alloy ferritic steel) are commonly joined using narrow-gap (NG) submerged arc welding (SAW) to reduce weld volume. In-process inspection of NG welds is challenging because travel speeds (∼10 mm/s) demand frame rates ≥10 frames per second (FPS), while near-vertical fusion faces, evolving groove geometry, thermal-gradients and coupling degradation deteriorate image quality. This work presents a novel parametric optimization strategy based on the recently deposited weld layer for a multi-layer ultrasonic inspection based on tandem plane-wave imaging (PWI). Probe centre separation (PCS) and PW sweep angle calculations are defined to direct acoustic energy to the current deposited layer, while satisfying in-process acquisition-rate constraints. The approach is validated on 120 mm thick partially filled NG calibration blocks, containing Electrical-Discharge-Machined (EDM) notches (5 mm × 1 mm), mimicking lack-of-sidewall-fusion (LOSWF) indications. An Eikonal travel-time solver was used to model PW propagation through the evolving NG geometry. Sign Coherence Factor (SCF) weighting enhanced defect sensitivity across all modes by suppressing incoherent noise due to attenuation and evolving weld geometry-based scattering. Compared with tandem Full Matrix Capture method (FMC-SCF) baselines using PCS definitions based on fractions of cumulative weld-fill-height, the proposed tandem PWI-SCF strategy achieves around 9.39 dB higher mean Signal-to-Noise Ratio (SNR) in direct-hit mode while providing acquisition rates compatible with in-process SAW, enabling layer-specific weld monitoring.