Phased array inspection of narrow-gap weld LOSWF defects for in-process weld inspection

Post-manufacturing weld inspection processes within the oil, gas and nuclear industries are crucial in ensuring the integrity of critical components. Non-Destructive Evaluation (NDE) utilising Ultrasonic Phased Array Testing (PAUT) techniques are currently preferred to perform post-welding inspections, enabling correction of potential flaws before components are used in the field.
However, this process can be refined to increase manufacturing efficiency and reduce production costs while maintaining quality assurance. The marriage of the welding and inspection processes, widely termed ‘In-Process Inspection’, allows potential flaws to be detected, analysed, and corrected if necessary, between individual weld passes. Not only does this increase throughput by combining two separate processes, but also reduces the rework and disruption experienced by current practices. The feasibility of the in-process technique has been successfully shown using high-temperature ultrasonic wheel probes for standard V-groove welds. Despite this, the technique has not yet been applied to other welding practices, such as narrow-gap.
Narrow-gap welds are typically chosen to reduce required weld volume and heat input to manufacture thick-section components, such as pressure vessels, modular reactors and gas storage tanks. Notoriously difficult to consistently inspect, narrow-gap weld inspection methods would greatly benefit from an in-process technique. This would allow flaws in initial passes to be detected early, and reduce the requirement to excavate large volumes of deposited weld material to correct.
Despite the obvious advantages, an in-process method introduces added challenges for ultrasonic inspection, particularly due to effects observed from added geometric reflections from partial weld geometries, industrial process interference, and high temperature gradients. Furthermore, an inspection plan which optimises probe position to maximises acoustic energy for inspection of each pass as it is deposited would be crucial.
A dual-tandem inspection method has been proposed to ensure consistent detection of simulated Lack-of-Sidewall Fusion (LOSWF) defects in mock narrow-gap weld samples. This includes two opposite-facing phased array probes on each side of the weld, to ensure uniform coverage from each weld side, and to improve system sensitivity to diffractive effects. Near-vertical 5.0 mm x 1.0 mm EDM notches in 120.0 mm thick Carbon Steel mock weld samples have been detected and sized using a dual-aperture Full Matrix Capture (FMC) data acquisition and Multi-Mode Total Focussing Method (MMTFM) algorithm.
Using a path-finding Time-of-Flight (ToF) calculation algorithm, this method has also been shown to successfully adapt to partial weld inspection through geometric compensation, with detection and sizing of EDM notches in mock partial narrow gap samples. Through data fusion techniques, vertical notch detection and characterisation is greatly enhanced relative to traditional phased array methods.