Quantitative non-destructive evaluation analysis and characterisation of microcrack detection based on carbon steel weld under alternating current field measurement

Nondestructive testing of microcrack in welding seams is a key and challenging task in nuclear industry to evaluate material properties. The real magnetic characteristics of welds and stress redistribution have not been considered in the previous numerical simulation of welds and base metal materials, which leads to conservative calculation values and fails to meet actual engineering expectations. In this work, based on the difference between weld and base material structure, a non-uniform weld magnetic charge model was established and the stress distribution characteristics of weld cracks were analysed. The characteristics and gradient distribution of magnetic signals at weld and weld crack are calculated. The work quantitatively studied and characterised the influence of the offset weld position of the detection probe, the distance between the crack and the probe, the crack cluster, and the crack at the interface between the weld and the base metal on the detection signal. The microcrack detection of base metal, weld, and interface under various working conditions was compared and analysed. The difficulty of the AC electromagnetic method in weld inspection is solved, and the weld microcrack identification is realised. The results provide theoretical guidance for the identification of potential weld microcracks in spent fuel pools.