PixTransNet: A Sensor-Aware CNN–Transformer Model for Magnetic Flux Leakage Defect Segmentation

Abstract

Magnetic flux leakage (MFL) is a widely used nondestructive evaluation technique for pipeline inspection. However, its signals are highly sensitive to noise and geometric distortions, causing small defects with limited spatial coverage and subtle defects with low-contrast patterns to be embedded in noise, resulting in indistinct boundaries and irregular shapes that complicate segmentation. To address these challenges, we propose PixTransNet, a hybrid convolutional neural network (CNN)–Transformer model built on a UNet encoder–decoder architecture with a ResNet18 backbone, designed to improve the segmentation and boundary localization of small and subtle defects in MFL signals. We embed pixel-aware transformer blocks into the deeper encoder stages to capture long-range dependencies and enhance the modeling of subtle and fragmented defect patterns. To further enhance the interpretation of MFL signals, we introduce a cross-attention module that selectively emphasizes signal regions with strong structural relevance, leading to more continuous and accurate defect boundaries, particularly for small defects. Extensive experiments on a large-scale dataset of 33 000 MFL images demonstrate that PixTransNet achieves notable improvements in segmentation quality, particularly in detecting small, weak, and low-contrast defects compared to existing baselines. PixTransNet achieves 48.30% intersection over union, representing a 1.97% improvement, and 70.73% recall, representing a 13.06% improvement over the best-performing baseline.