Phased array ultrasonic evaluation of domestic and imported thermite welds: defect detection and performance analysis in railroad applications

This study demonstrates the superior capability of Phased Array Ultrasonic Testing (PAUT) over conventional ultrasonic methods for inspecting thermite welds in railroad applications. The research evaluated both domestically produced and imported thermite powders (two Asian and two European brands), with PAUT proving significantly more effective in detecting and characterising critical defects. The system successfully identified distributed microporosity (2–53 μm) and centre-line imperfections at weld interfaces, while conventional methods showed limited detection sensitivity for sub-surface flaws. PAUT enabled precise quantitative analysis, establishing a strong correlation between material hardness and signal quality (SNR = 0.15·HV − 30.5, R2 = 0.89) and detecting porosity clusters exceeding 50 μm known to reduce fatigue life by 40–60%. The domestic thermite powder demonstrated equivalent performance to imported alternatives in chemical composition, mechanical properties, and microstructural characteristics. PAUT’s multi-angle scanning capabilities and superior signal processing provided enhanced detection reliability in coarse-grained thermite microstructures, particularly for internal flaws that conventional methods frequently missed. This research validates both the cost-effectiveness of domestic thermite materials and PAUT’s critical role in modern rail maintenance, especially in challenging environments like Southeast Asia’s tropical climate, where rail integrity is paramount for transportation safety.