Abstract: A series of physical and chemical tests including macroscopy examination, scanning electron microscopy, chemical compositions analysis, microstructure testing, and mechanical properties testing were applied to analyse the failure causes of naphtha socket welding pipeline. The results indicate that the socket welding pipeline fracture belongs to brittle fracture. The unsuitable welding technology leading to internal micro-cracks near welding fusion line, coarse grain in heat-affected zone and high residual stress is the main cause of brittle fracture for the naphtha socket weld pipeline. Finally, recommendations to prevent similar incidents were put forward.