Abstract: A SA213-TP347H steel superheater tube of a subcritical boiler burst. Metallographic observation, hardness testing, SEM observation and energy spectrum analysis were conducted to find out the failure cause. The results show that the grain size of the austenite coarsened apparently, and Cr₂₃C₆ precipitates in the grain boundaries led to chromium depletion in the grain boundaries. As a result, the corrosion resistance degraded. Finally, the tube burst because of intergranular corrosion under the long-time high temperature or sometimes even overheating. The present work is of great significance to figuring out the service situation of the material. Some suggestions were put forward to prevent such accidents.