Failure Analysis of TP304 Stainless Steel Tee

Cracks formed in a TP304 stainless steel tee in the denitration facilities of a power plant. The failure cause of the tee was studied by means of composition analysis, macroscopic and microscopic analysis, microstructure observation and hardness measurement, as well as production process analysis. The results show that the Ni content of material is lower than the standard requirement, which reduced the stabilization degree of austenite. Spherical non-metallic inclusions with the scale of 2.5~3.0 in the substrate had tearing effect on matrix and promoted the initiation of fatigue crack. There is also no solid solution treatment in the production, resulting in excessive internal stress. The factors above led to the lower content of austenite, higher hardness, and higher local stress concentration. In addition, there are lots of processing damages on the inner surface of tee, aggravating the stress concentration phenomenon. Ultimately, under the action of fatigue load, the crack initiated.