Effect of G-Phase Precipitation on Creep-Damaged SS 347H Platen Superheater Boiler Tube Failure

The failure of a platen superheater tube of SA213-TP347H grade austenitic stainless steel was investigated through chemical, metallurgical, mechanical, and microstructural analysis and scanning electron microscopy. A marginal reduction in hardness of the serviced tube with depletion of chromium in the matrix compared to the virgin tube material was observed. While the yield and tensile strengths remained within limits, the elongation property was decreased significantly, indicating the occurrence of localized embrittlement. The effect of the complex silicide phase in the matrix in conjunction with Cr23C6 precipitates along the grain boundaries on the embrittlement of tube material has been studied. These findings emphasize the role of microstructural stability in premature tube failures under high-temperature environments.