Variations of the microstructure and mechanical properties of HP40Nb hydrogen reformer tube with time at elevated temperature

Hydrogen reformer furnaces have been widely used in the petrochemical industry to produce the hydrogen-rich gas from a mixture of hydrocarbons and steam at high temperature. However, the degradation of material microstructure was frequently encountered in the tubes due to high temperature service, leading to their premature failure. The aim of this paper was to address the variations of the microstructure and mechanical properties of HP40Nb hydrogen reformer tubes after aging treatment and long-term service at temperature of 900 °C. The results showed that the grain boundaries became coarsening due to the precipitation of the chromium-rich carbides and the secondary carbides precipitated in the matrix after aging treatment and long-term service. The mechanical properties of the HP40Nb tube obviously degraded after short-term service and then almost kept unchanged. The interdendritic carbide content can be used as a key index for the life predication of the used tube since there was a linear relationship between the logarithm of carbide content and the logarithm of time.