Annealing of Shot Peened Austenitic Superheater Tubes and Its Consequences for Steamside Oxidation

Surface modifications offer promising solutions to increase the lifetime and performance of superheaters in industrial applications. The surface and internal structure of the steamside of austenitic superheater tubes of TP347H austenitic stainless steel was modified by shot peening and the thermal stability of the microstructure at the surface was followed in-situ and ex-situ during subsequent isothermal annealing.

At various industrially relevant temperatures, the kinetics of microstructure evolution near the surface was investigated by applying complementary methods of microscopy and diffraction analysis. The beneficial effect of shot peening on reducing steamside oxidation was confirmed both on laboratory scale mimicking the real industrial conditions and after long-term exposure to steam oxidation conditions in a thermal power plant.

Both the effect of the grain size in austenite and the role of shot peening on steam oxidation are discussed.