The Effect of Heat Flux on the Steam Oxidation Kinetics and Scale Morphology of Low Alloy Materials

摘要

Next generation boiler design is driven by the need to increase the efficiency both for carbon reduction and capture. This is pushing conventional materials to their limits both in terms of strength and oxidation resistance. Conventionally, corrosion tests are performed on simple test coupons under isothermal conditions and whilst this does provide a guide on material performance it is somewhat simplified and removed from reality. Given that so much of the boiler is operated under conditions of heat transfer it seems appropriate to evaluate the degradation of candidate materials under heat flux conditions rather than simply isothermal conditions. With this in mind a test method has been designed to perform such a test on tubular specimens and has been demonstrated using both laboratory air and steam as the cooling medium. This initial comparison of the tubular heat flux specimens and flat isothermal specimens of 15Mo3 showed that there was a clear and significant effect from the presence of a thermal gradient across the tube wall, with an increase in the oxidation kinetics and a change in the oxide morphology.The following paper describes the design of the heat flux test and the results of initial work on 15Mo3 under air and steam conditions. In addition details of further work on oxides formed on 2 1/4Cr material in the laboratory under both heat flux and isothermal conditions is presented.