Preliminary calculations of erosion wear resulting from exfoliation of iron oxides in austenitic superheaters

Based on laboratory testing and experience related to boiler operation, this paper presents the phenomenon of oxide exfoliation (spallation) from the surface of the tubes of superheaters made of austenitic alloys. A computational model is proposed to determine the rate of erosion of the boiler and the turbine components by solid particles carried by steam. A method is developed to calculate both the mass of iron oxides detached from the inner surfaces of the superheater tubes and the erosion time. Using the computational models developed, the rates of erosion of the reheater elbow and the turbine control valve are determined for certain exemplifying conditions. The calculation results indicate that a condensate purification system must be used because a noticeable loss of material might occur, especially in the turbine components, even at a single flow of steam contaminated with exfoliated iron oxides. Therefore, the exfoliated particles must be eliminated from the power plant cycle as soon as possible.

► Exfoliation of the first, relatively thick, epitactic layer poses operational hazard.
► Exfoliation is highly dependent on the wall temperature along the coil length.
► It is necessary to minimise differences in thermal loads of superheater coils.
► It is necessary to minimise differences in the steam temperatures at their outlet.