Modelling oxide scale fracture

Abstract

In the present paper the approaches to modelling scale failure described in EPRI report FP 686 are compared to a more recent approach based on micromechanical considerations. The latter requires a detailed analysis of the stress situation in the oxide/metal system and of the “quality” of the oxide scale and scale/metal interface, respectively. It turns out that a considerable number of model equations exists describing the role of oxide stresses, including such from cooling and surface or component geometries, and the role of physical defects, e.g. pores, voids, microcracks, etc. Additionally, these equations need material property data, such as fracture toughness or energy and elastic moduli, which sometimes can be found in the literature. In the final step it is proposed to combine the EPRI approach with the more recent micromechanics based models leading to a powerful tool for a detailed assessment of failure susceptibility of oxide scales. The general “EPRI diagram” can serve as a foreground diagram behind which the more sophisticated equations of the micromechanics approach are hidden. In order to enable wide use of this extended model, however, a number of additional input data are needed.

Keywords:

• modelling oxide scale fracture