On the thermal origin of the antagonistic and synergistic effects of fretting and crevice corrosion processes in multi-phase flow environment

摘要

Heat exchange systems usually operate in multi-phase environment and compose of non-conforming structural components in contact. In addition to crevice corrosion, fretting corrosion damage may also take place at the contact interface as a result of flow-induced vibrations. Local nucleate boiling in the crevice region between contacted bodies causes an increase in the chemical concentration of the solute flowing in this region. This in turn accelerates the crevice corrosion damage. Development of reliable thermal models is, therefore, critically needed for reliable design and safe operation of these heat exchange systems. In this paper, a system approach is adopted to accurately predict the onset of nucleate boiling and accelerated crevice corrosion near the contact region of non-conforming bodies. The proposed methodology recognizes the nonlinear nature of the process and the presence of multi-dimensional closed loop interactions. On one level, there is interaction between the temperature field and the boiling process, through the changes in the conditions of heat transfer at adjacent water-cooled surfaces. On another level, this methodology allows due consideration of the mutual interactions between the crevice and the fretting corrosion processes. The thermal model accounts for the volumetric effect of the thermal constriction resistance R_c and allows evaluating the thermal barrier effect caused by the increase in the R_c due to surface coating and/or fretting corrosion. Analysis of the results indicated the significance of modeling the nonlinear behaviour of the system for accurate prediction of the extent of local nucleate boiling in the crevice region. The results also indicated that the increase in the R_c with surface coating and/or fretting corrosion can cause the crevice corrosion process to be self-limiting.