MATHEMATICAL MODELING OF PITTING RESISTANCE IN 06XH28МДТ ALLO-HEAT EXCHANGERS EXPOSED TO CIRCULATING WATERS

Abstract

Purpose. The aim of the study is to develop mathematical models that describe the dependences of critical pitting temperatures of 06ХН28МДТ alloy (analogous to AISI904L steel) in model circulating waters with pH 4...8 and chloride concentration from 350 to 600 mg/L. Research methods. The developed mathematical models are based on multivariate linear regressions of the first order and multivariate quadratic regressions with a combination of features. Results. It has been established that the critical pitting temperatures of the 06ХН28МДТ alloy increase with increasing pH of model circulating waters, Ni, Mo content, volume of titanium nitrides, and decreasing chloride concentration in the medium, Cr content within the standard, and average austenite grain diameter. Scientific novelty. Based on the established dependencies between the critical pitting temperatures of the 06ХН28МДТ alloy and its chemical composition within the standard and structural heterogeneity, the mechanisms of their influence on the pitting resistance of this structural material in recycled industrial waters were developed. It was found that the size of inclusions of titanium nitrides and oxysulfides in the alloy does not affect the probability of the formation and growth of stable pitting in their vicinity in chloride-containing media. Practical value. To apply the developed mathematical models to the selection of the most resistant to pitting in recycled industrial waters of 06ХН28МДТ alloy melts and to predict their pitting during the use of heat exchangers have been offered.