The relevance of the research is caused by the necessity to determine the residual resource of the equipment with a sufficient degree of accuracy and in various circumstances. The development of mathematical models for assessing the mechanisms of damage accumulation and the actual state of the equipment will allow predicting the development of changes in the state of the object, considering the established patterns of damage mechanisms, and determining the moment of occurrence of the limit state. The aim of the research is to propose a method for assessing the residual resource of heat exchangers, considering expert intuitive-logical analysis of the problem with a quantitative assessment of judgments and processing of results. Objects: heat exchangers, expert conclusions on heat exchangers used in oil refining. Methods: Kullback–Leibler informative model, showing the degree of informativeness of individual parameters to the degree of discrepancy between the two classes of objects, diagnosing residual resource for the development of corrosion damage, diagnosing residual resource of equipment related to changed parameters of its technical condition. Results. The paper sets the task to assess the service life of the heat exchanging equipment after diagnosing on the allowed technical parameters depending on the total effect of the parameters of the technical condition of the equipment for oil and gas processing and petrochemistry. 10 technical and technological indicators of heat exchangers were selected, and the evaluation was performed by using such an indicator as the residual service life of heat exchangers. The authors developed a mathematical model, calculated diagnostic coefficients and informativeness of the indicator for each period accepted by the expert. An algorithm for estimating the residual service life of heat exchangers based on the Kullback informativeness measure is proposed. Estimates of the residual resource, out of the constructed model are shown. Conclusions about the rationality of using the proposed algorithm for solving problems of this type are made.