APPROXIMATE ANALYTICAL ESTIMATE OF RELIABILITY INDICES FOR AGEING FACILITIES OF WATER SUPPLY AND SEWER SYSTEMS

Abstract

Introduction. The paper addresses characteristic features of methodological approaches to solving engineering reliability problems associated with aging facilities of water supply and sewer systems in large cities. It is noted that, in case of longlived facilities, well-known procedures for solving practical tasks are not applicable due to non-stationarity (in terms of reliability) of such facilities. Methods. A real non-stationary (“aging”) facility (object) is formally replaced by its virtual stationary analog with a constant failure rate, which can be determined based on the condition of equality between reliability functions of those real and virtual objects for a particular operating time. Mean operating time to failure of the virtual object is chosen as such point on the time-axis. A corresponding equation is obtained and solved for the unknown variable that, as a result, can be expressed in terms of “aging law” for a real non-stationary object. An approximation error is estimated analytically for a linearly aging object. It is demonstrated that in case of a real combination of “aging law” parameters, this error does not exceed 4–5%, which is quite acceptable for engineering calculations. Results. The authors develop a procedure for the approximate substitution of a non-stationary object by a stationary one (stationarization) where the failure flow is expressed in terms of reliability function coefficients of a real aging object. This procedure makes it possible to use well-known methods of solving reliability problems of stationary objects when analyzing non-stationary objects. Conclusion. The proposed procedure of approximate estimate for basic reliability indices of non-stationary objects is convenient for practical use.