Определение вероятности обеспечения номинального режима работы магистрального продуктопровода с учетом процесса старения перекачивающих агрегатов

Abstract

Aim. The article provides a method and a formula for calculation of probability of nominal operating mode for main product pipeline (MPP) – further as the text goes, MPP availability function – with consideration of ageing of its pumping units which are periodically maintained in accordance with a normative service strategy. This availability function is determined in the following assumptions: 1. MPP is composed of two basic parts: passive part – high reliable line part; and active part including pump stations which ensure nominal operating mode for the product’s pumping-over. MPP may contain any finite number of pump stations. 2. Each pump station includes the system of main pumping units (MPU system) which are active elements of the station, instrumentation and control, pipeline accessories and shutoff valves, as well as other essential technological equipment. MPU system is the part of pump stations ensuring nominal conditions for the oil products pumping-over and which is usually consists of four homogeneous MPUs. 3. MPU arrangement makes it possible to bring each working unit into standby, and substitute it with any standby unit. 4. A required nominal mode for MPP operation is determined by hydraulic and cost calculations as the result of which a required operating mode is indicated for each pump station. For each station the number of MPU is indicated which must be in a working order, and the rest MPU shall be either in standby, or under restoring repair performed in accordance with a normative service strategy. Thus, nominal mode of MPP operation is ensured by the respective modes of pump stations, which with regard to pumping units are determined by the number of active MPUs. Analysis of statistics related to the failures of pumping units maintained in accordance with a normative service strategy makes it possible to define the units’ failure rate in each interval between overhauls. In particular, failure rates are increasing on the respective intervals which means the ageing of units with their operation. Then the method for calculation of availability function for any pumping unit within the scope of MPP is offered. Initial conditions and differential equations are written to find an availability function for each MPU system at pump stations, obtained using the “death and reproduction” scheme. Basic results of calculations per each of three sequential intervals between overhauls are represented in form of graphs that show the influence of ageing of the units on the values of MPU availability function at a pump station: values of derivatives of availability function are sequentially decreasing for the respective times counted from the start of each recurrent overhaul. The expression to calculate availability function of MPP with several pump stations is also provided. The results of calculation of the availability function can serve as the grounds for modernization of a normative periodic strategy on order to increase the probability of MPP nominal mode, as well as other technical and economic performance indicators of MPU systems, in particular, energy efficiency indicators. In particular, it is pointed out that certain types of non-periodic service strategies, built on the basis of a normative strategy may significantly increase the values of indicated.