Probabilistic approach of reliability evaluation for the tubular elements of the chemical equipment according to technical state changing

Abstract

During the operation of chemical equipment, its technical condition, operating modes and operability change. Such phenomena are typical for the main element of chemical equipment - tubular elements, which must have the required strength, ensure the transportation of the working medium and the transfer of heat between the working medium. During the operation of tubular elements the wall thickness decreases, deposits appear on them, the wall roughness and the flow area change. The parameters that affect the change in the technical state are probabilistic in nature and can vary over a wide range. As a result, the operability of both tubular elements and the equipment in which they are installed decreases.To evaluate the performance of tubular elements under conditions of changes in their technical state, it is proposed to use three functioning criteria: strength, temperature and hydraulic. The strength criterion has the following meaning: the internal working pressure must not exceed the tolerance one; temperature criterion – the temperature of the working medium inside the tubular element must be within the specified range; hydraulic criterion – the pressure drop must not exceed the tolerance value. It has been developed a probabilistic mathematical model that allows one to determine the criterion parameters under the assumption that the influencing factors have a normal distribution law and are described by their mathematical expectation and standard deviation.The proposed method allows, with a given level of reliability, to substantiate the design parameters of tubular elements during their design taking into account changes in the technical state during operation.