Analysis of effectiveness of compressor design stage in solving reliability problems

Abstract

Calculation of compressor design reliability is based on structural reliability schemata (SRSs), employing two approaches: use of the reliability characteristics of actual compressor components or use of arbitrary design elements of the first and second types. As we know [i], from the standpoint of reliability a compressor constitutes a combination of arbitrary design elements of two types: those describing the working process in the compressor and those describing the status of compressor components and assemblies as a function of the action of mechanical and other factors that are not taken into account in describing the compressor working process (strength, strain, etc.). Arbitrary design elements of the first type include throughput, power consumed by the compressor, vibratory and acoustic characteristics, etc. Moreover, a compressor can be represented by a collection of real parametric and functional elements from the reliability standpoint [I]. A parametric element can have one or more basic operating characteristics that describe the working process in the element and one or more auxiliary working characteristics (strength, strain, wear, etc.) that describe the status of the element (assembly) and its components under the influence of mechanical and other factors. Thus, a parametric element is a combination of arbitrary design elements of both types in terms of reliability (as in the case of the compressor as a whole). Unlike a parametric functional element, a compressor can have just one or only a few main working characteristics, including strength, strain, wear, etc. A functional element is thus a combination of arbitrary design elements describing its basic working characteristics, which are series-connected in terms of reliability. Calculation of reliability from arbitrary design elements of the first and second types entails the use of a parametric model that takes into account the influence of gradual failures~ the influence of sudden failures must be allowed for by a separate component in the overall reliability estimate. We will consider the feasibility of applying these approaches to calculation of compressor reliability during different design stages. During the engineering proposal stage: the results of thermodynamic calculations for the compressor as a whole can be used to determine the probability of fault-free compressor operation with respect to throughput and power consumption (or, more precisely, its parametric component for gradual failures, i.e., a design element of the first type)~ here the draft contains none of the data needed for determination of the reliability component for the second type of design element (auxiliary working characteristics, i.e., strength, wear, etc.)~ sudden failures can be taken into account by utilizing data for an analogous compressor (which merely serves as a guideline, since the compressor under analysis has still not been fully worked out in terms of design) or the required failure-free operating parameters for the compressor being analyzed (rated failure-free operating time and mean time between failures)~ the estimate is also just a guideline in this case. At the working design stage: the refined data from the thermodynamic calculations can be used to obtain the sharpened parametric component of the initial probability of failure-free compressor operation from the main operating characteristics (throughput and power consumption); this constitutes an arbitrary design element of the first type in the compressor SRS; available design materials and the results yielded by computation of operating parameters for a number of important compressor assemblies and components can be employed to determine their parametric contribution to the probability of failure-free operation: it