Model Based Approach To Identify Optimal System Structures and Maintenance Policies for Safety Interlocks with Time-Varying Failure Rates

Abstract

In order to mitigate the detrimental outcomes of accidents in the modern chemical plants, it is a common practice to install safety interlocks on processes operated under hazardous conditions. A generic mathematical programming model has already been developed in the past for simultaneously stipulating the optimal interlock structure and the corresponding maintenance policies of a given process. This conventional formulation is improved in the present study by relaxing a constraining assumption, that is, the failure rate of every embedded component is constant. Instead of the exponential distribution, the more realistic Weibull distribution is incorporated in the modified model to characterize the time to failure of every embedded component. Consequently, this proposed practice could facilitate identification of more elaborate timedependent inspection schedules and also alarm logics. Two examples are provided to demonstrate the feasibility and effectiveness of the proposed approach.

Optimization of Multilayer Standby Mechanisms in Continuous Chemical Processes

“…Note that another class of protection mechanisms may also be present in the chemical plants for an entirely different purpose, i.e., emergency shutdown. Since the related issues have already been addressed thoroughly, e.g., see Liang and Chang, 2 Liao and Chang, 3 Wibisono et al, 4 and Lepar et al, 5 this latter class is not discussed in the present paper.…”

“…Liang and Chang developed an integer programming model to optimize the structures and maintenance policies of multilayer protective systems, while Liao and Chang later amended this model so as to extend its applications to the multichannel ones. Wibisono et al further considered components with time-dependent failure rates in this model by incorporating the Weibull distribution. Although successful applications of the above models have been reported extensively, they still cannot be directly applied to the standby systems.…”