Joint condition-based maintenance and load-sharing optimization for two-unit systems with economic dependency

Michiel A.J Uit Het Broek,Ruud H Teunter,Bram De Jonge,Jasper Veldman

doi:10.1016/j.ejor.2021.03.044

Michiel A.J Uit Het Broek, Ruud H Teunter + Show 2 more

Open Access

https://doi.org/10.1016/j.ejor.2021.03.044

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Abstract

Many production facilities consist of multiple and functionally exchangeable units of equipment, such as pumps or turbines, that are jointly used to satisfy a given production target. Such systems often have to ensure high levels of reliability and availability. The deterioration rates of the units typically depend on their production rates, implying that the operator can control deterioration by dynamically reallocating load among units. In this study, we examine the value of condition-based load-sharing decisions for two-unit systems with economic dependency. We formulate the system as a Markov decision process and provide optimal joint condition-based maintenance and production policies. Our numerical results show that, dependent on the system characteristics, substantial cost savings of up to 40% can be realized compared to the optimal condition-based maintenance policy under equal load-sharing. The structure of the optimal policy particularly depends on the maintenance setup cost and the penalty that is incurred if the production target is not satisfied. For systems with high setup costs, the clustering of maintenance interventions is improved by synchronizing the deterioration of the units. On the contrary, for low setup costs, the deterioration levels are desynchronized and the maintenance interventions are alternated.

Highlights

Many production facilities consist of multiple units that are jointly used to satisfy a production target
Our results show that condition-based load-sharing improves the effectiveness of condition-based maintenance policies, and that its effectiveness heavily depends on the degree of overcapacity
In practice, the reliability of such systems is often improved by including a redundant unit, which we model by setting the production target equal to the capacity of a single unit κ = 1.0

Summary

Introduction

Many production facilities consist of multiple units that are jointly used to satisfy a production target These units deteriorate due to load and stress caused by production and eventually require maintenance in order to keep the system in, or bring it back to, an operating condition. Many studies aim to reduce these costs by developing condition-based maintenance policies and show that such policies reduce costs while improving availability and productivity Another option to improve the cost efficiency of production facilities is to control the deterioration of its units by adopting condition-based production policies (Uit het Broek et al, 2019a,b). Such policies exploit the relation between the production rate and the deterioration rate by dynamically adjusting the production rate based on condition information. Optimal maintenance policies for multi-unit systems are often more advanced than for single-unit systems because of the various types of dependencies that exists between

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