Reliability: Modeling, Prediction, and Optimization

CHAPTER 16

Maintenance of Unreliable Systems

16.1 INTRODUCTION

As mentioned in Chapter 1, all man-made systems are unreliable in the sense that their performance deteriorates with age and/or usage and they ultimately fail when they are unable to perform their required function under specified operating conditions. Deterioration and failure have a negative consequential effect on the buyer (be it an individual, a business, or a government agency) and are influenced by several factors, some under the control of the manufacturer (e.g., design, manufacture) and others under the control of the buyer (e.g., operational environment, maintenance).

Maintenance can be defined as actions to (1) control the deterioration process leading to failure of a system and (2) restore the system to its operational state through corrective actions after a failure. The former is called “preventive” maintenance and the latter “corrective” maintenance. Carrying out maintenance involves additional costs to the buyer and is worthwhile only if the benefits derived from such actions exceed the costs. From the buyer's viewpoint, this implies that maintenance must be examined in terms of its impact on system performance. Maintenance is of importance to manufacturers as well, since the ease and ability to carry out maintenance actions depends on the inherent characteristics of system design. This notion is defined through the concept of “maintainability.”

In this chapter we focus our attention on the maintenance ...