Introduction

Since the Industrial Revolution, maintenance of engineering equipment in the field environment has been a challenging issue. Although over the years impressive progress has been made in maintaining equipment in the field environment, maintenance of equipment is still a challenging issue with regard to factors such as cost, complexity, competition, and size. Each year billions of dollars are spent to maintain engineering systems throughout the world. For example, U.S. industry spends over $300 billion on plant maintenance and operation annually [1]. It is estimated that about 80% of this amount is spent to rectify the chronic failure of systems, machines, and humans.