The performance of an industrial system has great significance in recent years due to competitive environment and overall operating and production costs. When the performance of a large complex system or process plant such as chemical, paper, textile, thermal, paint, fertilizer, dairy, sugar etc. plant is low, efforts are needed to improve the performance by reducing the failure rate or increasing the repair rate for each component or subsystem of the system. The performance of an industrial system or process plant can be quantified in terms of the reliability or availability if the operating system is modeled mathematically and analyzed in real working conditions. The reliability and availability analysis has helped to identify the critical subsystems or components of the system that need more attention for improvement.