Abstract: The availability of complex equipments is one of main indicators of measuring random failure during their operations, and to improve it is a crucial part to optimize their operations. Through in-depth analyzing the evolution of the state of the device under different maintenance strategies, the time dependent relationship among different states are studied. Then, the availability model of complex equipments based on Petri nets is built up. It describes both the degradation levels and the impact of different maintenance strategies on the whole operation. Reachability graph according to different maintenance strategies of device is analyzed, and then the isomorphic Markov chain model is also constructed. Through solving the steady state probability of different states, the availability under different maintenance strategies is calculated out. The optimal maintenance strategy is solved with the highest availability. Moreover the impact of the efficiency of preventive maintenance and failure repairment, on the availability and maintenance cost is also analyzed, and the trends are also discussed. Finally, the effectiveness of model and analysis method is verified by an example.

Key words: Availability, Complex equipment, Modeling, Stochastic Petri nets, alloying element, electrochemistry impedance spectrum, NaCl solution, rust layer, weathering steel