Reliability and availability evaluation for highly meshed network systems: status of the art and new perspectives

The paper addresses the problem of the reliability and availability assessment of meshed network systems, such as gas or heat distribution systems. An introduction highlights the specific associated problems related to the structural complexity and to the dynamic character of these systems. An approach merging reliability indexes and fault trees is described with reference to a real application consisting of a district heating network in Northern Italy. The results of the study, together with the pros and cons of the approach, are discussed. A critical analysis follows, where possible alternative approaches for future developments of the research project are described and evaluated. The analysis shows the attitude of the indexes approach to provide overall information regarding the reliability and availability of the networks but leads to consideration of new approaches for the assessment of the reliability and availability of single nodes; this could be addressed by substituting the fault tree approach with more flexible and efficient techniques such as the cut set method, based on graph theory, or Monte Carlo simulation.