This study introduces three generalized component importance measures for identifying critical components of heterogeneous substrate infrastructure networks. The proposed metrics are applied to a realistic European gas transmission network and different sets of critical components are obtained. The criticality of gas supply and the resilience of demand nodes are also analyzed based on the multiple sources and sinks maximum flow problem. The weakness of the network structure under some particular supply disruption scenarios is highlighted. These results of this type of analysis can be of great use in supporting network design and operation, e.g., for deciding which components should be protected and/or upgraded under a limited budget.