A wave finite element (WFE) strategy to predict and localize defects in networks of straight pipes with curved joints is proposed. This involves estimating the times of flight taken by some narrow wave packets to get transmitted through or reflected by a coupling element that could represent either a joint or a defect. The ansatz proposed here is to define these times of flight from the frequency derivatives of the arguments of the scattering matrix of the coupling element. Also, the times of flight taken by wave packets to travel along a certain pipe can be classically obtained from the analysis of the group velocities. By comparing the theoretical expressions of the times of flight with those recorded in a network of pipes at some measurement point, it becomes possible to localize a defect with accurate precision and, also, to have a physical insight about the kind of waves which are transmitted through a joint and reflected by a defect (pathways). Numerical experiments are carried out which highlight the relevance and applicability of the proposed approach.