The paper presents the assessment results of probability of detection for damages in mechanical structures conducted with a Structural Health Monitoring (SHM) system based on the measurements of electromechanical impedance. The research was carried out with both numerical models and real-life mechanical components. The results of laboratory tests performed in operational conditions for a bolted pipeline connection confirmed usefulness of both the applied monitoring method and the SHM system. The hit/miss and signal response statistical approaches were employed to gain insight into the specific SHM system reliability.