Due to their length and often complex construction, pipelines are difficult to diagnose and monitor its technical condition. It is particularly difficult to detect small leaks of medium and their location. The article shows the basics of the leakage detection and evaluation method based on standard signals recorded during the operation of the pipeline and weak interaction signals from the device attached to the pipeline – corrective element. Auto and cross correlations of these signals were used to determine the diagnostic models in the form of amplitude gain (A2) and phase shift (Φ), Gradzki et al. (2018, 2019).