This paper discusses the application of transient test-based techniques (TTBTs) for fault detection in the Trieste subsea pipeline, managed by AcegasApsAmga SpA. The study focuses on the analysis of pressure signals acquired during field tests to identify wall deterioration and other anomalies. The transient numerical model, based on 1-D equations governing transients in elastic pressurized pipelines, is used to simulate the transient response of anomalies such as leaks and wall deterioration. The analytical model evaluates the effect of these anomalies on the pressure signal. Field tests revealed pressure variations at sections M and P, which were analyzed using wavelet analysis to determine the arrival time of pressure waves. The numerical simulation of the experimental pressure signals showed discrepancies with the actual signals, indicating the need for further refinement. The trial-and-error procedure identified three distinct anomalies, with the first two attributed to wall deterioration rather than leaks. Diver inspections confirmed substantial wall deterioration in sections A1 and A3. The study concludes that TTBTs are effective for fault detection in subsea pipelines, but further improvements are needed in the numerical model to better align with experimental results.This paper discusses the application of transient test-based techniques (TTBTs) for fault detection in the Trieste subsea pipeline, managed by AcegasApsAmga SpA. The study focuses on the analysis of pressure signals acquired during field tests to identify wall deterioration and other anomalies. The transient numerical model, based on 1-D equations governing transients in elastic pressurized pipelines, is used to simulate the transient response of anomalies such as leaks and wall deterioration. The analytical model evaluates the effect of these anomalies on the pressure signal. Field tests revealed pressure variations at sections M and P, which were analyzed using wavelet analysis to determine the arrival time of pressure waves. The numerical simulation of the experimental pressure signals showed discrepancies with the actual signals, indicating the need for further refinement. The trial-and-error procedure identified three distinct anomalies, with the first two attributed to wall deterioration rather than leaks. Diver inspections confirmed substantial wall deterioration in sections A1 and A3. The study concludes that TTBTs are effective for fault detection in subsea pipelines, but further improvements are needed in the numerical model to better align with experimental results.