AcegasApsAmga SpA, of the Hera Group, manages the water systems of Padova and Trieste. Within the water supply system of Trieste, the submarine transmission main (TM) plays a crucial role. In fact it supplies not only the city of Trieste but also the Carsico plateau. Such an iron DN1330 pipe has a length of about 18 km and conveys 700 L/s with a steady-state pressure equal to 7 - 10 bars according to the elevation.

At present divers execute the inspection of the Trieste TM. With the aim of implementing a systematic inspection procedure, AcegasApsAmga SpA decided to proceed with a transient test-based technique (TTBT), which requires small pressure waves to be injected into the test pipe to detect anomalies. Because of the large diameter of the pipeline, the installed valves cannot be closed as fast as required to generate small amplitude sharp pressure waves, which allow precise defect localization. As a consequence, a small side valve has been installed at both the end sections of the pipeline to generate safe transients.

In this paper the first results of the executed transient tests are reported and discussed.