This paper, the first of a series, focuses on the application of transient-test-based techniques (TTBTs) for fault detection in subsea pipelines (SPs), specifically the Trieste SP managed by AcegasApsAmga SpA. The Trieste SP, characterized by its length (18 km), large diameter (1.3 m), and lack of branches, provides an ideal scenario for assessing the feasibility and reliability of TTBTs. The paper outlines the challenges associated with inspecting SPs, which are vulnerable to damage from both human and natural causes, and highlights the need for reliable and cost-effective inspection technologies. The authors discuss the selection of appropriate maneuvers to generate pressure waves and the sequence of actions required for effective fault detection. They also review existing fault detection technologies and their limitations. The performance of the proposed procedure is evaluated based on the stability of the pressure regime before the execution of the transient test. The paper details the preliminary survey to evaluate the system's response to maneuvers, the hydraulic characterization of the maneuver valve, and the field procedure breakdown. The results of the transient response of the Trieste SP to the field procedure are presented, emphasizing the importance of precise timing and sequence of maneuvers to ensure the effectiveness of TTBTs. The companion paper will detail the fault detection procedure and results.This paper, the first of a series, focuses on the application of transient-test-based techniques (TTBTs) for fault detection in subsea pipelines (SPs), specifically the Trieste SP managed by AcegasApsAmga SpA. The Trieste SP, characterized by its length (18 km), large diameter (1.3 m), and lack of branches, provides an ideal scenario for assessing the feasibility and reliability of TTBTs. The paper outlines the challenges associated with inspecting SPs, which are vulnerable to damage from both human and natural causes, and highlights the need for reliable and cost-effective inspection technologies. The authors discuss the selection of appropriate maneuvers to generate pressure waves and the sequence of actions required for effective fault detection. They also review existing fault detection technologies and their limitations. The performance of the proposed procedure is evaluated based on the stability of the pressure regime before the execution of the transient test. The paper details the preliminary survey to evaluate the system's response to maneuvers, the hydraulic characterization of the maneuver valve, and the field procedure breakdown. The results of the transient response of the Trieste SP to the field procedure are presented, emphasizing the importance of precise timing and sequence of maneuvers to ensure the effectiveness of TTBTs. The companion paper will detail the fault detection procedure and results.