Abstract:() he start-up process of the thermal power plant"s thermal system pipelines, the drain water causes long-term scouring. Especially during the steam valve tightness test, the main steam pressure is high and lasts for a long time. The drain valves of the main and reheat steam pipelines remain open for a long time, and the drain water flows into the condenser, resulting in the scouring and thinning of components such as drain pipes, elbows, and drain manifolds, which then leads to leakage. During the start-up process, there is loud noise on the turbine side, making it impossible to judge the leakage situation. After the unit is started up normally and the drain valves are closed, air leaks into the condenser, affecting the vacuum of the condenser. This article discusses in detail effective leakage detection methods for similar situations, providing comprehensive technical guidance to solve such problems and ensure the safe operation of the unit and improve its economic efficiency.