Abstract:For gas steam combined cycle units, the steam turbine is a very important main equipment that directly affects the safety and economy of the unit.This article studies a typical case of turbine shutdown caused by damage and fracture of the last stage blades due to water erosion. It deeply analyzes the causes of blade fracture, summarizes the main problems exposed, and proposes improvement measures, providing a warning for the safe and stable operation of gas steam combined cycle units in the future.The analysis shows that when unit in deep peaking regulation,the vortex zone is formed at the root of the last stage blade of the steam turbine, and the steam flow impinges on the root of the blade in reverse direction, the backflow steam carrying water droplets impinges on the exit edge of the high-speed rotating last stage rotor blade, causing water erosion on the exit edge of the rotor blade；When the steam turbine blade rotates at high speed, the root area of the blade bears a larger centrifugal force and inertial force, and the working environment of the last several stages of the blade is worse, and the moisture content of the steam is greater, under cyclic loading, fatigue cracks may appear on the blade surface where the corrosion pits are more serious, which may lead to blade fracture.