The insufficient output and the abnormal gradual pressure rise at the first stage occurred after the first overhaul in a 630MW supercritical unit.On the basis of monitoring variation trend of the thermodynamic parameters and its performance

the fouling fault in flow passage of the HP steam turbine was diagnosed.Against this problem

several countermeasures were taken during the second overhaul

such as boiler acid cleaning

sand blasting to turbine blades and condensate oxygenated treatment to inhibit the flow accelerated corrosion(FAC).After the improvement

the fouling problem in flow passage of the steam turbine was solved

the first stage pressure returned to normal and the unit output was increased.