Through test analysis and theoritical calculation for over-temperature burst of drain pipeline from high-pressure(HP) cylinder of the steam turbine for 300 MW unit in one Power Generation Co Ltd

the causes leading to a special phenomenon

i.e.the severe over-temperature burst occurred on the drain pipeline under condition of the exhaust steam temperatrue from HP cylinder of the steam turbine was far lower than the service temperature of 12Cr1MoV steel used in the hydraulic pipeline

has been explained.The effect of rubbing heat due to supersonic steam flow resulted from special structure of the drain pipeline from HP cylinder is far larger than the effect of convective heat exchange

finally resulting in over-temperature burst of the pipeline.The related tests and calculation theory provide basis for preventing this kind of pipeline burst due to its special structure.