Abstract:

The current of fire-resistant oil pump was increased suddenly and the oil pressure was descended in a 600 MW supercritical unit. Based on the failure cause investigation， it was suggested that the accident was caused by the servo valve leakage of high pressure control valve. The fire-resistant oil and the material of servo valve were analyzed by scanning electron microscopy （SEM） and energy spectrum analysis， as well as chemical compositions. The results show that the leakage of servo valve is due to the interaction of pitting corrosion and wear， which are caused by the long-term excess-standard of acid value and high chloride ion content of the fire-resistant oil. Finally， some improvement measures and suggestions were proposed according to the existing problems.

Key words: 600 MW supercritical unit, fire-resistant oil, servo valve, pitting corrosion, wear