The failure mechanism of steam pipe in boiler of a liquid natural gas(LNG)gas-steam combined cycling unit was investigated.The results showed that

the position and time of failures occurred on steam pipe of the LNG gas-steam combined cycling unit were regular.Peak load operation with daily startup and stop of this power plant led to sharp varying load conditions

causing large thermal stress on inner and outer wall of the boiler components.Furthermore

large variation of the thermal stress resulted in fatigue damage in stress/strain concentration area.Besides

during the unit stop process for peak operation

water was easily accumulated inside the components

causing pitting corrosion.When the outside tube wall temperature was lower than the flue gas dew point

stress corrosion may occur.Therefore

fatigue and corrosion are the main failure mechanisms of steam pipes in the LNG gas-steam combined cycling units.