The Main Feedwater System of Fuqing nuclear power plant is composed of three electric pump sets arranged in parallel with 50% capacity to provide the required Feedwater for the secondary side of steam generator. Under normal conditions, two pumps are in operation, one is standby, and three pumps can be switched at will. When one of the two running electric feed water pump sets trips, the electric feed water pump set in standby state will start quickly. If the equipment has problems, it will seriously affect the safe and reliable operation of the unit.

After the leakage defect of the warm-up pump pipe downstream of the warm-up pump stop valve in train C of the main feed water pump system of Hualong unit was found, through the disassembly inspection, it was found that there were many surface corrosion pits in the downstream pipeline of the throttle orifice plate. In this paper, through the physical and chemical analysis of the pipeline composition, organization, non-metallic inclusions, surface quality, macro and micro morphology, etc, At the same time, combined with the operating conditions of the pipeline, analyze the causes of the defects, judge the defects caused by the medium vaporization caused by the excessive throttling of the throttle orifice, and give effective treatment measures. Through these relevant measures, the corrosion rate of the warm-up pump pipe is reduced and the operation reliability of the important equipment of the unit is improved.

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