Created on:2021-07-19 13:47

Maintenance of circulating water system of 300MW Nuclear Power Unit_ Overview of butterfly valve

Maintenance of circulating water system of 300MW Nuclear Power Unit_ Overview of butterfly valve

Six circulating water pumps are installed in the circulating cooling water system of a 300MW Nuclear power unit, and each pump outlet is equipped with a hydraulic butterfly valve. Each hydraulic butterfly valve and the corresponding circulating water pump adopt linkage control, that is, when the circulating water pump starts, the butterfly valve opens and the pump stops, the valve closes. Butterfly valve is not only isolation valve, but also outlet check valve. Each butterfly valve is controlled by an independent hydraulic system. The pressure oil acts on the upper part of the piston of the lifting hydraulic cylinder, and the butterfly valve is opened by the working stroke of the piston rod, which is locked by the locking pin at the front end of the locking hydraulic cylinder; The system solenoid valve controls the valve to close by the gravity of the heavy hammer on the swing arm of the valve stem after the oil pressure of the hydraulic cylinder is removed.

Since the installation of the hydraulic butterfly valve, there have been many defects. After many times of debugging, it can not be put into normal use, resulting in the No. 6 circulating pump system can not run, seriously affecting the safety of the unit. During the overhaul of nuclear power unit, the manufacturer required to carry out technical transformation on No.6 hydraulic butterfly valve to make it operate normally.

After receiving the work item, the previous failures of No. 6 hydraulic butterfly valve were summarized, counted and analyzed one by one. According to statistics, the main faults are as follows:

① The leakage of the hydraulic system is serious, and the oil level of the oil supply tank is low when the system runs for 3 ~ 4H;

② Internal leakage of hydraulic system components, system pressure can not be maintained, frequent action of pressure switch to start hydraulic pump to supplement pressure;

③ When the valve is opened, the system vibrates greatly, and the system oil pressure is unstable, and the oil pressure fluctuates greatly;

④ When the oil pressure drops, the hydraulic pump can't stop automatically, which causes the oil temperature in the oil tank to rise and the oil quality to deteriorate.

After obtaining the relevant data, the hydraulic system components and actuators are tested and inspected, and the frequency and causes of the faults are analyzed item by item. The statistical results are shown in the table below.

 

Frequency and cause statistics of faults

Serial number

故 障 统 计

故 障 原 因

所占总故障比例%

1

系统渗漏、油位低报警

液压缸渗漏严重

系统接头渗漏

65%

2

系统油压低、泵不出力或出力不足

溢流阀、电磁阀、逆止阀内泄

5%

3

泵补压启动频繁、补压达不到定值,不能自停

系统渗漏,溢流阀、电磁阀、逆止阀内泄,压力开关定值漂移

15%

4

系统振动大,管道及执行机构有异声

系统有空气,压力不稳,蓄能器氮气压力不足

5%

5

供油箱油温高报警

油值恶化

溢流阀内漏,泵在系统内大流量循环造成油温升高

5%

6

其他故障

 

5%

 

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