Cause and prevention measures for Cracking of Surfacing Layer on Sealing Surface of Main Steam Safety Valve Disc in Nuclear Power Units

TANG Heng; YIN Bangyao; WANG Qi; DENG Jiangyong

doi:10.7512/j.issn.1001-2303.2024.04.09

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Cause and prevention measures for Cracking of Surfacing Layer on Sealing Surface of Main Steam Safety Valve Disc in Nuclear Power Units
Vol. 54, Issue 4, Pages: 63-70(2024)
Received：25 July 2023，

Revised：2023-10-16，

Published：25 April 2024
DOI： 10.7512/j.issn.1001-2303.2024.04.09
稿件说明：

移动端阅览

汤恒，银帮耀，王琪，等.核电机组主蒸汽安全阀阀瓣密封面堆焊层开裂原因分析及预防措施［J］.电焊机，2024，54（4）：63-70. DOI： 10.7512/j.issn.1001-2303.2024.04.09.

TANG Heng, YIN Bangyao, WANG Qi, et al.Cause and prevention measures for Cracking of Surfacing Layer on Sealing Surface of Main Steam Safety Valve Disc in Nuclear Power Units[J].Electric Welding Machine, 2024, 54(4): 63-70. DOI： 10.7512/j.issn.1001-2303.2024.04.09.

摘要

某核电厂大修期间对VVP116VV安全阀进行解体检查，发现阀瓣密封表面堆焊层存在20多条裂纹缺陷。通过宏观检查、化学成分分析、金相检验、硬度测试、残余应力分析、扫描电镜断口分析及能谱分析等方法分析阀瓣密封面堆焊层开裂的原因。结果表明：阀瓣密封面堆焊层的Fe含量明显偏高，表明稀释率过大，这与堆焊工艺控制不当（焊接热输入过大、热处理控制不当）有关。焊接热输入过大引起堆焊层残余应力偏高是开裂的主要原因；层间温度控制不当及焊后热处理不充分可能是促成堆焊层开裂的因素。并根据开裂的原因分析结果给出了处理建议，可以为其他机组的同类问题提供参考。

Abstract

During the overhaul of a certain nuclear power plant

the VVP116VV safety valve was disassembled and inspected

and it was found that there were more than 20 crack defects in the welding layer on the sealing surface of the valve disc. Analyze the reasons for the cracking of the valve disc sealing surface surfacing layer through methods such as macroscopic examination

chemical composition analysis

metallographic examination

hardness testing

residual stress analysis

scanning electron microscopy fracture analysis

and energy spectrum analysis. The results indicate that there is a problem of high dilution rate in the surfacing layer of the valve disc sealing surface. Analysis suggests that it is related to improper control of the surfacing process (excessive welding heat input

improper heat treatment control). The main reason for the cracking of the surfacing layer is the high residual stress in the surfacing layer caused by excessive welding heat input. Improper control of interlayer temperature during the welding process and insufficient post weld heat treatment may be contributing factors to the cracking of the surfacing layer. According to the result of cause analysis

the disposal suggestions are given to provide reference for similar problems of other units.

关键词

Keywords

references

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