某电厂高温用止回阀阀瓣开裂原因

Reasons for cracking of the check valve disc for high-temperature use in a certain power plant

某电厂高温、高压水系统用止回阀发生泄漏现象,检查发现其阀瓣堆焊层发生开裂。采用宏观观察、化学成分分析、金相检验、硬度测试、残余应力测试、扫描电镜及能谱分析等方法分析了阀瓣开裂的原因。结果表明:阀瓣堆焊层的化学成分不合格,且存在疏松、气孔缺陷;阀瓣服役时受到介质冲击,外部施加的应力会在缺陷处形成应力集中,并与阀瓣堆焊层的残余应力叠加,在堆焊层缺陷处萌生裂纹并快速扩展,最终导致阀瓣发生开裂。

A check valve for the high-temperature and high-pressure water system of a certain power plant leaked,and upon inspection,it was found that the valve disc welding layer had cracked.The causes of valve disc cracking were analyzed using methods such as macroscopic observation,chemical composition analysis,metallographic examination,hardness testing,residual stress testing,scanning electron microscopy and energy spectrum analysis.The results show that the chemical composition of the valve disc welding layer was unqualified,and there were defects such as looseness and porosity.When the valve disc was in service,it was subjected to medium impact,and the external stress applied form stress concentration at the defect area,which superimposed with the residual stress of the valve disc welding layer.Cracks initiated and rapidly expanded at the defect area of the welding layer,ultimately led to the cracking of the valve disc.