核电厂主管道窄间隙焊缝射线检验疑似线性缺陷分析

Investigation of radiographic inspection suspected linear defects in a narrow gap welding of nuclear power plant

为探究核电厂主管道窄间隙焊缝射线检验出现的疑似线性缺陷的产生机理,采用扫描电镜、原子探针等方法分析了存在疑似线性缺陷的焊缝微观组织与显微硬度,讨论了显微组织中的微细孔隙形成原因,并采用孔隙率表征了微细孔隙分布。研究表明,疑似线性缺陷不是真正的焊接缺陷,存在疑似线性缺陷的焊缝组织均由奥氏体与δ铁素体构成,不同区域的δ铁素体含量基本相同,存在疑似线性缺陷的焊缝的孔隙率为0.06%,高于无疑似线性缺陷区域的0.03%。显微组织中微细孔隙率的差异是导致疑似线性缺陷产生的主要原因,但孔隙率的差异不影响焊缝的显微硬度分布。该研究为类似射线检验出现的疑似线性缺陷提供了评判新思路。

In order to investigate mechanism of suspected linear defects indication in radiographic inspection of narrow gap welds in a nuclear power plant,microstructure and micro-hardness of the welds with suspected linear defects were studied by means of scanning electron microscopy and atomic probe.Causes of formation of micro-pores in microstructure were discussed,and distribution of micro-pores was characterized by porosity rate.The results showed that suspected linear defects were not true welding defects.Microstructure of the welds with suspected linear defects was austenite matrix and δ ferrite,and δ ferrite content was the same in different regions.Porosity rate of weld with suspected linear defects was about 0.06%,higher than that of the zone without suspected linear defects,0.03%.Therefore,difference of porosity rate in microstructure was the main reason for suspected linear defects in radiographic inspection,and the difference did not affect microhardness.This study provided a new way to evaluate suspected linear defects in radiographic inspection.