长距离输油泵扩流器焊缝失效机理研究

Study on Weld Failure Mechanism of Diffuser for Long Distance Oil Delivery Pump

离心泵作为管道运输的重要工具,其安全性和使用寿命会极大制约管道运输成本。离心泵由内部转子和外部扩流器组成。其中,外部扩流器由钢板焊接而成,钢板间的焊缝作为扩流器的薄弱环节,是离心泵的一个主要失效部位。因此,以某输油站已失效扩流器为原材料,针对扩流器焊缝进行扫描电镜(SEM)、能谱(EDS)和电子背散射衍射(EBSD)检测,结合3种检测结果和扩流器工作环境,从微观结构角度分析扩流器焊缝的失效机理;根据EBSD检测结果计算焊缝、热影响区及基体的临界位错密度ρ^(GND),定量比较3个位置的强度和韧性。结果表明:热影响区强度和韧性最高,基体次之,焊缝最低;夹渣、划痕和残余奥氏体等缺陷为焊缝腐蚀、开裂创造了初始条件;微裂纹在循环应力和腐蚀介质共同作用下迅速扩展,最终导致扩流器焊缝失效。本研究的成果可以为离心泵的使用和制造提供一定参考。

Centrifugal pump is an important tool for pipeline transportation,and its safety and service life will greatly restrict the cost of pipe-line transportation.The centrifugal pump is composed of internal rotor and external diffuser,among which,the external diffuser is welded from steel plates,the weld between the steel plates as the weak link of the diffuser,is a main failure part of the centrifugal pump.Therefore,in this paper,a failed diffuser of an oil transmission station was used as the raw material,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and electron back scatter diffraction(EBSD)detection for the welds of the diffuser were conducted,and the failure mechanism of the welds of the diffuser was analyzed from the perspective of microstructure,combining the three detection results and the work-ing environment of the diffuser.Based on EBSD test results,the critical dislocation densityρ^(GND) of weld,heat affected zone and substrate was calculated and the strength and toughness of the three positions were quantitatively compared.Results showed that the heat affected zone had the highest strength and toughness,followed by the substrate,and the weld was the lowest.Defects such as slag inclusion,scratch and residual austenite created the initial condition for weld corrosion and cracking.Micro cracks rapidly expanded under the combined action of cyclic stress and corrosive medium,and eventually leading to weld failure of diffuser.The results of this study could provide some reference for the use and manufacture of centrifugal pumps.