超超临界锅炉末级过热器异种钢接头机械性能分析

Mechanical Performance Analysis of Dissimilar Steel Joints for the Final Superheater of Ultra-Supercritical Boilers

在常规割管检验中发现,某超超临界火电机组锅炉末级过热器异种钢接头(SA-213T92/SA-213TP310HCbN)处存在两处加工坡口,因接头尺寸存在差异,焊接前对管道内壁坡口进行加工处理,但未消除坡口的倒角及加工残留缺陷。对该接头进行了宏观检查、强度校核计算、金相组织分析、力学性能检测及能谱分析,根据试验结果可知:该末级过热器接头内壁处的加工坡口削弱了接头处塑韧性能,该处加工坡口加大了该位置的应力集中程度,使得试样在拉伸颈缩阶段局部区域发生严重的塑性变形,导致接头在该处变截面应力集中区发生断裂,延伸率严重低于标准要求。而车削加工的表面残留缺陷及车削加工形成的残余应力场进一步削弱了接头的机械性能,加快了在拉伸颈缩阶段试样微裂纹生成及扩展的速率,直至其最终断裂。

In the conventional pipe cutting inspection,it was found that there were two processing grooves at the dissimilar steel joints(SA-213 T92/SA-213 TP310 HCbN)of the final superheater of the boiler of a certain ultrasupercritical thermal power unit.Due to the difference in joint size,the groove on the inner wall of the pipeline was processed before welding,but the chamfering of the groove and the residual defects of processing were not eliminated.Macro inspection,strength check calculation,metallographic structure analysis,mechanical performance testing and energy spectrum analysis were carried out on the joint.According to the test results,the processing groove on the inner wall of the final superheater joint weakened the plastic toughness of the joint.The processing groove increased the stress concentration at this position,which leaded to severe plastic deformation in the local area of the specimen in the tensile necking stage,resulting in the fracture of the joint in the stress concentration area of the variable section,and the elongation was seriously lower than the standard requirements.The residual defects on the surface of the turning process and the residual stress field formed by the turning process further weakened the mechanical properties of the joint,and accelerated the generation and growth rate of micro-cracks in the tensile necking stage of the sample,until the final fracture.