某660MW超超临界机组热段疏水管道接管座的开裂原因

某火电厂660 MW超超临界机组投运不久,其热段疏水管道接管座开裂,导致蒸汽泄漏。对该接管座进行了化学成分、硬度和显微组织分析,并根据管道实际布置情况建立三维实体模型,采用热固耦合有限元方法对该结构受力进行仿真分析。结果表明:该接座管化学成分、硬度、显微组织满足要求,有限元仿真得到最大应力位于接管座与主管连接焊缝下边缘,与实际开裂位置一致;其开裂是由于疏水管吸收变形能力有限,且管道布置不合理造成管道热膨胀受阻,使得接管座区域产生较高拉应力而导致的。通过加设U形膨胀弯的方式增强管道柔性,降低结构应力水平后,疏水管道接座管运行约1 a未发生开裂。

Reasons for Cracking of Nozzle Socket of Hot Section Drain Pipe of a 660 MW Ultra-supercritical Unit

After short operation of the 660 MW ultra-supercritical unit of a thermal power plant,the nozzle socket of the drain pipe cracked in the hot section,causing steam leakage.The chemical composition,hardness and microstructure of the nozzle socket were analyzed.A three-dimensional solid model was established according to the actual layout of the pipe,and the force of the structure was simulated and analyzed by the thermo-solid coupling finite element method.The results show that the chemical composition,hardness,and microstructure of the nozzle socket met the requirements.The maximum stress obtained by the finite element simulation was located at the lower edge of the connection weld between the nozzle socket and the main pipe,which was consistent with the actual cracking position.The cracking was due to the limited ability of the drain pipe to absorb deformation,and the higher tensile stresses in the nozzle socket area induced by the blocked thermal expansion of the pipe because of the unreasonable pipe layout.After adding a U-shaped expansion bend to enhance the flexibility of the pipe and reduce the structural stress,the nozzle socket of the drain pipe did not crack during operation for about 1 a.