汽轮机9Cr钢阀座密封面现场堆焊工艺研究与应用

Research and Application of On-Site Surfacing Procedure for Sealing Surface of 9Cr Steel Valve Seat in Steam Turbines

超超临界汽轮机主汽门和再热门阀座的材料均为9Cr钢,密封面上堆焊司太立合金层。很多阀座的堆焊层在高温下长期运行后会出现裂纹。分析了开裂的原因,认为Fe等元素的扩散导致在母材和堆焊层之间形成了脆性相,需要将原堆焊层完全去除后重新堆焊。根据现场堆焊修复的要求,制订了采用自动氩弧焊设备和镍基合金焊材的修复方案。所使用的焊接设备具有自动弧长跟踪、监控摄像、焊枪连续旋转等功能,能够在阀门内部的狭小空间内施焊。在现场将原堆焊层完全去除后采用镍基合金堆焊,并采取焊前预热、层间清理、后热处理等措施保证焊接质量。大量修复实践表明,本套修复工艺能够保证焊接过程的稳定以及较高的工作效率。镍基合金堆焊层的性能能够满足长期运行的要求。

Main steam and reheat main steam valve seats of ultra-supercritical steam turbines are manufactured with 9Cr steel,and the sealing surfaces are welded with Stellite alloy.After long-term operation at high temperature,cracks often appear in the surfacing layers of many valve seats.Based on analysis,it is concluded that the diffusion of elements,Fe for instance,leads to the formation of brittle phases in the steel-Stellite interface,thus the original surfacing layer should be removed completely for re-welding.To meet the requirements of on-site surfacing,a scheme using automatic argon arc welding machine and Ni-based filler metal is proposed.The equipment has functions such as automatic tracing of arc length,monitoring and camera shooting,continuous rotating of welding gun and so on,therefore,it can be used in limited space inside valves.Ni-based alloy filler metal is used in surfacing after thorough replacement of the original surfacing layer,and the welding quality is guaranteed by preheating,inter-pass cleaning and post weld heat treatment.The results of a large number of repair cases show that this welding procedure is reliable and productive,and the Ni-based surfacing layer can meet the requirements of long-term operation.