Reliability Improvement Method of Weld Zone in Water Wall Tube for an Ultra Supercritical Coal Fired Boiler

초초임계압 석탄화력 보일러 수냉벽 수관의 용접신뢰성 향상방안

This paper presents failure analysis on weld-joint of the waterwall tubes in USC boilers. Visual inspections were performed to find out the characteristics of the fracture. Additionally both microscopic characteristics and hardness test were carried out on failed tube samples. Failures seem to happen mainly because the welding process such as preheating and PWHT(post-weld heat treatment) was not conducted strictly. Thus, this paper has the purpose to describe the main cause of the poor welding process and to explain how to prevent similar failures in those weld-joints.