Cause Analysis on Cracking of Welded Joint of Tee in a Power Plant

Several crackings occurred at the weld joint between the main steam pipe tee and the upper connecting pipe in a power plant. The causes of cracking of the welded joints were analyzed by means of non-destructive testing, hardness testing, metallographic examination, pipe system stress calculation analysis, pipe system thrust calculation analysis, finite element analysis and so on. The results show that the pipe system arrangement near the tee of the pipe was unreasonable. The bending stress at the welded joint was large and there was stress concentration. The maximum stress exceeded the high temperature endurance strength of the welded joint. In addition, the aging of the microstructure at the crack site decreased the mechanical properties of the welded joint, which led to the creep cracking of the welded joint.