Heat recovery steam generator (HRSG) superheater outlet headers are exposed to cyclic stresses under varying transient operating conditions. Three different tube to header connections are analyzed. Cold, warm, and hot startup cycles are defined along with a load change cycle. These cycles are used to develop boundary conditions for a transient three dimensional finite element analysis of each detail. The results show that the highest stresses are away from the tube to header weld area. For the startup cycles analyzed, equations are presented for cycle life determination.