This case study focuses on the analysis and repair of a riser pipe in a waste heat boiler system. The initial damage resulted from inadequate tapering at the welded joint, causing high stress concentration and fatigue cracks. The first repair involved cutting and replacing the damaged section, performing proper taper transitions, and applying preheating and post-weld heat treatment. However, thermal stress during the repair process led to a bulge near the repaired joint. To prevent recurring failures, two repair solutions were proposed. Solution 2, which involved simultaneous preheating for all pipes, was successfully implemented. This case study highlights the importance of proper tapering practices and considering thermal expansion in equipment repairs.