This paper discusses a fitness-for-service (FFS) evaluation of a hot reheat (HRH) piping system with about 400,000 hours of operation. It discusses significant differences between the as-designed and simulation as-found piping stress analyses. The significant range of stresses in the piping system illustrates that the few lead-the-fleet girth welds should have significant creep damage decades before many other girth welds.
Since the weldment examination intervals will correspond to scheduled outages, the creep life uncertainties can be grouped into high, medium, and low priorities (e.g., 0–10 years, 10–20 years, and beyond 20 years) with high confidence of rankings among the selected groups.
There are 14 girth welds in this HRH piping system. In this case study, only 2 girth welds were evaluated as high priority nondestructive examination (NDE) locations and 1 girth weld was evaluated as a medium priority location for the next set of NDE reexaminations. Many of the low priority girth welds have predicted creep rupture lives substantially beyond 1,000,000 operating hours.