ABSTRACT
Carbon Steel piping systems experience wall thinning due to the
flow accelerated corrosion phenomenon. A review of the
inspection reports of a typical nuclear pipe indicated that the
predicted minimum wall thickness at the next scheduled outage
may not meet the required minimum acceptable wall thickness
that meets the ASME SEC III NB-3600 criteria for Service
Levels A, B, C & D. This finding triggered a fitness for service
assessment to extend the operating life of this pipe.
This paper summarizes the detailed finite element analysis
performed to re-establish a less conservative MAWT for the tight
radius elbow addressing the catastrophic failure mode under the
primary pressure loading, the plastic instability under bending
moment with coincident pressure loading, and the fatigue crack
initiation under both thermal transients and seismic loadings.
The analysis presented in this paper qualified a uniform wall
thickness profile with 88% of the pressure-based thickness and a
local wall thickness profile with a minimum of 75% of the
pressure-based thickness. These qualified MAWT solutions
significantly extend the component life with a significant
positive economic impact.
SUY Inc. 