by Phillip E. Prueter, P.E. / Jul 14, 2013

Current minimum spacing requirements for local thin areas near structural discontinuities in pressurized components are outlined in Part 5 of API 579-1/ASME FFS-1, Fitness-For-Service. For Level 1 and Level 2 assessments, it is recognized that the current spacing criteria can be overly conservative. This paper examines preliminary results from a Materials Properties Council Fitness-For-Service Joint Industry Project that is intended to evaluate the current spacing criteria and develop a potential methodology for new assessment procedures based on computational results. Finite element models are employed to examine the interaction of stresses between local thin areas and stiffening rings and to investigate the relationship between local thin area spacing and pressure capacity. Performance is compared for models with and without areas of local metal loss near stiffening rings to form a potential basis for an improved assessment procedure. Furthermore, a criterion for classifying stiffening rings as major axisymmetric structural discontinuities is proposed.

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