In order to achieve a better understanding of residual stress distribution characteristics associated with nozzle welds, this paper focuses on the identification of key parameters that contribute to the development of through-thickness membrane and bending components. This is because, as demonstrated in recent publications by the same authors (Song and Dong, 2016–2017), statically equivalent membrane and bending content in a given residual stress distribution play a far more critical role in fracture driving force calculation in Fitness-for-Service (FFS) assessment. To do so, a recent detailed investigation to residual stress distributions in nozzle welds is presented in this paper, covering nozzle radius to wall thickness ratio from 2 to 50, heat input from 400 J/mm to 1000 J/mm, weld joint types including set-in nozzle weld and set-on nozzle weld. By means of a residual stress decomposition technique, controlling parameters that govern through-thickness membrane and bending stresses have been identified, which are nozzle radius to wall thickness ratio (r/t) and linear heat input parameter (Q). Then, a unified functional form for representing through-thickness residual stress profile in nozzle weld is presented for supporting fitness for service assessment, e.g., by means of API 579-RP.

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