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Figure 9.10 A fatigue of weldments master curve was statistically fit to over one thousand test results ( Reproduced courtesy: M. Prager, The Master S-N Curve Method, WRC Bulletin 523, 2010)

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Eq. SS range, MPa

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Upper99 Upper95 S-N data

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1. E+02

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1. E+06 1.E+07 1.E+08

Cycles to Failure

9.5.2 Residual stress estimates for fitness for service (FFS) In performing FFS or ECA fracture mechanics based defect assessment of a welded component, a through- wall residual stress distribution is required. A major concern is that drastically different residual stress distributions are given for the same joint configuration and welding conditions by various Codes and recommended procedures. Recent work has shown that although residual stresses may depend upon a large number of variables including joint geometry, material composition and welding process parameters, some of the distribution of residual stresses can be estimatedwith only a few important parameters for engineering assessment purpose. These governing parameters need to be better understood however in terms of their contributions to a through-wall residual stress profile. With that knowledge, functional relationships can be constructed to describe a broad spectrum of the residual stress distributions. Specifically, the underlying mechanics basis on which the residual stress profiles are being developed requires further study, Parametric functional forms for residual stress distribution characteristics over a wide range of geometries and welding conditions need to be explored ( Figure 9.11 ).

Figure 9.11 Residual stress patterns were discerned after numerous FEA studies involving a broad range of welding variables ( Reproduced courtesy: M. Prager, Recommendations for Determining Residual Stresses in Fitness-for- service Assessment, WRC Bulletin 476, 2002)

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