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10 000
1000
100
10
1.
E+02
Eq. SS range, MPa
Cycles to Failure
Mean
Lower99
Lower95
Upper99
Upper95
S-N data
1.
E+03 1.E+04
1.
E+05
1.
E+06 1.E+07 1.E+08
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)
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)
