Fatigue fracture and probabilistic assessments of a cone and pipe welded
structure of stainless steels
Abstract
Using thin-walled cone-pipe welded joints of stainless steels, fatigue
tests under bending loads were carried out. The test data were
statistically analyzed with the Benard’s approximation, Gaussian,
2P-Weibull, and 3P-Weibull distributions. Stress–life curves at
different failure probabilities by a constant strength scatter band
model were obtained. The metallographic structures were investigated,
and the stress concentration states were analyzed to elucidate the
causes of the strengths and scatters. In the high-cycle fatigue regime,
the 2P-Weibull distribution was mostly in agreement with the Benard’s
approximation, and the coefficient of determination was 0.9666. The
microstructure of the weld metal with a high weld opening angle was
mainly ferrite phase with 20% austenite distribution. The crack
initiation point was close to the weld interface, but the propagation
direction was at a right angle, and initially penetrated the heat
affected zone of the cone, leading to the high fatigue strength. The
stress concentration factors depended on the weld opening angles,
indicating the main factor which affected strengths and scatters.