Fatigue Reliability Assessment of Pipeline Weldments Subject to Minimal Detectable Flaws

The study presents a probabilistic modeling of the fatigue crack growth prediction of the pipeline steel weldments in nuclear power plants in the context of an integrated structural health monitoring setting. Fatigue testing of the crack growth in the fusion line region of the steel weldments is made using compact-tension specimens. In particular, the uncertainty of the crack growth due to different crack plane orientations is investigated in details. A total of six orientations of the specimens are manufactured and tested according to the ASTM standards to obtain the fatigue crack growth data. The Bayesian method is used to identify the probability density function of the parameters of the Paris’ fatigue crack growth model. Using the concept of damage tolerance, the reliability model of the pipeline weldments given the minimal detectable internal flaws of the ultrasonic nondestructive evaluations can be established. The time-dependent reliability of the pipeline weldments is obtained using the efficient first-order reliability method. Results indicate the uncertainty of the orientations of the flaws plays an important role in the overall reliability of the pipeline weldments.