Abstract
The unified creep constraint parameter Ac and fracture parameter C∗ for axial semi-elliptical surface cracks with high aspect ratio in pressurized pipes have been investigated by three-dimensional finite element analyses. The results show that the constraint level near surface part is lower than that at the deeper part of crack front. With increasing crack aspect ratio a/c and decreasing crack depth a/t, the constraint levels decrease. The parameter Ac solution for high aspect ratio cracks has been obtained. The crack aspect ratio a/c has significant effect on the C∗ distributions along the crack fronts. For high aspect ratio cracks, the maximum C∗ along the crack fronts occurs near surface part. With increasing crack aspect ratio a/c from 0.2 to 2, the creep crack initiation location will change from the deepest part of the crack front to the near surface part. For high aspect ratio cracks, if the calculations of C∗ and Ac at the deepest point is used to predict creep crack initiation life, non-conservative results may be produced. More benefits from incorporating constraint effects may be obtained for creep life assessments of pipes with high aspect ratio cracks due to their lower constraint.
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