Page 298 - Pipelines and Risers

Residual Strength of Dented Pipes with Cracks 27 1

affecting pipe fracture strength, since the stress concentration in the bottom of the dent is
proportional to the dent depth.

Figure 15.4 Effect of dent depth to thickness (Ddt).
Parametric study results of dent depth to outside diameter D& is shown in Figure 15.5, from
which it is observed that failure probability increases rapidly when the ratio of D& exceeds a
certain value, say 4%. Care should be taken for the case of large D&.

Figure 15.5 Effect of dent depth to diameter ratio @a).

The effect of crack depth to pipe wall-thickness ratio, dt, on fracture reliability is studied and
shown in Figure 15.6. From which it is observed that the ratio dt is quite influential to
fracture reliability. As the crack depth increase, the reliability decreases rapidly.