Page 297 - Pipelines and Risers

270 Chapter 15

Figure 15.2 shows the parameter study of wall-thickness versus safety index and failure
probability. Safety index increases with the increase of pipe wall-thickness, the failure
probability decreases rapidly. But, when the wall-thickness increase to a certain size, the
failure probability doesn’t reduce greatly. This indicates that a minimum wall-thickness can
be defined to achieve a specified target safety level.

t i

Figure 15.2 Effect of pipe wall-thickness t.
The influence of dent depth on fracture reliability is given in Figure 15.3, from which it is
seen that no obvious changes can be observed if the dent depth is not serious. But failure
probability increases dramatically with the increase of dent depth.

Figure 15.3 Effect of dent depth Dd.

Figure 15.4 gives the results of the changes of failure probability and reliability index versus
dent depth to wall-thickness ratio D&. It is interesting to note that this ratio is a key factor