Risk-Based Inspection Technique - Offshore Structures: Design, Construction and Maintenance - page 594

TABLE 8.24 Likelihood Category

Category Range

1 ≤ S1

2 S1 - S2

3 S2 - S3

4 S3 - S4

5 > S4

120

95%

100

70%

80

60

50%

40

5%

20

0

S1 S2 S3 S4

260 280 300 320 340

Likelihood score

360 380 400 420 440 460

FIGURE 8.2 Cumulative density function (CDF) for likelihood score strength.

cumulative density function can be obtained, as shown in Figure 8.2 . Because
the category limits identify the best and worst 5% of the platforms, it is
assumed that 5% of the platforms have a high likelihood of failure and 5%
of the platforms have an insignificant likelihood of failure. The intermediate
category limits are intended to represent the 50th and 70th percentiles. This
distribution of the category limits assigns two category ranges for platforms
that have better-than-average likelihood scores and three ranges for platforms
that have worse-than-average scores. Consequently, it will be necessary to
review and modify the ranges once data from the jacket evaluation and scor-
ing become available, to ensure that the intent is being realized. The values of
the categories S1, S2, S3 and S4 will be obtained from the cumulative density
function (CDF).