Risk-Based Inspection Technique - Offshore Structures: Design, Construction and Maintenance - page 588

design load. The metocean data were subsequently revised and the design load-
ing became more severe as the years progressed.
As per the discussion in Chapter 7 , in the North Sea, the earlier platforms of
the late 1960s and early 1970s were designed for loading that is 70% of today s

design load. However, in the years between 1980 and 1986, the metocean data
produced design loads that were 45% more severe than the present loads. This
explains the separate tables for the North Sea.
At other locations, the Gulf of Mexico trend is used.
The design loading factor differs from the design practice factor, which
accounts for the level of confidence in the design of structural components
such as joints and members.
Note that the

'

“ year designed ” can generally be taken as 2 years prior to the

year of installation.
The scores for this factor vary from0 to 10 for different ranges of year designed.
Low scores correspond to higher values of design loads and thus low likelihood of
failure, while high scores indicate lower values of design loads and increased like-
lihood of failure. This factor has two tables, one for the North Sea and the other for
elsewhere (combined into one table in Table 8.18 ). However, the scoring principle
is the same for both. The scores vary from 1 to 10 for different ranges of year
designed. The overall weight in the total score is 5.
Where the design is a repeat of a standard design, the year designed should
be taken as the year designed for the first of the standard platforms. Where the
year designed for the first of the standard platforms is not known, a date 2 years

TABLE 8.18 Year of Design

North Sea Year Designed Score

≥ 1972

10

1973 1980 6

1981 1986 1

1987 5

Another Location

Year Designed Score

≥ ≤

1970 10

1971 1974 7

1975 1978 4

1979

1