Risk-Based Inspection Technique - Offshore Structures: Design, Construction and Maintenance - page 574

and use brainstorming or other techniques to define the interaction between the
factors and their weight.

Design Practice
Design practice accounts for platform design attributes, such as member sizing,
joints, pile design and others. The intent is to quantify the inherent strength in a
platform depending upon the point in time in which it was designed. The year it
was designed was selected because it is most reflective of the strength of the
platform. The year of design should be different from the date of installation;
in some cases, the platform may have been designed several years prior to
being installed.
The indicated dates generally match up with the continued development of the
API RP2A recommended practice for design of offshore platforms in U.S. waters.
The first version of API RP2A, issued in 1969, was the first good guideline for plat-
form design. The year 1970 is used here (conservatively) to reflect the fact that,
although the first edition was issued in 1969, the document did not reflect common
practice until about a year later. The next major update to RP2A was the inclusion
of joint design practices, in approximately 1975. In 1979, API RP2A was updated
to the point that the API Section 17 Committee on assessment of existing platforms
deemed that the guideline had reached maturity and that platforms designed to the
guideline since that time are of good quality.
Table 8.4 presents an example for a score between 0 and 10 for the year of
design of the platform, a factor that estimates the level of confidence that can be
placed on it due to the state of design practices prevalent at that time. A plat-
form designed later than 1979 scores 0, to indicate that the platform is reliable
due to the good and improved design practices. Platforms designed before 1970
score 10 because they tend to have the highest probabilities of failure. Note that
the overall weight of the total score is 5.

TABLE 8.4 Design Practice Factor

Year of Design Score

≥ 1970

10

1971 1974 7

1975 1979 4

1979 0

Unknown 9