Risk-Based Inspection Technique - Offshore Structures: Design, Construction and Maintenance - page 566

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failure Consequence). The likelihood of failure is defined as the probability of

failure or the failure rate.
The consequence of failure is the combination of losses that could be
incurred as a result of a failure.
Classification factors that do not require any analytical assessment are pre-
sented that enable the likelihoods and consequences of failure to be quantita-
tively evaluated or qualitatively categorized.
The likelihood of structural collapse is a function of two primary factors, the
platform strength or capacity, and the extreme loads that affect the offshore
structure. The likelihood categorization system identifies the platform character-
istics or factors that affect the platform strength and loads. For example, factors
that decrease the strength of the platform and its capacity to carry the applied
load will increase the likelihood of platform failure. Factors that contribute to
increasing the applied load on the platform or the offshore structure in general
will also increase the probability of failure.
The overall consequence of failure is the sum of three main components:
environmental losses, business losses and injury/safety-related losses. The
effect of each of the three consequences is converted to a dollar value (in
USD) and the effects are summed to give the overall consequence. While the
resulting dollar value does not represent the total amount of money that
could be lost due to a failure, the monetary concept allows the three components
to be combined.
After each platform is categorized in terms of likelihood and consequence of
failure, the categories are entered into the risk matrix to establish the overall
relative risk ranking. Note that the risk matrix can be a 4x4 or 5x5 matrix.
The relative risk rankings are high (red), moderate (yellow), low (green) and
insignificant (white).
In parallel with the risk assessment, the platforms have also been grouped into

“ that represent platforms with similar configurations and similar duties.

Hence, in addition to identifying and ranking the high-risk platforms across the
overall fleet of offshore structures, high-risk platforms can also be identified within
each family. The two rankings make possible rational decisions about where to
focus and how to distribute the resources of the rehabilitation project.

families ”

8.3.1 Likelihood (Probability) Factors
This section presents the factors that influence the likelihood of jacket structural
failure (the likelihood is equal to the probability of failure in quantitative risk
assessment). The factors fall into two groups, those that relate to the strength
of the platform, listed in Table 8.1 , and those that relate to the loads applied
to the platform, listed in Table 8.2 .
The factors should be defined separately for different locations, based on the
expertise of the owner companies and regional data about the factors that can
affect the structures. In addition, as more detailed inspections are undertaken,