Risk-Based Inspection Technique - Offshore Structures: Design, Construction and Maintenance - page 570

the number of factors can be increased. The values in Table 8.2 are just guide-
lines to illustrate this approach. The condition of operation, environment, the
back history and the data you have collected should all be examined. For exam-
ple, if for a certain structure, no member thicknesses have been measured to
check for corrosion, member thickness is not included. However, once thick-
ness measurements become available, this factor should be introduced. Exam-
ples of factors are:
Strength factors:

Design practice

●

Number of legs and bracing type

●

Foundation

●

Risers and conductors ●

Boat landings ●

Grouted pile

●

Damaged, missing and cut members

●

Splash zone

●

Flooded members ●

Cathodic protection survey and anode depletion ●

Inspection history

●

Remaining wall thickness

●

Load factors:

Design loading ●

Marine growth

●

Scour

●

Topside weight change

●

Additional risers, conductors and caissons

●

Wave-in deck

●

Earthquake load.

●

Interactions
Most of the above factors are not truly independent. Some of the factors have
strong interactions. For example, the bracing type and the number of legs affect
how much a damaged member decreases the strength of the platform and how
much it increases the likelihood of failure.
According to De Franco et al. (1999) , the complex interactions between dif-
ferent platform characteristics might make it impossible to develop a risk-based
inspection system that doesn t depend on a great deal of structural details. The

team evaluated the interaction of each pair of factors, and the resulting relations
between the likelihood factors and their interactions are presented in the matrix
in Table 8.3 . The H, M and L mean high, moderate and low interactions,
respectively.

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