Civil Engineering Reference
In-Depth Information
prior to the year of installation may be taken, although this may not be
conservative.
It is evident from
Table 8.18
that the year designed parameter interacts with
location to distinguish the North Sea from the rest. The scores are based on the
design hydrodynamic loading adopted from the metocean data as per practice in
the year of design.
Marine Growth
Marine growth is a very simple factor but can cause many problems, as
discussed in
Chapter 3
. The wave force that affects the load on the structure
is a function of member diameter, so marine growth will increase member
diameter and increase the wave force correspondingly. This factor uses actual
measured marine growth (mm)/design marine growth (mm).
Table 8.19
illustrates scores for this factor between 0 and 10, where a higher
score signifies greater risk. If the measured marine growth exceeds the design
value, it increases the environmental load on the platform and therefore
increases the likelihood of failure for the platform. The table allots a score of
10 to platforms whose measured marine growth exceeds the design value by
50% or more.
If there are no data available, the score may be reduced to 5 if underwater
surveys indicate that the levels of marine growth are low, that is
50 mm thick.
This parameter does not have any interdependence with other factors or
parameters in the likelihood category. The measured marine growth is an
inspection item. It is divided by the design marine growth (design data sheet)
to obtain the ratio in terms of percentage.
Although marine growth is an inspection-related input, the parameter that
causes failure is the environmental loading. Excessive marine growth, espe-
cially when it far exceeds the design growth, results in higher loading on the
platform than it was originally designed for.
<
TABLE 8.19
Marine Growth Factor
Measured/Allowable Marine Growth in Design
Score
>
90%
0
90%
135%
3
135%
150%
8
150%
10
No data
10
Search WWH ::
Custom Search