Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 525

7.12.2 Load Reduction
Marine Growth Removal
Marine growth accumulates on the legs and bracing with time. As a result, the
diameter of the members affected by waves will increase, so the lateral load due
to waves will increase as well with time and can become critical if the marine
growth thickness increases more than the predicted marine growth thickness in
design. Therefore, removing marine growth can enhance structural capacity.
Removal of marine growth can be performed by different techniques. A new
technique for marine growth removal uses a mechanism that is fixed on the
leg and bracing, as shown in Figure 7.31 .
This technique generates substantial savings in cleaning and prevention
costs (up to 80% reduction) for existing structures, reduces fabrication and
installation costs for new structures and offers both removal and prevention cap-
abilities. The mechanism can be easily installed by riggers or abseilers from
above the water surface and by divers or ROV underwater. It enables instant
visual inspection of the substructure without prior cleaning and it is harmless
to the environment. It is effective in reducing the weight of marine growth
for decommissioning of structures and eliminates safety hazards encountered
by divers using high-pressure water jetting, which is the traditional method,
especially in the splash zone environment.
The fouling system is a painting technique that prevents the accumulation of
marine growth on the members and maintains existing structures free of
regrowth after cleaning of previous growth.
FIGURE 7.31 Working mechanism for marine growth removal.