In Service Defects For Both Steel And Concrete Flashcards
Inter-tidal and splash zones
Corrosion is more aggressive in this area and must be more carefully
monitored.
Marine growth build-up is greater in the top 20m of the sea and is
particularly dense in the inter-tidal region. This will increase mass and drag
in a part of the structure most vulnerable to these effects. Marine growth
may also affect corrosion rates.
The risk of physical damage is greater in this region due to the risk from
floating objects and, in those parts of the world that are susceptible,
icebergs may collide with the structures. Certainly this is possible in offshore
Canada for example.
Risers
Are components common to both types of structures, although on concrete platforms they may be installed inside the shaft
Conductors and conductor guide frames
As with risers, these components can be common to all platforms and they are
exposed to the same risk of failure as risers, perhaps more so as there are greater vibrations possible with these components than the rest of the platform.
Furthermore, conductors are normally kept in place by guides rather than clamps, which allow relative movement between the conductor and its guides; hence wear must be monitored, as there is a real possibility for fatigue cracking
to occur.
Caissons
Caissons are another group of components carefully monitored on an annual basis. There is a common problem with this component when it is used as a pump caisson. The pump is commonly suspended from the surface inside the caisson. It is common for the pump to be at about 18m water depth level inside
the caisson. Conditions at this point on the inside of the caisson are near perfect for corrosion to progress at excessive rates. This has caused component
failure on more than one occasion
Overloading
Changes in the working practices and other commercial factors may lead to extra items of equipment being installed, such as a newer, bigger crane. This may lead to overloading if not carefully monitored.
