Civil Engineering Reference
In-Depth Information
point is below the water sea level, the seawater-exposed section above this point
is also included. A current drain for 30 m of chain is also included for CP of
anchoring arrangements using chains.
6.4.7 Design Calculation for CP System
In design of a CP system for a fixed offshore platform, detailed design is nor-
mally preceded by conceptual design activity in the front end engineering
phase. During the conceptual design phase, the type of anodes and fastening
devices are selected, taking into account forces exerted on anodes during instal-
lation and operation. Moreover, any coating systems to be applied to specific
areas or components should also be specified, as this is the main factor in cal-
culating current demands for the CP system and also in calculating the required
total net mass of anode material.
If no CP conceptual report has been prepared, then the basic concepts
for detailed CP design are defined by the purchaser in some other reference
document(s) to be included in an inquiry for CP detailed design.
The checklist of information and any optional requirements provided by the
purchaser includes:
conceptual CP system design report
●
design life of CP system to be installed
●
the project design basis, which are salinity and temperature as a function of
depth for calculation of anode resistance, water depth and the level of seabed
for platform substructures
●
environmental and installation parameters affecting forces exerted on
anodes
●
structural drawings and information on coating systems as required for calcu-
lation, including components that may exert temporary or permanent current
drain
●
identification of any interfaces to electrically connected component systems
with self-sufficient CP systems, such as pipelines and other connected facilities
●
any specific requirement for CP design parameters to be applied, such as
coating breakdown factors and current drain to wells
●
any specific requirements for anode material and anode design
●
The purchaser ensures that valid revisions of drawings and specifications
affecting calculation of current demand for CP and location of anodes are avail-
able to the contractor during the design work. All necessary information is pro-
vided to the contractor for calculation of the overall current demand (e.g.,
conductors for production platform substructures and production control system
for subsea valve trees).
In the design of CP systems for the structure jacket, it is advisable to divide
the areas into separate surface areas to be protected. The division into areas may
be based on depth zones.
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