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Offshore Platform & FPSO
 
Offshore platforms are structures that require anti-corrosion protection due to their installation in marine environments. The most efficient method of protection against corrosion for offshore platforms is through the use of cathodic protection systems with sacrificial anodes.
Maximum corrosion occurs on a structure at a small distance below the water surface and gradually decreases with depth. Corrosion in the mud part areas is usually much less severe than below the water surface. Both the submerged steel surfaces and the steel in the mud part areas can be cathodically protected.
However, corrosion in the tidal zone or the “splash” zone, which is located above the low water level, may be severe and cannot be fully protected by cathodic protection. In these areas, protection shall be provided by the use of heavy-duty coatings and adequate corrosion allowance by design.
The submerged sections of offshore drilling and production platforms are normally uncoated and rely completely on cathodic protection.
For offshore structures, sacrificial anodes are the standard type of cathodic protection systems. It is preferable to use aluminum-zinc-indium alloy or zinc anodes for cathodic protection, due to their high dependability, immediate availability, and no subsequent maintenance requirements during their design operational life. Anodes are welded onto the structure prior to the installation of the platform. The welding connection serves as both a mechanical and electrical connection.
For offshore structures, the aluminum-indium alloy is mainly used because this combination of materials provides the highest long-term output per unit weight. The design of sacrificial anodes on uncoated structures should take into account the high current required to polarize the steel, and occasional high currents required to repolarize it after heavy storms.
Platforms and Floating Production, Storage and Offloading units (FPSOs) are considered to be special cases as far as cathodic protection is concerned, because their cathodic protection systems are required to have the same operational life expectancy as the intended application (for example 30 years).
Tanks of such structures (platforms, FPSOs) differ in their type of service from tanks on normal trading vessels. The platform and FPSO tanks are used for processing crude oil and may contain large amounts of production water, stationary ballast, or mixtures of (sour) hydrocarbons and water. Also the temperatures of these tanks are typically elevated, and may require a different approach to providing cathodic protection.
For offshore platforms & FPSOs the intervals between dry-docking are much longer than those for ships, thus it is essential for the design life of the sacrificial anode systems to be adequate to cover the full operational period.
 

Anode Type

 

Alternative Installation

 

Specifications

 
Offshore anodes are well known for their large size and heavy weight. They are typically long in length, large in width and thickness. It is common to use seamless pipes as inserts varying in size from ¾” up to 8”. Due to the long design life and high weight of the anodes, the inserts should be thick enough to support the anodes throughout the operational life of the CP system.
Offshore anodes are installed during the construction of the platform. For the installation of the anodes we suggest the use of doubler plates.
Our engineers can recommend the appropriate types of anodes with the suitable type of inserts for each application to minimize the production cost of the anodes and reduce the cost of the cathodic protection system.
SYNCOR anodes are inspected against quality standards that exceed the minimum quality standards from NACE.
Stand Off anode
 
 
 
 
 


Type
LXWXH (mm)
OD (mm)
NW (kg)
ASOE350
1300X101X101
20
35
ASOE800
2360X114X114
25
80
ASOE500
1300X120X120
20
50
ASOE680
1520X133X127
20
68
ASOE1190
1525X184X159
25
119
ASOE1480
2373X160X162
60.3
148
ASOE1750
2500X190X190
114.3
175
ASOE2400
2622X210X10
114.3
240
ASOE3300
2372X252X244
114.3
330
ASOE4350
2910X254X257
114.3
435
ASOE5650
2973X283X283
114.3
565
L=Length , W1=width lower, W2 Width Upper,  H=Height, NW=Net weight, GW=Gross weight 
 
 
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