Deepwater RetroLink Low-Cost Cathodic Protection System for Smaller Offshore Structures

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RetroLink™
Low-Cost Cathodic Protection System
for Smaller Offshore Structures
by Deepwater Corrosion Services

Low-cost anode array for cathodic protection consisting
of a series of anodes cast onto a wire rope core.

A RetroLink cathodic protection array consists of anodes cast onto
a wire rope core for current conduction and support.

Product Overview RetroLink by Deepwater is an anode array that comprises a series of anodes cast onto a wire rope core. The anodes have been sized and spaced to provide low-cost, reliable cathodic protection for a wide variety of offshore, inshore or marine structures. Installation expenditures are minimal. In most cases, a diver is not required. RetroLink strings come in three standard sizes of 30 ft, 60ft and 90 ft. These may be deployed in three basic ways: Surface suspended with trailing mud anodes. Used for 3-5 year CP of offshore structures in 90 fsw or less. Used as riser or infield pipeline CP system with insulated hang-off option. Subsea suspended with trailing mud anodes. Used to supplement RetroPod on 10-year systems. Mud deployed. Used to protect ultra-shallow water structures, such as offshore wind turbine caissons. Used as retrofit system for offshore pipelines. The wire rope core provides both the electrical conductivity through the anode system and superior mechanical support. The strings are made with up to fifteen anode segments. These may be cut to length and deployed in many ways to provide cathodic protection just where it is needed. If laid in the mud, the system life can be extended to almost 10 years. RetroLinks should always be installed such that at least two anodes trail on the bottom. In this configuration, sea movements are attenuated, and the string will not wrap around the structure. Select zinc or aluminum anode material depending on the salinity of your water. Zinc anodes are recommended if water is less that 12% full strength seawater (4.2 ppt Cl). Aluminum anodes are recommended for all other applications.
		RetroLink caisson installation.

		RetroLink ready to ship.

		RetroLink installation.

RetroLink Sizing

	RetroLink 30 ft			RetroLink 60 ft			RetroLink 90 ft
Total number of anodes		5	5		10	10		15	15
Number of anodes in water		3	1		8	1		13	1
Number of anodes in mud		2	5		2	9		2	14
Current output, amperes *		4.4	1.9		9.9	5.5		14.9	5.3
Life at current output, years		3.5	11		4.1	12		4.5	13
Bare steel protected area, m²		88	38		198	72		298	106

* Figures given assume the following typical values: seawater resistivity 25 ohm-cm, mud resistivity 75 ohm-cm, cathode potential -0.800V vs Ag/AgCl, current density 50 mA/m².

System Components

RetroLink Strings: Shallow 30 ft, 5 anodes; intermediate 60 ft, 10 anodes; deepwater 90 ft, 15 anodes.
Leader Assembly: Standard 25 ft length (can be field adjusted). Coated wire rope with all hardware for either surface suspension with Topside Suspension Bracket, or subsea attachment with RetroClamp.
Topside Suspension Bracket: Allows topside suspension of RetroString may be electrically isolating for riser retrofits.
RetroClamp: Used for subsea attachment and electrical grounding to either jacket tubular or subsea pipeline.
V-String / SunStation: Integral monitoring system available for special applications.
Design Guide: Prints out a cathodic protection solution and a material list that can be priced with a simple e-mail or phone call to Farwest.

RetroLink installation.

Installation

A leader assembly is used for above-water suspensions and uses PVC-coated wire rope for corrosion resistance. The modular design allows the hang elevations to be easily adjusted in the field. The weld-on topside suspension assembly can be attached to horizontal or vertical members. The isolator can be used to have Links protect offshore risers. Links can be attached subsea using a modified hang-off. This allows the links to to provide large currents cost effectively to deeper water structures when a limited design life is adequate.

Applications

1. Minimal Offshore Structures

Many offshore structures that sit in less than 85 f.s.w can have the corrosion protection system replaced very cost effectively using RetroLink. The system can be quickly installed with a small topside crew. No diving is required. The system can provide 5 to 7 years of protection.

2. Offshore Wind Turbines

Foundation piles may be placed up to 1 year before the transition structure is installed. During this period RetroLinks can save the day, then can be recovered and redeployed during periods of grid power interruption. For quick, painless retrofit, this is the ideal system.

3. Docks, Harbors and Wharves

RetroLink systems are reliable and easy to maintain using small under-dock access vessels and equipment commonly found around such installations. A simple design guide enables the facility owner to apply adequate levels of cathodic protection following a simple field verification procedure. Links have been installed to provide cathodic protection to bridge pilings, whether reinforced concrete or steel. The installation is quick and easy.

4. Temporary Protection

Vessels in long-term wet storage can be protected cost-effectively by this system. Simple owner verification that submerged parts of the vessel are not corroding is possible with the optional inspection kit.

5. Pipeline Risers

Short infield lines can be effectively retrofitted with RetroLinks, using the host structure as the support and grounding to the pipeline side of the insulating flange.