Protecting the structures that support offshore production
Offshore jackets spend their entire service life submerged in seawater. Jacket anodes are attached to the structure's members and corrode in place of the steel, supplying the protective current that keeps the platform sound for its full design life.
Every jacket is different, so we treat each anode set as an engineered product. Alloy, net weight, shape, insert design and quantity follow the project's CP calculation and structural drawings.
RELI ANODES draws on the Reliable Group's industrial experience since 1975 across oil and gas, petrochemical, power and infrastructure — combining materials knowledge with pipeline and corrosion-protection engineering.
Jacket anode configurations
The configuration is chosen to suit the member size, location on the structure and installation method.
Stand-off anodes
Cast on steel inserts that hold the anode clear of the member. This maximises current output and is the most common arrangement on jacket structures.
Flush-mounted anodes
Mounted close to the steel surface where space, drag or handling during installation is a concern.
Retrofit anodes
Designed for life extension or additional protection of existing platforms, with mounting arranged to suit the installed structure.
Key features
Built for seawater
Designed for continuous immersion on submerged offshore steel.
Engineered design
Configuration and dimensions developed from your CP design and drawings.
Alloy choice
Aluminium or zinc alloy, selected for the application and specification.
Full design life
Net weight and quantity sized for the required protection period.
Technical data
Typical supply parameters. Final values are confirmed against your approved drawing and CP design.
- Product
- Jacket / offshore structure anode
- Protection method
- Sacrificial cathodic protection
- Typical applications
- Offshore jackets, platforms and submerged steel structures
- Service environment
- Seawater and marine
- Materials
- Aluminium alloy and zinc alloy
- Configuration
- Project- and structure-specific
- Dimensions
- As per engineering requirement
- Installation
- Welded / project-specific
- Design life
- As defined by the CP design
Materials and standards
Choose the alloy to suit the environment and CP design, then the chemistry to suit your specification.
Aluminium (Al-Zn-In)
The usual first choice offshore: 2,550–2,750 Ah/kg and low weight for long design lives.
- Galvalum III equivalent
- DNV / ISO
- Alanode
Zinc
Compact, self-regulating and well proven — often chosen for hulls and confined spaces.
- MIL-DTL-18001
- ASTM B418 Type II
Available grades
Galvalum III equivalent
A well-established Al-Zn-In chemistry for seawater service, cast to equivalent composition limits.
DNV / ISO
Al-Zn-In composition in line with the limits given in DNV-RP-B401 and ISO 15589-2.
Alanode
Aluminium alloy chemistry supplied to the applicable Alanode composition limits.
US Military spec. (MIL-DTL-18001)
Zinc alloy with controlled aluminium and cadmium additions, widely specified for seawater service.
ASTM B418 Type II
High-purity zinc with very tight iron limits, typically specified for soil and fresh-water service.
Client specification
Your own chemistry, testing and documentation requirements, reviewed and confirmed with you before production starts.
Chemical composition
Composition limits in % by weight for the chemistries we supply.
Aluminium alloys
| Element | Galvalum III (equiv.) | DNV / ISO | Alanode |
|---|---|---|---|
| Zn | 2.0 – 6.5 | 2.5 – 5.75 | 0.50 – 5.00 |
| In | 0.01 – 0.02 | 0.016 – 0.04 | 0.005 – 0.05 |
| Si | 0.08 – 0.20 | 0.12 max. | 0.10 max. |
| Fe | 0.12 max. | 0.09 max. | 0.13 max. |
| Cu | 0.006 max. | 0.003 max. | 0.01 max. |
| Cd | 0.002 max. | — | — |
| Others (each) | 0.02 max. | 0.02 max. | 0.02 max. |
| Others (total) | 0.06 max. | — | — |
| Al | Remainder | Remainder | Remainder |
Zinc alloys
| Element | US Military spec. (MIL-DTL-18001) | ASTM B418 Type II |
|---|---|---|
| Al | 0.10 – 0.50 | 0.005 max. |
| Si | 0.125 max. | — |
| Cd | 0.025 – 0.15 | 0.03 max. |
| Fe | 0.005 max. | 0.0014 max. |
| Pb | 0.006 max. | 0.003 max. |
| Cu | 0.005 max. | 0.002 max. |
| Zn | Remainder | Remainder |
Specification note
Final chemistry should always be confirmed against the applicable material specification and approved project documents before production.
Electrochemical performance
Reference characteristics for our aluminium alloy anodes.
- Test environment
- Seawater at 23 °C
- Reference electrode
- Silver / silver chloride (Ag/AgCl)
- Open-circuit potential
- More negative than −1.10 V vs Ag/AgCl
- Closed-circuit potential
- More negative than −1.05 V vs Ag/AgCl
- Electrochemical capacity
- 2,550 – 2,750 Ah/kg
Performance note
Values apply to aluminium alloy anodes in seawater at 23 °C. In-service performance also depends on alloy chemistry, temperature, current demand and anode geometry, so final design values should always come from the approved cathodic protection (CP) design.
Applications
Oil and gas platforms
Submerged structural steel on offshore production facilities.
Jacket structures
Legs, braces and nodes on fixed jacket substructures.
Marine structures
Other seawater-exposed steel structures.
Offshore infrastructure
Engineered anode systems for selected offshore assets.
Manufacturing and quality
A controlled route from your drawing to a documented, ready-to-install anode.
-
01
Engineering review
We review your drawings, CP design and specification, and confirm alloy, net weight, insert design and tolerances before production.
-
02
Insert preparation
Steel inserts are cut, formed and surface-prepared to the approved design for a secure bond with the anode.
-
03
Melting and chemistry control
Each melt is prepared to the specified alloy, and its chemistry is checked against the required limits before casting.
-
04
Casting
Anodes are cast to the required shape and net weight, with the insert soundly embedded.
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05
Inspection and testing
Visual, dimensional and weight checks, plus chemical analysis and electrochemical testing where the specification requires them.
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06
Documentation and dispatch
Anodes are identified, packed for safe transport and supplied with the agreed test records.
Inspection and documentation follow the project's inspection and test plan (ITP). Read about our approach to quality.
Frequently asked questions
What are jacket anodes?
Sacrificial anodes fitted to offshore jacket structures and platforms. They corrode in place of the steel, protecting submerged members from corrosion in seawater.
Which materials are available?
Aluminium alloy and zinc alloy, selected to suit the application, CP design and project specification.
Which aluminium specifications do you supply?
Galvalum III equivalent, DNV / ISO, Alanode or your approved client specification.
What capacity do aluminium jacket anodes deliver?
Our reference data gives 2,550–2,750 Ah/kg for aluminium anodes in seawater at 23 °C.
Can you manufacture to our specification?
Yes. Alloy, dimensions, configuration and inserts are produced to your approved project and client specifications.
Where are jacket anodes used?
On offshore jackets, platforms, submerged marine structures and other steel assets that need sacrificial cathodic protection.
Need jacket anodes for your project?
Send us your alloy, dimensions, quantities, design life or CP specification, and our team will prepare a proposal.
Helpful to include
- Structure drawings and anode layout
- CP design or calculation report
- Alloy and specification
- Anode net weight and dimensions
- Insert design
- Quantity and delivery schedule
