Introduction: The Harsh Reality of Marine Corrosion
Offshore wind platforms are situated in some of the most corrosive environments on earth. According to research data published in 2010 by the journal Thermosetting Resin , steel with a thickness of 6.35mm in the marine splash zone can perforate within 5 years, while the design service life for offshore steel structures is generally required to be 20-30 years. This data highlights the core contradiction in material selection for steel grating on offshore wind platforms: how to achieve a service life matching the main platform structure under extreme corrosive conditions?
The “Code for Anti-Corrosion Design of Offshore Wind Power Projects” (NB/T 10626—2021) , issued by the National Energy Administration in 2021, explicitly states that anti-corrosion design for offshore wind farm steel structures must consider the dual constraints of lifecycle cost and environmental corrosivity category. Based on this code and the ISO 12944 series , this article systematically compares the technical performance and service life differences of hot-dip galvanized steel grating, stainless steel grating, and composite material grating in marine environments.
Chapter 1: Marine Environmental Corrosion Zones and the Challenges Faced by Steel Grating
1.1 Marine Corrosion Environmental Zones (ISO 12944-2 & NB/T 10626—2021)
| Corrosion Zone | Environmental Characteristics | Corrosion Rate (Relative) | Main Application Scenarios for Steel Grating |
|---|---|---|---|
| Marine Atmospheric Zone | High salt spray, high humidity, solar radiation | Medium | Upper platform structures, top of wind turbine foundation |
| Splash Zone | Alternating Wet and Dry Conditions, wave impact, ample oxygen supply | Extremely High | Platform base supports, boat landing components |
| Tidal Zone | Periodic immersion, biofouling | High | Foundation transition piece |
| Fully Immersed Zone | Continuous immersion, oxygen concentration differentials | Medium | Lower jacket structure |
| Mud Zone | Oxygen-deprived environment, sulfate-reducing bacteria | Low | Buried pile section |
Key Conclusion: The splash zone is the most severely corrosive area. Steel grating installed in this zone must adopt the highest level of anti-corrosion protection.
Chapter 2: Anti-corrosion Performance and Service Life Comparison of Three Mainstream Materials
2.1 Hot-Dip Galvanized Steel Grating
Technical Standard: GB/T 13912-2020 “Metallic coatings—Hot dip galvanized coatings on fabricated iron and steel articles—Specifications and test methods”
Corrosion Protection Mechanism: The zinc layer acts as a sacrificial anode, corroding preferentially to protect the base steel.
Service Life Expectancy (Based on ISO 1461 and NB/T 10626—2021) :
| Environmental Zone | Zinc Coating Thickness | Expected Service Life | Data Source/Justification |
|---|---|---|---|
| Marine Atmospheric Zone | ≥100μm | 15-20 years | ISO 1461, Appendix C |
| Splash Zone | ≥120μm + seal coat | 8-12 years | NB/T 10626—2021, Clause 5.3 |
| Fully Immersed Zone | Not recommended for standalone use | — | — |
Limitations Analysis:
Research presented in the “Proceedings of the Fifteenth China Ocean (Shore) Engineering Academic Symposium” (2011) points out that anti-corrosion schemes in offshore engineering projected for 20 years of effectiveness can fail within a few years of actual service. The accelerated consumption of hot-dip galvanizing in the splash zone is primarily due to:
Wet/dry alternation accelerating electrochemical corrosion
Wave impact causing mechanical wear of the coating
Chloride Ion Penetration and Destruction of the Passive Film
2.2 Stainless Steel Grating (316L / 2205 Duplex)
Technical Standards: ASTM A240 / ASTM A276
Corrosion Protection Mechanism: Alloying elements (Cr, Ni, Mo) form a dense passive film resistant to chloride ion attack.
Service Life Expectancy (Based on ISO 12944 and Engineering Practice Data):
| Material | Applicable Environment | Expected Service Life | Maintenance Requirement |
|---|---|---|---|
| 316L Austenitic Stainless Steel | Marine Atmospheric Zone, Fully Immersed Zone | 25+ years | Essentially maintenance-free |
| 2205 Duplex Stainless Steel | Splash Zone, High-stress areas | 30+ years | Maintenance-free |
Technical Notes:
316L performs excellently in marine atmospheric environments, but pitting corrosion may occur under long-term immersion conditions in the splash zone.
2205 Duplex Steel, with 22% chromium and over 3% molybdenum, has a Pitting Resistance Equivalent Number (PREN) >35, making it ideal for the splash zone
2.3 Composite Material Steel Grating
Technical Solution: Carbon steel substrate + thermal sprayed metal (zinc/aluminum) + seal coat
Technical Standards: ISO 2063 “Thermal spraying—Zinc, aluminium and their alloys”
Research Data Support:
A study published in China Surface Engineering , Issue 2, 2005, indicated that offshore steel structures using long-lasting composite protective coatings can achieve a protective life of over 10 years. Furthermore, systems using zinc-aluminum composite spraying (ZnAl15) plus an epoxy seal coat are recommended in the ISO/CD 25249-2 (2025 draft) for primary steel components of offshore wind structures.
Service Life Expectancy:
| Composite Solution | Coating System | Expected Service Life | Applicable Environment |
|---|---|---|---|
| Thermal Sprayed Aluminum + Epoxy Seal | 150μm Al + 2 coats Epoxy | 15-20 years | Splash Zone |
| Zn-Al Composite Spray + Polyurethane Topcoat | 120μm ZnAl15 + 80μm Polyurethane | 20-25 years | All Marine Zones |
2.4 Service Life Comparison Summary Table
| Material Type | Marine Atmospheric Zone | Splash Zone | Fully Immersed Zone | 25-Year Total Cost (Index) |
|---|---|---|---|---|
| Hot-dip Galvanized (100μm) | 15-20 years | 8-12 years | Not Recommended | 1.0 (Baseline) |
| Hot-dip Galvanized + Heavy-duty Coating | 20-25 years | 12-15 years | 10-12 years | 1.4-1.6 |
| 316L Stainless Steel | 25+ years | 20-25 years | 25+ years | 2.3-2.8 |
| 2205 Duplex Stainless Steel | 30+ years | 30+ years | 30+ years | 3.0-3.5 |
| Thermal Sprayed Al + Seal Coat | 20-25 years | 15-20 years | 15-20 years | 1.8-2.2 |
Chapter 3: Q&A: Common Questions in Steel Grating Selection for Offshore Wind
Q1: Must steel grating for offshore wind platforms be stainless steel?
A: Not necessarily; it depends on the installation location. According to NB/T 10626—2021 , Clause 4.2, anti-corrosion design shall be determined comprehensively based on the environmental zone of the structure, design service life, and maintenance conditions.
Marine Atmospheric Zone (upper platform): Hot-dip galvanizing (≥100μm) +Regular maintenance is feasible
Splash Zone (lower platform): Stainless steel or composite coating solutions MUST be used, as the service life of hot-dip galvanizing in this zone is less than 15 years
Q2: How long can hot-dip galvanized steel grating last in a marine environment?
A: Based on ISO 1461 and multiple engineering data sources:
Marine Atmospheric Zone: 15-20 years (zinc consumption rate 1-2μm/year)
Splash Zone: 8-12 years (zinc consumption rate 3-5μm/year)
Fully Immersed Zone: 5-8 years (accelerated by galvanic corrosion)
Q3: What are the advantages of composite steel grating compared to stainless steel?
A: The main advantage of composite solutions is lower initial cost (approximately 60-70% of 316L), and with proper design, they can achieve over 20 years of life in the splash zone. However, disadvantages include:
High requirements for construction quality control
Difficult repair after on-site damage
Need for recoating after coating aging
Q4: Does steel grating on offshore wind platforms need to consider typhoon loads?
A: Yes, it must be considered. According to design practices for offshore wind and relevant codes, steel grating design must simultaneously satisfy:
Structural loads: Uniformly distributed load ≥3.0kN/m², Concentrated load ≥1.5kN
Wind resistance: Must be calculated for wind uplift force, with no fewer than 4 fixing points per panel, using anti-lift clips
Chapter 4: Lifecycle-Based Selection Recommendations
4.1 Recommended Solutions by Corrosion Zone (Based on NB/T 10626—2021)
| Corrosion Zone | Recommended Material/Solution | Minimum Thickness Requirement | Fixing Requirements |
|---|---|---|---|
| Marine Atmospheric Zone | Hot-dip Galvanized (≥100μm) or 316L | Bar 40×5mm | Stainless Steel M10 Bolts |
| Splash Zone | 2205 Duplex Stainless Steel or Thermal Sprayed Al + Heavy-duty Coating | Bar 40×5mm (consider thickening) | Duplex Steel Bolts, Lock Washers |
| Tidal Zone / Fully Immersed Zone | 2205 Duplex Stainless Steel | Bar 50×5mm (consider biofouling weight) | Underwater-Specific Fasteners |
4.2 Economic Analysis (25-Year Lifecycle)
| Selection Option | Initial Cost | Maintenance Frequency In 25 Years | 25-Year Total Cost Index | Suitability Rating (Splash Zone) |
|---|---|---|---|---|
| Hot-dip Galvanized | 1.0 | 2 times (Years 12, 20) | 1.8-2.2 | ★☆☆ (Not Recommended) |
| Hot-dip Galvanized + Heavy-duty Coating | 1.4 | 1 time (Year 15) | 1.6-1.9 | ★★☆ (Use with Caution) |
| 316L Stainless Steel | 2.5 | 0 | 1.3-1.6 | ★★★ (Recommended) |
| 2205 Duplex Stainless Steel | 3.2 | 0 | 1.5-1.8 | ★★★★ (Strongly Recommended) |
| Thermal Sprayed Al Composite Coating | 1.8 | 1 time (Year 18) | 1.7-2.0 | ★★★ (Recommended, requires high-quality application) |
Analysis Conclusion (Based on ISO 15686-5 Life Cycle Costing theory):
In highly corrosive areas like the splash zone, stainless steel solutions of grade 316L and above offer the optimal lifecycle cost
Although hot-dip galvanizing has a lower initial cost, requiring 1-2 replacements within 25 years results in a total cost comparable to or higher than stainless steel
Chapter 5: Conclusion and bangtu Company's Technical Commitment
The selection of steel grating for offshore wind platforms is a comprehensive decision based on environmental corrosivity category, design life requirements, and lifecycle cost. According to the technical requirements of the National Energy Administration’s NB/T 10626—2021 and international standards ISO 12944 and ISO 1461 :
In marine atmospheric zones, hot-dip galvanized steel grating (coating thickness ≥100μm) can be used, but a regular inspection and maintenance mechanism must be established.
For the Splash Zone and below, 316L or 2205 Duplex stainless steel grating is the reliable choice to ensure a 25-year design life.
Composite material solutions can be considered as an economical alternative, but construction quality must be strictly controlled, and maintenance access routes must be reserved.
About bangtu Company
Bangtu Company has been deeply involved in the steel grating industry for over 20 years, with products widely used in domestic and international offshore wind farm platforms, petrochemical refining projects, and marine engineering equipment.We commit to:
Providing third-party material test reports and salt spray test data (according to GB/T 10125) for all product lines.
Sourcing marine-grade stainless steel grating from Baowu / Taigang original 316L/2205 Duplex steel, with 100% traceability.
Offering technical selection services based on the project’s specific corrosive environment, assisting EPC contractors in preparing anti-corrosion technical specifications.
Choose bangtu, choose a 25-year reliable commitment.
Tel/Whatsapp: +8613363180165
Email: james@bangtuwiremesh.com
Website: www.bangtusteelgrating.com | www.chinawiremesh.ru
Appendix: Referenced Standards and Literature
ISO 12944 (all parts) “Paints and Varnishes—Protective Paint Systems for Steel Structures Against Corrosion.”
ISO 1461 “Hot-Dip Galvanized Coatings on Steel Articles—Technical Requirements.”
- ISO/CD 25249-2 , Corrosion protection of offshore wind structures — Part 2: Primary steel components, 2025 Draft.
