As wind turbines advance into deeper waters, they face not only stronger winds but also brutal marine corrosion and complex loads. The choice of materials has never been so directly tied to the lifecycle safety and economic return of an offshore wind farm.

Section 1: Sailing into the Deep Blue: Opportunities and Material Challenges for Offshore Wind

• Harsher Conditions: Higher salt spray concentration, more frequent splash zone冲刷, and more complex microbiologically influenced corrosion.
• More Difficult Maintenance: “Accessibility” plummets, leading to exponentially higher single maintenance costs.
• More Complex Loads: Support structures bear greater coupled dynamic loads from wind, waves, and currents, pushing the strength and fatigue performance of connecting components to their limits.

Section 2: Why Duplex Steel? Decoding the “Optimal Material Solution” for Offshore Wind

• Key Metric: PREN Value: The PREN value of 2205 duplex steel is typically above 35, and 2507 exceeds 40, far surpassing that of 316L stainless steel (~25). This ensures long-term resistance to the initiation and propagation of pitting and crevice corrosion in the splash zone and fully immersed areas with high temperatures and chloride concentrations.
• Practical Applications: Critical locations like the transition piece of foundations, tower connection flanges, and seawater cooling system pipe flanges that are directly exposed to seawater.

• Doubled Yield Strength: The yield strength of 2205 duplex steel (≥450MPa) is more than double that of 316L and even exceeds that of ordinary carbon steel. This allows for reduced flange cross-section thickness and weight​ while bearing equivalent loads.
• Direct Benefits: Reduces the weight at the top of the tower and foundation, optimizes overall structural design, lowers logistics and installation costs, and is particularly beneficial for stability control in floating wind turbines.

• The duplex microstructure effectively hinders crack propagation, granting it superior fatigue resistance under long-term cyclic wave and wind loads compared to single-phase steels. Good low-temperature toughness also makes it suitable for cold seas like the North Sea.

• Although welding procedures are more demanding than for ordinary carbon steel, mature Welding Procedure Specifications (WPS) and dedicated filler metals have made its weldability very reliable. While the initial procurement cost is higher, the elimination of periodic corrosion maintenance, avoidance of unplanned downtime, and assurance of a service life exceeding 25 years make its Total Cost of Ownership (TCO) highly competitive.

Section 3: Far Beyond Simple Forging: The Extreme Technical Demands on Offshore Wind Duplex Flanges

• High-Purity Melting: Strict control of harmful elements like S and P is the foundation for ensuring corrosion resistance and toughness. Processes like AOD or VOD refining should be employed.
• Uniform Phase Ratio: Ensuring a near 50:50 ratio of austenite to ferrite phases, avoiding the precipitation of detrimental intermetallic phases, relies on precise chemical composition control and subsequent heat treatment.

• Sufficient Forging Ratio: Adequate forging deformation breaks down the as-cast structure, refines the grain, and increases material density and isotropy of mechanical properties.
• Precise Temperature Control: The forging temperature range must be strictly controlled to prevent overheating or finishing at too low a temperature, which would degrade properties.

• This is the most critical​ step. Solution annealing must be performed at 1020-1150°C (adjusted per grade) followed by rapid water quenching, aiming to:
  1. Dissolve any harmful phases (like sigma phase) that may have precipitated during forging.
  2. Restore the ideal phase balance.
  3. Achieve optimal corrosion resistance.
     JIAJI Forging’s computer-controlled, fully automated heat treatment furnaces ensure each product undergoes an identical, fully traceable heat treatment cycle.

• Offshore wind flanges typically require the highest level of inspection standards, such as:
  • Ultrasonic Testing (UT): Performed according to standards like EN 10228-3 or ASTM A388 to detect internal minute flaws.
  • Penetrant Testing (PT) or Magnetic Particle Testing (MT): 100% inspection of surface and near-surface defects.
  • Rigorous Dimensional and Geometric Tolerance Inspection: Ensures precise fit with tower and foundation components.

• Products must obtain industry-recognized certifications, such as:
  • Wind Industry-Specific Approvals: E.g., component certifications from classification societies like DNV GL, LR for offshore wind.
  • Material & Manufacturing System Certifications: PED 2014/68/EU (Pressure Equipment Directive), ISO 9001, and standards like NORSOK M-650 as specified by clients.
  • Welding Procedure Qualification (PQR/WPS): Demonstrates the manufacturer possesses qualified welding capabilities, crucial for projects requiring weld neck flanges or welded attachments.

Section 4: JIAJI Forging – Your Reliable Partner Who Understands the “Grammar” of Offshore Wind

• Material Understanding Born from Practice: Involved in R&D since the early waves of duplex steel application in China, we possess a profound understanding of material performance limits and failure modes in real marine environments. This enables us to translate standard requirements into precise control points within the manufacturing process.
• A Manufacturing System Built for Extreme Environments: From incoming material verification and CNC contour forging to ensure grain flow, to fully automated heat treatment and comprehensive mechanical & corrosion property testing (including corrosion resistance tests), we have built a closed-loop quality fortress. Key performance indicators of our duplex steel flanges (such as strength, toughness, and CORROTEST results) meet international advanced standards.
• A Different Interpretation of Cost Competitiveness: Through process optimization and scaled production, we effectively control the manufacturing cost of high-performance duplex steel flanges. Compared to top-tier international brands, JIAJI Forging can offer clients 20%-30% savings on comprehensive procurement costs​ while providing equivalent quality and certification assurance, making this long-term insurance affordable for more wind projects.
• A Validated Track Record in Global Projects: Our products have followed Chinese wind turbine OEMs and EPC contractors to over 30 countries and regions worldwide, finding application in offshore wind projects from the East China Sea and South China Sea to the North Sea of Europe, enduring the tests of diverse marine environments.