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Author: Site Editor Publish Time: 2025-06-05 Origin: Site
Marine engineering is one of the most demanding sectors when it comes to materials performance. The combination of seawater, high humidity, salt-laden air, and varying temperatures creates an extremely corrosive environment. In these settings, standard materials such as carbon steel and even conventional austenitic stainless steel often fall short in terms of longevity and resistance to degradation. This is where duplex steel proves to be a game-changer.
Duplex steel, known for its unique microstructure that combines the beneficial properties of austenitic and ferritic stainless steels, is increasingly being used in marine applications. Its excellent mechanical strength, high resistance to corrosion, and cost-effectiveness over its life cycle make it an ideal candidate for challenging offshore and coastal projects.
Before examining specific use cases, it’s essential to understand what sets duplex steel apart in marine settings.
Duplex steel offers outstanding resistance to various forms of corrosion common in marine environments:
Pitting and crevice corrosion from chloride-rich seawater
Stress corrosion cracking under tensile stress in salty and humid conditions
Uniform corrosion from constant exposure to moisture and chemicals
These advantages make duplex stainless steels like 2205, S31803, and S32750 ideal for long-term performance near or under the sea.
Duplex steel has nearly twice the yield strength of standard austenitic stainless steels. This allows engineers to use thinner sections without compromising structural integrity, reducing overall weight and material cost—an especially important factor in shipbuilding and offshore platforms where every kilogram counts.
Although duplex stainless steel may come with a higher initial price than some other materials, its extended lifespan, minimal maintenance needs, and lower risk of failure lead to significantly reduced total ownership costs over time.
Modern ships must withstand aggressive marine exposure while remaining reliable and efficient. Duplex steel plays a critical role in ensuring durability and safety across various components.
Ship decks and superstructures face constant assault from sun, rain, salt spray, and mechanical wear. Duplex steel’s ability to resist pitting, crevice corrosion, and environmental fatigue makes it an ideal material for:
Main decks
Bulkheads
External handrails and ladders
Structural reinforcements
The high mechanical strength also improves structural stiffness, leading to better performance in harsh sea conditions.
Components like propeller shafts, rudders, and steering gear require both high strength and corrosion resistance. Duplex steel provides a balanced solution, ensuring:
Reduced risk of fatigue failure from dynamic loads
Protection against erosion-corrosion from cavitation and saltwater turbulence
Longevity in submerged and partially submerged conditions
Grades like SAF 2507 (super duplex) are often used in these critical, load-bearing components.
Seawater-based piping systems for cooling, fire suppression, and ballast often suffer from internal corrosion. Using duplex steel prevents scaling, biofouling, and corrosion-induced leaks, improving safety and reducing downtime.
Offshore oil rigs, gas platforms, and wind farms operate under extreme pressure, salinity, and mechanical loading. Duplex steel is vital in the construction and maintenance of these facilities.
Risers are conduits that carry hydrocarbons from the seabed to surface platforms. Duplex steel’s strength and corrosion resistance make it the material of choice for:
Dynamic risers exposed to high-pressure fluid flow
Flowlines transporting corrosive hydrocarbons, including those containing CO₂ or H₂S
Umbilicals and connectors subjected to repeated stress
Its resistance to stress corrosion cracking is particularly critical for high-pressure applications in deep-sea environments.
Subsea pipelines must remain structurally sound while transporting fluids for long distances under harsh conditions. Duplex steel enables thinner, lighter, and stronger pipeline systems, reducing:
Installation complexity and cost
Environmental risks from leakage
Maintenance requirements over decades of operation
Grades like S31803 and S32760 offer an optimal balance between cost and performance.
The substructure of offshore platforms—called jackets—consists of complex lattice frameworks. Duplex steel is used here to withstand:
Cyclic wave loading and storm surges
Tidal forces and shifting seabed conditions
Long-term exposure to corrosive seawater
Its use not only ensures structural integrity but also reduces the need for protective coatings or cathodic protection systems.
Desalination plants turn seawater into drinkable freshwater through processes like reverse osmosis and thermal evaporation. These processes are highly corrosive due to high salt concentration and aggressive chemicals used for scaling and fouling prevention.
Duplex steel is used extensively in:
High-pressure pumps and casings
Membrane housings and brackets
Concentrate and permeate piping
It ensures resistance to chloride stress cracking, a common failure mode in RO systems made with standard stainless steels.
Thermal desalination methods (like Multi-Stage Flash or Multi-Effect Distillation) expose materials to hot brine and chemical treatment agents. Duplex steel’s thermal and chemical resistance enables long service lives for:
Heat exchangers
Brine heaters
Evaporator tubes
This reduces replacement frequency, improves thermal efficiency, and minimizes scaling.
After desalination, the remaining brine must be discharged back into the sea. These pipelines handle extremely saline and hot effluents, and duplex steel ensures that:
The structural integrity is maintained over time
Environmental compliance is achieved through leak-proof systems
With the global push for sustainable energy, marine renewables such as offshore wind, wave, and tidal energy systems are growing. Duplex steel plays a vital role in:
Monopiles and jackets for wind turbines must survive decades in corrosive offshore conditions. Duplex steel helps reduce fatigue cracking and corrosion failures, offering:
Minimal maintenance over time
Reduced installation cost through weight savings
Compatibility with environmentally friendly coatings
These systems operate in dynamic sea conditions, often fully submerged. Components made of duplex steel maintain performance despite continuous cyclic loading and saline immersion.
Duplex steel also finds application in less visible but critical marine systems.
Duplex steel resists corrosion and fouling in high-volume intake pipes, filters, and cooling lines, improving energy efficiency and plant uptime.
Reliable during emergencies, duplex steel ensures rust-free operation and consistent pressure flow even after years of service in humid ship environments.
Chains, shackles, bollards, and winches benefit from duplex steel’s tensile strength and resistance to salt spray and mechanical wear.
Several duplex steel grades are tailored for marine engineering, each with specific strengths:
UNS S31803 (2205): Balanced corrosion and mechanical performance; widely used in shipbuilding and offshore applications.
UNS S32750 / S32760 (Super Duplex): Higher corrosion resistance and strength; suitable for risers, subsea pipelines, and chemical handling.
UNS S32304 (Lean Duplex): Lower nickel content and cost-effective; ideal for less critical components exposed to mild marine conditions.
Selecting the right grade ensures performance longevity, safety, and cost control in complex marine environments.
As marine engineering advances—from offshore energy to desalination—duplex steel continues to prove itself as the optimal material for durability, corrosion resistance, and long-term performance in challenging ocean environments. Its superior mechanical strength and lifecycle cost savings make it essential for shipbuilding, offshore platforms, and other marine applications.
To ensure the highest quality duplex stainless steel for your marine projects, we recommend working with a trusted manufacturer. Zhejiang Xintongda Special Steel Manufacturing Co., Ltd. offers expertly engineered duplex steel products tailored for demanding industrial and marine environments. Visit www.xtd-stainless.com to explore their product range or contact their team directly to discuss your specific requirements.
