A full-dimensional analysis of corrosion-resistant alloy materials for ships: material selection strategies and performance comparison
Release time:
2025-06-26
Ships face multiple challenges such as seawater corrosion, microbial attachment, high humidity and high salt in the marine environment for a long time. Material selection directly determines the life and safety of ships. This article will systematically analyze the performance differences between mainstream corrosion-resistant alloy steels and alternative materials, and provide a selection guide.
1. Ship corrosion environment and material failure mechanism
Seawater electrolyte corrosion
As a complex electrolyte solution, seawater is rich in Cl⁻, dissolved oxygen and microorganisms, which cause electrochemical corrosion to metals. The average annual corrosion rate of ordinary carbon steel in the marine environment can reach 0.1–0.5mm, and the local pitting depth can even exceed 5mm.
Cargo oil tank acid corrosion
Sulfur compounds in crude oil decompose to form H₂S, which combines with condensed water to form strong acid (pH can be as low as 1), causing hydrogen permeation cracking of carbon steel. Tests show that traditional steel plates can form 6.3mm corrosion pits on the bottom plate of the oil tank within 2 years.
High temperature and high pressure corrosion
The temperature of parts such as the engine exhaust system exceeds 600℃, and the material needs to have both high temperature strength and oxidation resistance.
2. Performance comparison and application scenarios of mainstream corrosion-resistant materials
(I) Nickel-based alloys: the first choice for harsh environments
By optimizing the proportion of elements such as chromium and molybdenum, nickel-based alloys perform well in reducing/oxidizing media:
Alloy grade Key features Ship application scenarios Corrosion resistance advantages
Inconel 625 Cr≈20%, Mo≈9% Exhaust system, propeller shaft Resistant to seawater erosion corrosion, resistant to high temperature oxidation
Monel 400 Ni≈63%, Cu≈30% Valves, pump bodies, seawater pipelines Resistant to seawater pitting and stress corrosion cracking
NS337 Mo≥15%, Cr≥15% Nuclear power cabins, submersible components Resistant to boiling hydrochloric acid, resistant to 650℃ high pressure
Case: Hastelloy C-276 (same as NS337) is used in nuclear-powered ship cooling systems. The stress corrosion cracking rate in Cl⁻-containing media is only 1/10 of that of austenitic stainless steel.
(II) Special corrosion-resistant steel for ships: revolutionary material for tanker cargo holds
Japanese companies add copper, nickel, tin and other elements to form a dense protective film on the surface of steel:
NSGP-1 of Nippon Steel: Cu+Ni+Sn composite addition, the corrosion rate is reduced to 1/5 of that of traditional steel, and the actual ship is maintenance-free for 10 years;
JFE-SIP-OT: Optimized Cr/Mo ratio, the pitting depth is only 65% of that of ordinary coated steel plates;
Wuhan Iron and Steel cargo oil tank steel: When Cu≥0.3%, 100–500nm copper deposition particles are generated on the surface, reducing the corrosion current density by 80%.
(III) Copper alloy and aluminum alloy: cost-effective choice for specific components
C28000 brass (60Cu-40Zn):
The first choice for propellers and condensers, relying on the surface oxide film to resist seawater corrosion, the service life is extended by 3 times that of carbon steel;
Balanced mechanical properties (tensile strength ≥300MPa), easy to cast complex blade shapes
5083 aluminum alloy (4.5Mg-0.7Mn):
Density is only 2.7g/cm³, which can reduce the weight of superstructure by 30% and improve fuel efficiency by 15%;
H116 state has the best exfoliation corrosion resistance and is suitable for hull side plates.
III. Material selection decision matrix: performance, cost and process balance
Environmental adaptability principle
High temperature components (>500℃) → nickel-based alloys (such as Inconel 718);
Crude oil tank/ballast tank → Cu/Ni alloyed corrosion-resistant steel (such as NSGP-1);
Parts in direct contact with seawater → C28000 copper alloy or super duplex steel.
Full life cycle cost accounting
Initial cost: aluminum alloy < low alloy steel < nickel-based alloy (price difference can reach 5 times);
Maintenance cost: NSGP-1 steel is free of painting, saving $1.2 million/ship in maintenance costs in 10 years.
Processing technology constraints
Nickel-based alloys require laser/TIG welding, and ordinary shipyards need to upgrade equipment 1;
5083 aluminum alloy has a strength retention rate of >90% after welding, which is suitable for on-site construction.
IV. Technological frontier: environmentally friendly and intelligent materials
Self-repairing coating alloy
Kobe Steel has developed a new Cr-Mo steel, which can automatically increase the pH value in the pitting pit and reduce the corrosion rate to 1/56 of traditional steel.
Digital corrosion monitoring
Implant sensors to monitor the rust thickness of NSGP steel in real time, and combine big data to predict the replacement cycle.
Trend judgment: IMO 2025 new regulations require oil tankers to use certified corrosion-resistant steel. Japanese materials still dominate, but the localization process of Wuhan Iron and Steel, Baosteel and other companies is accelerating.
Conclusion: Material selection needs to break the "cost-only theory"
Ship materials need to strike a balance between corrosion safety margin, process feasibility and full-cycle cost. It is recommended that nickel-based alloys be used for key parts of high-value ships (LNG ships, military ships); alloyed corrosion-resistant steel is preferred for commercial tankers; and aluminum alloy + C28000 combination can be used for offshore boats. With the gradual mass production of China's NSGP-1 grade steel (such as Wuhan Iron and Steel models), the application cost of corrosion-resistant steel is expected to be reduced by more than 30%.
Industry warning: In 2024, a bulk carrier penetrated the bulkhead due to long-term pitting corrosion of Mn-based steel. The accident analysis confirmed that Ni-Cr steel was better than Mn-based steel in short-term hanging plate tests, but Mn-based steel actually performed better in a long-term uncoated environment. Therefore, material verification needs to be combined with actual ship conditions!
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