Challenges and innovations of duplex stainless steel in marine engineering

1. Introduction
Background: The harshness of the marine environment (high salinity, high pressure, microbial corrosion, etc.) places extreme demands on material properties.

Advantages of duplex stainless steel (DSS):

Synergistic effect of two phases (austenite + ferrite): high strength (ferrite) and corrosion resistance (austenite).

Compared with traditional materials: better than 304/316 stainless steel, lower cost than nickel-based alloys.

2. Key challenges in marine engineering
Local corrosion risks:

Pitting, crevice corrosion (such as welded joints, bolted joints).

Typical case: Failure of seawater pump valves due to Cl⁻ penetration.

Stress corrosion cracking (SCC):

Synergistic effect of high stress + hot and humid environment (such as deep-sea pipelines).

Biofouling and microbial corrosion (MIC):

Sulfate-reducing bacteria (SRB) accelerate material degradation.

Welding process problems:

The phase ratio of the heat-affected zone (HAZ) is unbalanced, resulting in decreased corrosion resistance.

3. Innovative solutions and progress
Innovation in material design:

Development of new alloys: such as 2507 super duplex steel (PREN ≥ 40), nitrogen-containing duplex steel (to improve the stability of the passive film).

Microstructure regulation: Optimize the ratio of the two phases through heat treatment (such as 50:50 balance).

Surface treatment technology:

Laser surface alloying and plasma nitriding enhance the corrosion resistance of critical areas.

Welding process optimization:

Low heat input laser welding and pulse TIG welding reduce σ phase precipitation.

Protection technology integration:

Cathode protection + coating composite solution (such as epoxy resin coating + sacrificial anode).

4. Future prospects
Intelligent monitoring: embedded sensors monitor the corrosion status of materials in real time.

Environmentally friendly alloy design: reduce dependence on precious metals (such as Mo) and reduce costs.

Interdisciplinary integration: combining microbiology (inhibiting MIC) and big data (predicting life).

5. Conclusion
Duplex stainless steel is gradually breaking through the limits of marine engineering through the collaborative innovation of composition, process and protection, but it needs to continue to cope with the challenges of emerging scenarios such as deep sea and polar regions.