2205 vs 2507 Duplex: Grade Comparison

Grades 2205 and 2507 are the most widely specified duplex and super duplex stainless steels in the oil and gas, chemical, and desalination industries. Both are dual-phase (austenite-ferrite) alloys with high strength and excellent corrosion resistance, but 2507 provides a significantly higher PREN and yield strength at a proportionally higher cost.

Comparison Table

Property	2205 (S32205)	2507 (S32750)
UNS	S32205	S32750
Classification	Standard duplex	Super duplex
Chromium	22.0-23.0%	24.0-26.0%
Nickel	4.5-6.5%	6.0-8.0%
Molybdenum	3.0-3.5%	3.0-5.0%
Nitrogen	0.14-0.20%	0.24-0.32%
PREN (typical)	34-36	42-43
Tensile strength (min)	620 MPa (90 ksi)	795 MPa (116 ksi)
Yield strength (min)	450 MPa (65 ksi)	550 MPa (80 ksi)
Elongation (min)	25%	15%
Hardness (max)	293 HBW	310 HBW
Ferrite content	40-60%	40-60%
Pipe spec	ASTM A790 S32205	ASTM A790 S32750
Forging spec	ASTM A182 F51 / F60	ASTM A182 F53
Max service temp	315°C (600°F)	315°C (600°F)
CPT (critical pitting temp)	~35°C in 6% FeCl3	~65°C in 6% FeCl3
Relative cost	Baseline	30-50% premium

Key Differences

Corrosion Resistance

The PREN gap between 2205 (~35) and 2507 (~42) translates directly into a higher critical pitting temperature (CPT). In standardized ferric chloride testing per ASTM G48, 2205 typically resists pitting up to 35°C, while 2507 resists pitting up to 65°C. This 30°C margin determines which environments each grade can handle safely.

In practice, 2205 is suitable for seawater systems at ambient temperature (without crevices), moderate-chloride process streams, and mildly sour oil and gas production. Grade 2507 is specified for hot seawater, high-chloride brines in desalination, aggressive chemical environments (sulfuric acid, chlorinated organic solvents), and subsea production systems where combined chlorides and H2S/CO2 exceed 2205 limits.

Mechanical Strength

Grade 2507 offers approximately 22% higher yield strength (550 vs. 450 MPa) and 28% higher tensile strength (795 vs. 620 MPa). For pressure-containing applications, this allows thinner wall sections at the same design pressure, reducing weight and partially offsetting the higher per-kilogram cost. This is particularly valuable for subsea pipelines and deepwater risers where weight is critical.

Weldability

Both grades require controlled heat input (typically 0.5-2.5 kJ/mm) and nitrogen-enriched shielding gas (N2 + Ar) to maintain proper austenite-ferrite balance. Grade 2507, with its higher alloy content, is more sensitive to intermetallic precipitation (sigma and chi phases) if heat input is excessive or interpass temperatures exceed 150°C. Welding procedure qualification for 2507 requires stricter controls and more extensive testing.

Pro Tip

Always verify the ferrite content of 2205 and 2507 weldments. The acceptable range is 30-70% ferrite (ideally 40-60%) in both the weld metal and HAZ. Ferrite counts below 30% indicate insufficient nitrogen pickup; counts above 70% indicate insufficient heat input or excessively fast cooling.

Cost Considerations

Grade 2507 costs 30-50% more per kilogram than 2205 due to its higher nickel, chromium, and molybdenum content. However, the higher strength allows thinner walls, which can reduce the net material cost difference to 15-25% on a per-meter basis for pipe. Fabrication costs are also higher due to stricter welding requirements and more extensive non-destructive testing.

For detailed specifications on duplex and super duplex pipe products, refer to the full guide to stainless and duplex pipes.

Read the full guide to stainless steel pipes