Is S31803 the Same as 2205? Duplex Designations Explained

The Relationship Between S31803 and 2205

UNS S31803 and 2205 are essentially the same material. 2205 is the generic trade name for the standard duplex stainless steel, while S31803 is its UNS designation, also known as F51 in bar specifications. The material has a roughly 50-50 ferrite-austenite microstructure, high strength, and excellent resistance to pitting and stress corrosion cracking in chloride environments.

The Improved S32205

An improved version, UNS S32205, applies slightly more stringent composition controls, particularly nitrogen at 0.14 to 0.20 percent and molybdenum at 3.0 to 3.5 percent, resulting in enhanced corrosion resistance. S31803 and S32205 are often used interchangeably in procurement documents, but for critical chloride service the higher minimum properties of S32205 are preferred.

Chemical Composition

Typical limits for the 2205 family are chromium 21.0 to 23.0 percent, nickel 4.5 to 6.5 percent, molybdenum 2.5 to 3.5 percent, nitrogen 0.08 to 0.20 percent, and carbon 0.030 percent maximum, with iron as balance. The composition balances the two phases to achieve both high strength and corrosion resistance.

Mechanical Properties

Minimum properties are tensile strength 620 MPa, yield strength 450 MPa, elongation 25 percent, and impact energy 47 J at minus 46 degrees C. Density is about 7.8 g per cubic centimeter, elastic modulus 200 GPa, and thermal conductivity about 19 W per meter per Kelvin.

Why Duplex Instead of 316

Compared with 316, S31803 has roughly twice the yield strength, and its pitting resistance equivalent number of about 34 versus 25 for 316 means proportionally better pitting resistance. This combination allows thinner, lighter, and more corrosion-resistant equipment.

Applications

The grade is used in offshore oil and gas pipelines, heat exchangers and pressure vessels, marine engineering and desalination plants, pulp and paper equipment, and chemical processing. When purchasing, verify the applicable standard and mill test certificate to confirm the exact grade, S31803 or S32205, and its properties.

Frequently Asked Questions

Q: Are S31803 and 2205 the same?

A: Yes, 2205 is the trade name and S31803 the UNS designation.

Q: What is S32205?

A: The improved duplex with tighter composition control and higher nitrogen.

Q: What is the yield strength of 2205?

A: 450 MPa minimum.

Q: What is the PREN of S31803?

A: About 34, versus 25 for 316.

Q: What applications use duplex 2205?

A: Offshore pipelines, heat exchangers, desalination, and chemical processing.

Q: What sizes are available?

A: Pipes, plates, and fittings from 6 mm diameter and up, customized as required.

Contact us for S31803 and S32205 duplex stainless products with certified mill test reports and material lists.