ASME SA240 S32205 Duplex Stainless Steel Plate Guide

1. What Is ASME SA240 S32205 Plate?

ASME SA240 (identical in technical content to ASTM A240) covers chromium and chromium-nickel stainless steel plate, sheet and strip for pressure vessels and general applications. Grade S32205, marketed as 2205 duplex, is a two-phase alloy with roughly 50/50 austenite and ferrite in the annealed condition. The duplex structure combines the high strength of ferritic steel with the toughness and corrosion resistance of austenitic steel: minimum yield strength of 450 MPa, roughly twice that of 316L, and pitting resistance equivalent to a PREN of about 35.

The designation UNS S32205 is the controlled version of the older UNS S31803. Both are known commercially as 2205, but S32205 carries tighter ranges: chromium 22.0-23.0% (versus 21.0-23.0%), molybdenum 3.0-3.5% (versus 2.5-3.5%) and nitrogen 0.14-0.20% (versus 0.08-0.20%). The German steel number is 1.4462 per EN 10088-2.

2. Chemical Composition per ASTM A240/A240M

Element	S32205, %
Carbon, C	0.030 max
Manganese, Mn	2.00 max
Silicon, Si	1.00 max
Phosphorus, P	0.030 max
Sulfur, S	0.020 max
Chromium, Cr	22.0-23.0
Nickel, Ni	4.50-6.50
Molybdenum, Mo	3.0-3.5
Nitrogen, N	0.14-0.20
Iron, Fe	Balance

The nitrogen addition is critical: it stabilizes austenite, raises strength and markedly improves pitting corrosion resistance. With the mid-range composition above, the pitting resistance equivalent number, PREN = Cr + 3.3 x Mo + 16 x N, calculates to roughly 35, which is the accepted design basis for 2205 in chloride service.

3. Physical and Mechanical Properties

Density: 7.805 g/cm3 (0.285 lb/in3)

Melting range: 1420-1465 deg C (2588-2669 deg F)

Minimum tensile strength (A240): 655 MPa (95 ksi)

Minimum 0.2% yield strength (A240): 450 MPa (65 ksi)

Minimum elongation: 25%

Practical service range: about -50 deg F to 600 deg F (-45 deg C to 315 deg C); above about 315 deg C the ferrite phase embrittles on long exposure

Plates are supplied in the annealed condition; ASME SA240 requires solution annealing at a minimum temperature of 1900 deg F (1040 deg C) followed by rapid quenching for duplex grades. Hot-rolled plates can be further strengthened by heat treatment at the cost of surface finish, while cold-rolled sheets gain strength from cold work and show a smoother surface.

4. S32205 vs S31803: Which One Is on Your Order?

Both designations appear in 2205 specifications. S31803 was the original grade with wider limits; S32205 is the refined composition that most mills now produce. The practical differences for the buyer:

Property	S32205	S31803
Chromium	22.0-23.0%	21.0-23.0%
Molybdenum	3.0-3.5%	2.5-3.5%
Nitrogen	0.14-0.20%	0.08-0.20%
Typical PREN	about 35	about 33-35

When a project drawing states S32205, plate supplied to S31803 is technically a different material; always verify the UNS number on the certificate. In practice S32205 is the standard 2205 grade supplied worldwide.

5. Applications of SA240 Type 2205 Plate and Sourcing

Chemical process vessels, piping and heat exchangers handling chlorides and organic acids

Seawater pipelines and marine structures where pitting and crevice corrosion are the failure modes

Pulp mill digesters, bleach washers and chip pre-steaming vessels

Flue gas desulfurization (FGD) equipment in power plants

Oil field piping, separators and heat exchangers, and food processing equipment

Because duplex plate has roughly twice the yield strength of 316L, section thickness can often be reduced by 30-50% for pressure-containing components, which offsets the higher per-kg price. Verify the design temperature range before substitution: duplex grades are not recommended for continuous service above 315 deg C.

For pressure vessel plate, request the mill test certificate per EN 10204 type 3.1 showing heat number, chemical analysis and mechanical results. Third-party inspection reports from international agencies are available on request, and PMI (positive material identification) checks should cover chromium, nickel and molybdenum. Plate is stocked in thicknesses from 4.5 mm to 152 mm and can be cut to size; surface options include hot-rolled, annealed and pickled, 2B and No.1 finishes.

6. FAQ

Is S32205 the same as 2205 duplex stainless steel?

Yes. 2205 is the commercial name; UNS S32205 and W.Nr 1.4462 are the standard designations. Some older documents specify UNS S31803, which has wider composition limits but is otherwise the same family.

What is the PREN of S32205?

With the controlled composition of S32205, PREN = Cr + 3.3 x Mo + 16 x N works out to about 35, giving pitting resistance clearly above 316L (PREN about 24-26) and similar to 904L in many chloride media.

What is the maximum service temperature of 2205 plate?

Continuous service is normally limited to about 315 deg C (600 deg F). Above this temperature, sigma phase precipitation can embrittle the material. Minimum design temperature is about -45 deg C for most applications.

Can S32205 plate be welded without filler?

Duplex grades require matching duplex filler metal (e.g., ER2209) to maintain the austenite/ferrite balance in the weld. Autogenous welding without filler produces excessive ferrite and should be avoided for load-bearing joints. Preheat is normally not required.

Why is 2205 plate more expensive than 316L?

Higher alloy content (molybdenum, nitrogen and controlled nickel) and tighter process control raise the cost. The higher yield strength allows thinner sections, so the total project cost is often competitive or lower in chloride service where 316L would fail early.