Guide
Is Duplex 2205 Worth Using Instead of 316 for Pump and Valve Parts?
Duplex 2205 is a stainless steel whose structure is roughly equal parts austenite and ferrite, with more chromium, molybdenum and nitrogen than 316, and a yield strength more than twice that of Type 316. Pump and valve designers reach for it when chloride pitting or stress corrosion cracking is shortening the life of 316 shafts, stems and bodies. The catch is on the shop floor: the same strength that helps in service makes the alloy harder to cut, so the choice is a trade between service life and machining effort, not a free upgrade.
By Saola Manufacturing engineering team · Published · Updated
On this page
Where does duplex 2205 beat 316 on wetted pump and valve parts?
It resists chloride pitting, crevice attack and chloride stress corrosion cracking better than 316, and it is far stronger, which is why it replaces 316 on shafts, stems and bodies that fail in chloride service.
The International Molybdenum Association (IMOA) states that 2205 has pitting and crevice resistance similar to Type 904L, that improved stress corrosion cracking resistance is a primary reason for choosing duplex steels, and that its yield strength is more than twice that of Type 316 (IMOA, duplex stainless steel). A consultant's report prepared for a sight-window maker reaches the same ranking on chloride environments and notes duplex alloys are more resistant to chloride stress corrosion cracking than Types 304 and 316 (Material Selection Resources, 2006).
For a pump or valve OEM this maps onto familiar failures: pitting on a shaft journal in brackish or process water, stem and packing-area crevice attack, and cracking in a stressed part exposed to hot chlorides. The higher strength also lets some designs use less section. IMOA's fabrication guide notes the yield strength may allow the design engineer to decrease wall thickness in some applications (IMOA Practical Guidelines, 3rd ed., 2014).
If your current failures are not chloride-driven, such as wear, galling or fatigue, duplex may not help, and the guide on chloride stress corrosion cracking in stainless is a better place to confirm the mechanism first.
How do the numbers compare?
The headline numbers are a yield strength of 450 MPa minimum for 2205 plate per ASTM limits and a PREN of 35 to 36, against a much lower strength and pitting index for 316.
The table pulls its 2205 values from the IMOA fabrication guide, which tabulates minimum ASTM and EN limits for 2205 plate at 450 MPa (65 ksi) yield and 655 MPa tensile, with EN 1.4462 as the European equivalent of UNS S32205 (IMOA Practical Guidelines, 3rd ed., 2014). The PREN, the pitting resistance equivalent number, is calculated from chromium, molybdenum and nitrogen, and IMOA gives 35 to 36 for S32205 and 33 to 35 for the older S31803 designation. That gap is why the UNS number on your drawing matters.
Do not read the PREN as a promise. The same guide cautions that 2205 does not have enough crevice corrosion resistance to withstand seawater in critical applications, or where deposits or crevices exist, so a tight crevice at a seal or a flange can still be attacked. For those cases the higher-alloyed super duplex grades are the usual next step, and a materials engineer should make that call.
| Property | Duplex 2205 | Austenitic 316 / 304 | Why it matters on a pump or valve part |
|---|---|---|---|
| Yield strength, minimum (plate) | 450 MPa (65 ksi) | Less than half of 2205 for Type 316 (IMOA: 2205 is more than twice Type 316) | Thinner sections possible; higher cutting forces |
| Pitting resistance (PREN) | 35 to 36 for S32205 | Lower than 2205 | Better resistance to chloride pitting |
| Chloride stress corrosion cracking | More resistant | Less resistant | Longer life in hot chloride service |
| Thermal expansion, 20 to 100 °C | 13.0 × 10-6/K | 16.4 × 10-6/K for Type 304 | Less growth with temperature; helps hold size |
| Upper service temperature (ASME allowable stress limit) | 315 °C (600 °F) | Not limited by ferrite embrittlement | Duplex is not for prolonged hot service |
| Machinability with carbide tooling | Lower than 316; higher cutting forces and faster tool wear | Baseline | Cost per part rises with cycle time and inserts |
| Magnetic response | Magnetic (contains ferrite) | Annealed austenitic is essentially non-magnetic | A magnet does not identify the grade |
What changes on the shop floor when you machine duplex instead of 316?
Cutting forces are higher, tools wear faster, chips are strong and hard to break, and the work-hardened layer from one pass can punish the next.
IMOA's fabrication guide describes duplex as typically more difficult to machine than the 300-series austenitic grades of similar corrosion resistance. It says the chip is strong and abrasive to tooling, that the alloys are made with as little sulfur as possible so there is little to aid chip breaking, and that the difference is most noticeable with carbide tooling (IMOA Practical Guidelines, section 11).
Its general machining guidance reads like a setup checklist. Use powerful, rigid machines and mount the tools and the workpiece very rigidly. Keep tool extension as short as possible. Use a sharp-edged, coated carbide insert with positive chip-breaker geometry and a nose radius no larger than necessary. Plan the sequence so each cut goes deeper than the work-hardened layer left by the previous pass. Use enough speed to avoid built-up edge, but not so much that the edge wears rapidly. Flood the cut with coolant, preferably an oil or emulsion with extreme-pressure additives, and change inserts on a schedule. The guide adds that interrupted cuts should be avoided with carbide.
For a shaft or valve stem this affects the process more than the drawing. Long slender parts need steady rests or support, and the finish pass should not be a light skim that rubs on the hardened surface. The cost impact shows up in cycle time and insert consumption, so ask for the quote to be built on the duplex cutting plan, not copied from a 316 quote.
When is 316 still the better choice?
Choose 316 when chloride attack is not the failure mode, when the part runs hot for long periods, or when machining cost and stock availability outweigh the extra service life.
Three situations favor staying with 316. First, if the failures are mechanical or caused by something other than chlorides, duplex adds cost without fixing them. Second, duplex has a service temperature ceiling: IMOA cautions that, because of the danger of 475 °C embrittlement of the ferrite, duplex steels should not be used for prolonged periods above the temperatures allowed by the applicable pressure vessel design code, and its table shows 315 °C for 2205 under the ASME limit (IMOA Practical Guidelines, section 7 and Table 2). Third, if a critical crevice defeats 2205 anyway, a better design detail or a higher alloy beats a switch to 2205.
The voestalpine range sheet also positions duplex 2205 as superior to 304 and 316 in chloride stress corrosion resistance at high strength, and lists UNS S31803 with ASTM A484 and NACE MR0175 references (voestalpine Specialty Metals). If the part is for sour service, check the hardness limits in the guide on NACE MR0175 material hardness before committing to a grade.
For annual volumes in the low tens of thousands, the sensible test is a pilot lot: machine a small run of the part in both grades, compare tool life and cycle time, and weigh the machining premium against the cost of a field failure in the chloride service you are protecting against.
What should the drawing and RFQ say for a duplex part?
Call out the UNS number, the product specification and the solution-annealed condition, and ask for a mill test report with full chemistry so the PREN can be checked.
"Duplex" is not a specification. Write the grade as UNS S32205 (EN 1.4462) rather than 2205, name the ASTM or EN product specification for the stock form, and state the heat-treat condition, which for duplex is solution annealed. ASTM bar and forging specifications that list S32205 are the usual references, such as A276 for bar and A182 for forged fittings and valve parts, and the buyer should confirm the right one for the part. Because the older S31803 designation allows lower alloy levels, IMOA notes that 2205 with a narrower composition range was introduced under S32205 and that S32205 is typical of today's commercial production.
Then ask for the evidence:
- A mill test report with chromium, molybdenum and nitrogen reported, so the PREN is calculated from the actual heat.
- A ferrite or phase-balance requirement if your application needs one; the guide says the favorable properties are achieved when ferrite and austenite are both in the range of 30 to 70 percent, with most production close to equal amounts.
- Material verification on receipt; the guide on PMI with XRF explains what it can and cannot confirm, and note that XRF does not read nitrogen.
- Any corrosion test your application requires, written as a named method with its acceptance criterion, since the test is more informative than the grade name.
Duplex and other stainless bar are not among the materials Saola currently lists as running for CNC turning and CNC milling, so state the grade and stock form on the RFQ and confirm scope at drawing review rather than assuming it.
Frequently asked
Is duplex 2205 magnetic?
Yes, because it contains ferrite. A magnet will stick to it, unlike annealed 316, so a magnet test cannot tell you the grade. Use chemistry on the mill test report or a material verification method instead.
Is 2205 the same as 1.4462?
The two designations refer to the same grade family: the IMOA guide lists EN 1.4462 alongside UNS S32205 for 2205 plate (IMOA Practical Guidelines, 3rd ed., 2014). Name both on the drawing if your supplier works to EN stock.
Can I swap 2205 for 316 on an existing 316 drawing?
Not without review. The machining plan changes, and any press fit, thread or tolerance that was set for 316 behavior needs a check, because the higher strength, higher cutting forces and lower thermal expansion all affect the result. Quote it as a new part number or a revised drawing.
Does duplex 2205 need passivation like 316?
Stainless parts generally benefit from a clean, passive surface after machining, and duplex is no exception. Passivation is not among the finishes Saola currently lists, so state the requirement on the drawing, confirm who will apply it at drawing review, and see the guide on passivation of machined stainless parts.
Sources
- Practical Guidelines for the Fabrication of Duplex Stainless Steels, 3rd edition, International Molybdenum Association, 2014
- Duplex stainless steel, International Molybdenum Association, accessed 2026
- Selection of Duplex 2205 over Stainless steel 316L, report LJS 03-06, Material Selection Resources, October 26, 2006
- Duplex and super duplex steels, voestalpine Specialty Metals, accessed 2026