UNS S32750 vs UNS S32760 Super Duplex: Chemistry and Grade Selection

Written by: Emma, Technical Sales Engineer  |  Reviewed by: Ethan, Materials Engineer  |  Updated: August 2026

UNS S32750 vs S32760 is a comparison that comes up repeatedly in offshore, marine, and oil and gas projects. Both grades are super duplex stainless steels, both are known under trade names (2507 and Zeron 100 respectively), and both deliver very high strength and chloride corrosion resistance. Yet they are not the same material, and treating them as freely interchangeable can create procurement and performance risk.

This article explains the chemistry differences between S32750 and S32760, how those differences affect corrosion resistance, and how to decide between the two grades — or whether a substitution requires engineering approval. It is written for materials engineers, offshore and oil and gas equipment engineers, fabricators, and B2B buyers.

1. Direct Answer

S32750 and S32760 are both super duplex stainless steels, and their performance is closely matched in many environments. However, they are not identical grades. Their chemistry, PREN, mechanical properties, applicable standards, and qualification requirements can all differ, and those differences matter in specific service conditions.

The practical conclusion is that neither grade should be substituted for the other purely on the basis of "both are super duplex." Any substitution must be reviewed against the project specification, the service environment, the design code, and the welding and certification requirements.

2. Quick Comparison

3. Chemistry Differences

The two grades share a similar base of chromium, nickel, molybdenum, and nitrogen, but they diverge in a few important ways. The following explains what each element contributes, rather than simply listing percentages, because the exact composition must always be taken from the applicable ASTM/EN standard or reliable material data, and product specifications can differ.

• Chromium (Cr): Both grades carry a high chromium level, roughly in the mid-20% range. Chromium is the backbone of passivity and general corrosion resistance.
• Molybdenum (Mo): Molybdenum is a strong contributor to pitting and crevice corrosion resistance. S32750 typically has a somewhat higher molybdenum content than S32760.
• Nitrogen (N): Nitrogen strengthens the alloy and improves pitting resistance (it appears in the PREN formula). Both grades use a significant nitrogen addition.
• Nickel (Ni): Nickel stabilizes austenite and helps maintain phase balance. Both grades carry a broadly similar nickel level.
• Tungsten (W): This is a key differentiator. S32760 includes a deliberate tungsten addition, which is intended to enhance resistance to localized corrosion — particularly crevice corrosion — in certain aggressive environments. Tungsten is generally not a deliberate addition in S32750.
• Copper (Cu): S32760 also includes a deliberate copper addition, which is intended to improve resistance in certain acidic and reducing conditions. Copper is generally not a deliberate addition in S32750.

The practical meaning is that S32750 leans on a higher molybdenum content, while S32760 uses tungsten and copper to tune its performance for specific aggressive services. These are design choices, not evidence that one grade is universally superior.

4. PREN and Corrosion Resistance

A common way to rank pitting resistance is the PREN (Pitting Resistance Equivalent Number):

PREN = %Cr + 3.3 × %Mo + 16 × %N

PREN is useful for alloy-level comparison, but it is not an actual service limit. Both S32750 and S32760 sit in the super duplex range with a PREN of 40 or higher. On the standard formula, S32750 often shows a marginally higher value because of its higher molybdenum. However, the standard PREN formula does not include tungsten, so it does not fully capture the localized corrosion contribution that S32760’s tungsten addition is intended to provide. This is one reason why PREN should never be used alone to declare one grade "better."

When comparing corrosion resistance, the relevant mechanisms should be considered separately:

• Pitting: Both grades offer very high pitting resistance in chloride service.
• Crevice corrosion: Both offer high crevice corrosion resistance; S32760’s tungsten addition is specifically intended to help in this mode, but real performance also depends on crevice geometry and temperature.
• Chloride SCC: Both grades, as duplex materials, resist chloride stress corrosion cracking well.
• Seawater / chloride service: Both are widely used in seawater and chloride-bearing environments.

Temperature, chloride level, oxygen, flow, crevice geometry, surface condition, and welding all affect actual performance as much as — and often more than — the alloy chemistry itself.

5. S32750 vs S32760 in Seawater

Both grades are well suited to seawater, desalination, offshore, oil and gas, and chloride-bearing environments. They are both used in seawater piping, heat exchangers, pumps, valves, and structural components where high chloride resistance and high strength are required.

It would be wrong to state flatly that "S32760 is better" or "S32750 is better" in seawater. The right grade depends on the specific conditions — temperature, crevice geometry, flow, fouling, and the presence of other aggressive species. Where a project specification calls for one grade, the other should not be substituted without an engineering review.

No fixed chloride ppm, temperature limit, CPT/CCT value, or corrosion rate is quoted here, because those are not universal. Where experimental data is used, the test method and conditions must be stated, and laboratory results must not be read as a direct field service limit.

6. Strength and Design

Both S32750 and S32760 are high-strength grades with yield and tensile strength far above conventional austenitic stainless steels, and with usable elongation and toughness.

The design implication is that higher strength can enable lighter or thinner components — but this does not mean wall thickness can be reduced in direct proportion to the strength ratio. Actual design must follow the governing design code and account for pressure, temperature, fatigue, buckling, corrosion allowance, and weld efficiency. Strength is only one input into a safe design.

7. Standards, Welding and Certification

The UNS designation is a chemical designation, not a complete procurement specification. To buy either grade correctly, the full specification chain matters:

• ASTM / ASME / EN: The applicable product standard for the specific product form (plate, pipe, tube, fitting, forging);
• UNS designation: Stated explicitly as UNS S32750 or UNS S32760;
• Product form: The correct form-specific standard;
• Heat treatment: Solution annealing requirements;
• MTC: A material test certificate confirming chemistry and mechanical properties;
• Heat-number traceability: Traceability of material back to its heat;
• WPS/PQR: Qualified welding procedures and procedure qualification records;
• Filler qualification: Filler metal matched to the specific grade and process.

S32750 and S32760 cannot be swapped without engineering approval, because welding procedure qualification, filler selection, and certification may not carry over automatically from one grade to the other.

8. When to Choose S32750 or S32760

In many projects the choice is driven by the project specification and availability rather than by a narrow performance edge. In general:

• S32750 is a widely used, well-documented super duplex grade, frequently specified for seawater, oil and gas, and chemical service where high molybdenum content is the reference point.
• S32760 is often specified where its tungsten and copper additions are valued — for example, in certain aggressive offshore, marine, or acidic services — and where the project specification or end-user preference calls for it.

The final decision should be based on the project specification, the service environment, the corrosion requirements, the design code, the welding qualification, material availability, and the certification requirements — not on a single number such as PREN.

9. How to Specify in an RFQ

To avoid ambiguity when buying either grade, include at minimum:

• UNS grade: UNS S32750 or UNS S32760, stated explicitly;
• ASTM/EN product standard: The applicable standard for the product form;
• Product form: Plate, pipe, tube, fitting, or forging;
• Dimensions: Size, thickness, and length where applicable;
• Heat treatment: Solution annealing requirements;
• Mechanical requirements: Yield, tensile, and elongation;
• Service medium: What the equipment will contain or process;
• Design temperature: Minimum and maximum operating temperature;
• Chloride conditions: Chloride level where relevant;
• NDE: Non-destructive examination requirements;
• Corrosion testing: Where required by the project;
• WPS/PQR: Qualified welding procedures and qualification records;
• MTC: Requirement for a material test certificate;
• Heat-number traceability: Material traceable to its heat number.

10. Common Purchasing Mistakes

• Assuming S32750 and S32760 are identical;
• Looking only at PREN and ignoring everything else;
• Treating CPT or CCT as a service limit;
• Ignoring the product standard and product form;
• Ignoring welding qualification when changing grades;
• Reducing wall thickness directly from the strength ratio;
• Substituting grades without engineering approval;
• Checking only the grade name without verifying the MTC.

FAQ

Q1: What is the difference between S32750 and S32760?
Both are super duplex grades with similar chromium, nickel, and nitrogen levels. The main difference is that S32750 typically has higher molybdenum, while S32760 includes deliberate tungsten and copper additions intended to enhance localized corrosion resistance and performance in certain acidic conditions.

Q2: Are S32750 and S32760 both super duplex stainless steels?
Yes. Both are super duplex stainless steels with a PREN of 40 or higher, high strength, and high chloride corrosion resistance.

Q3: Is S32760 more corrosion resistant than S32750?
Not universally. S32760’s tungsten and copper additions are intended to help in specific aggressive conditions, while S32750 relies on higher molybdenum. Which performs better depends on the actual environment, and neither grade is "better" in all cases.

Q4: Which has the higher PREN?
On the standard PREN formula (%Cr + 3.3%Mo + 16%N), S32750 often shows a marginally higher value because of its higher molybdenum. However, the standard formula does not include tungsten, so it does not fully reflect S32760’s design. Both are in the super duplex range.

Q5: Can both grades be used in seawater?
Yes. Both S32750 and S32760 are widely used in seawater, desalination, and offshore applications where high chloride resistance and high strength are required.

Q6: Can S32750 replace S32760?
Not automatically. A substitution requires review against the project specification, service environment, design code, welding qualification, and certification requirements. They should not be treated as freely interchangeable.

Q7: Can S32760 replace S32750?
The same caution applies. S32760 should not be substituted for S32750 without engineering approval, because welding, filler, and certification requirements may differ.

Q8: Are S32750 and S32760 interchangeable for welding?
No. Welding procedure qualification and filler selection are specific to the grade and process, and a procedure qualified for one grade does not automatically transfer to the other.

Q9: Which grade is better for chloride service?
There is no universal answer. Both offer very high chloride resistance. The choice depends on temperature, crevice geometry, flow, surface condition, and the specific service environment, not on a single alloy ranking.

Q10: What should be included in an S32750 or S32760 RFQ?
Include the UNS grade, ASTM/EN product standard, product form, dimensions, heat treatment, mechanical requirements, service medium, design temperature, chloride conditions, NDE, corrosion testing where required, WPS/PQR, MTC, and heat-number traceability.

Related Reading

• UNS S32750 Super Duplex Welding: Filler Metal, Heat Input and Testing
• UNS S32750 Super Duplex in Seawater: Chloride and Crevice Corrosion Limits
• UNS S32205 Duplex Stainless Steel Welding: Heat Input and Phase Balance
• Super Duplex Grade Selection: A Practical Overview