What are the Different Grades of Stainless Steel Pipes?

Stainless steel pipes are available in various grades, and each grade serves a different temperature, pressure, and corrosion condition. Selecting the incorrect grade results in higher expenditures, either through premature failure or excessive expenditure on over-specified material.

This guide covers the five major families of stainless steel pipe grades, i.e., austenitic, ferritic, martensitic, duplex, and superduplex. It also covers the chemical composition, corrosion resistance, temperature restrictions, and appropriate applications for each grade.

5 Families of Stainless Steel Pipe Grades

Stainless steel pipe grades are classified into five families depending on their crystal structure and alloy concentration. These families include austenitic, ferritic, martensitic, duplex, and superduplex. Here’s a brief overview of each:

• Austenitic: It is the most common family, with 16-26% chromium and 6-22% nickel. Non-magnetic and highly corrosion-resistant.

• Ferritic: Contains 10.5–30% chromium with little or no nickel. Magnetic and lower cost.

• Martensitic: High hardness and moderate corrosion resistance. Used for valves and pump shafts.

• Duplex: A 50/50 mix of austenitic and ferritic phases. Double the yield strength of standard austenitic grades.

• Super Duplex: Higher alloy content than duplex. PREN above 40 for extreme corrosion environments.

Austenitic Stainless Steel Pipe Grades

Austenitic grades make up over 70% of all stainless steel pipe production worldwide. They belong to the 300 series and contain high chromium (16–26%) and nickel (6–22%) content.

1. SS 304 (UNS S30400)

SS 304 is the most preferred stainless steel grade for piping systems. It is contains of around 18% chromium and 8% nickel, and is also known as 18/8 stainless steel.

• Max service temperature: 870°C (1,598°F) for continuous use.

• Corrosion resistance: Excellent in air conditions and mild chemicals.

• Common applications: Food processing, water treatment, and architectural piping.

• ASTM standards: ASTM A312 (pipe), ASTM A213 (tube).

SS 304 does not resist chloride pitting well. Use it for general-purpose indoor service and mildly corrosive conditions.

2. SS 304L (UNS S30403)

SS 304L has the same composition as 304 but with carbon content limited to 0.03% maximum (versus 0.08% in standard 304).

The lower carbon prevents carbide precipitation during welding. This means 304L resists intergranular corrosion in the heat-affected zone after welding, making it the preferred choice for welded pipe fabrication.

3. SS 316 (UNS S31600)

SS 316 adds 2–3% molybdenum to the 304 base composition. This molybdenum addition gives 316 much better resistance to chloride pitting and crevice corrosion.

• PREN (Pitting Resistance Equivalent Number): ~23 (versus ~18 for 304)
• Max service temperature: 870°C (1,598°F) continuous
• Common applications: Chemical processing, marine environments, pharmaceutical piping

SS 316 is recommended where pipes are exposed to chlorides, seawater or acidic chemicals.

4. SS 316L (UNS S31603)

SS 316L is the low-carbon version of 316. Carbon is held at 0.03% maximum to prevent sensitisation during welding.

316L is the default choice for most industrial piping projects where welding is required and chloride exposure is expected. It combines good weldability with solid corrosion performance.

5. SS 321 (UNS S32100)

SS 321 is a titanium-stabilised grade. The titanium ties up carbon atoms, which prevents chromium carbide formation at temperatures between 425–870°C (797–1,598°F).

SS 321 is the preferred grade for applications including:

• Exhaust manifolds and headers
• Furnace parts exposed to thermal cycling
• Refinery piping that operates above 425°C for long periods

6. SS 347 (UNS S34700)

SS 347 uses niobium (columbium) stabilisation instead of titanium. Like 321, it resists intergranular corrosion at elevated temperatures.

The key advantage of 347 over 321 is better creep strength above 540°C (1,004°F). Power plants and refineries use 347 for superheater tubes and high-temperature reactor piping.

7. SS 904L (UNS N08904)

SS 904L is a super austenitic grade that contains 20% chromium, 25% nickel, 4.5% molybdenum, and 1.5% copper. This high alloy percentage results in a PREN of approximately 36.

904L resists:

• Sulfuric acid at concentrations up to 80%
• Phosphoric acid
• Chloride stress corrosion cracking (SCC)

Use 904L in harsh chemical situations where 316L does not provide sufficient corrosion resistance and nickel alloys are too expensive.

Ferritic Stainless Steel Pipe Grades

Ferritic grades consist of between 10.5 and 30% chromium and a small percentage of nickel. They are magnetic, less costly, and resist stress corrosion cracking better than austenitic grades. 409 and 430 are two commonly used ferritic grades for piping.

These grades work well for automotive exhaust systems, heat exchangers, and indoor architectural applications. These grades are magnetic and generally lower in cost than austenitic grades.

Martensitic Stainless Steel Pipe Grades

Martensitic grades like 410 and 420 offer high hardness after heat treatment. They contain 11.5–18% chromium and up to 1.2% carbon.

Martensitic stainless steels are used for:

• Valve stems and pump shafts
• Turbine blades
• Cutlery and surgical instruments

These grades are rarely used for pipe runs. Their weldability is poor, and they need pre-heat and post-weld heat treatment.

Duplex Stainless Steel Pipe Grades

Duplex stainless steel pipes have a 50/50 microstructure of austenite and ferrite phases. This dual-phase structure gives them roughly twice the yield strength of 304 or 316,  while maintaining good corrosion resistance.

1. Duplex 2205 (UNS S31803 / S32205)

Duplex 2205 is the most used duplex grade, covering about 80% of all duplex applications.

• Composition: 22% Cr, 5% Ni, 3% Mo, 0.15% N
• PREN: ~35
• Yield strength: 450 MPa (65 ksi) minimum, roughly double that of 316L
• Applications: Offshore platforms, desalination plants, chemical tankers, and pulp &paper industries.

Duplex 2205 handles chloride environments, moderate acids, and temperatures up to 315°C (600°F).

2. Duplex 2304 (UNS S32304)

Duplex 2304 is a lean duplex grade with lower molybdenum content. It costs less than 2205 and offers similar strength but with a PREN of ~25.

Use 2304 when you need duplex strength, but the corrosion conditions are mild.

Super Duplex Stainless Steel Pipe Grades

Super duplex pipes have a PREN of 40 or above. They combine very high strength with extreme corrosion resistance for the most demanding environments.

1. Super Duplex 2507 (UNS S32750)

• Composition: 25% Cr, 7% Ni, 4% Mo, 0.28% N

• PREN: ~43

• Yield strength: 550 MPa (80 ksi) minimum

• Applications: Subsea flowlines, sour gas processing, hot seawater systems

2. Super Duplex 2760 (UNS S32760)

• Composition: 25% Cr, 7% Ni, 3.5% Mo, 0.7% Cu, 0.7% W.

• PREN: ~41 (calculated with Mo + 0.5×W) to show awareness of the W contribution.

• Applications: Offshore risers, umbilicals, and harsh chloride environments. We manufacture both duplex and super duplex seamless pipes that meet ASTM A789 and A790 standards.

How to Choose the Right Stainless Steel Pipe Grade?

Selecting the correct grade comes down to 4 factors:

• Corrosion environment: Identify the chemicals present, operating temperature, and chloride exposure the pipe will face. Higher PREN values indicate better resistance to pitting corrosion, especially in chloride-rich environments.

• Operating temperature: Standard austenitic grades handle up to 870°C. Stabilised grades (321, 347) are better above 425°C. Duplex grades top out at 315°C.

• Mechanical strength needs: Duplex and super duplex grades provide twice the yield strength of austenitic grades, allowing for thinner walls and less weight.

• Budget: 304 is the cheapest austenitic option. 316L adds 15–20% more cost. Duplex 2205 costs about 30% more than 316L. Super duplex adds another 20–30%. As the cost differentials are indicative and fluctuate with nickel and molybdenum market prices

Stainless Steel Pipe Grade Comparison Table

This table compares 8 commonly used stainless steel pipe grades by composition, PREN, yield strength, and typical use.

Conclusion

Stainless steel pipe grades range from basic 304 for general use to super duplex 2507 for the most extreme offshore circumstances. The choice is based on corrosion exposure, temperature, strength requirements, and budget.
Start with 304 or 316L for standard industrial work. Move to duplex 2205 when you need higher strength and better pitting resistance. Super duplex 2507 is appropriate for subsea and sour gas service for subsea and sour gas service. We manufacture all these grades as seamless pipes and tubes. Contact our technical team for grade-specific availability, dimensional specifications, and pricing.