ASTM A789 / A789M covers the requirements for seamless and welded duplex stainless steel tubes for general corrosion-resistant service, with particular emphasis on resistance to stress corrosion cracking. This product combines the excellent toughness of austenitic stainless steel with the high strength of ferritic stainless steel, while offering superior resistance to chloride-induced pitting and crevice corrosion.

This product covers common grades including UNS S31803, S32205 (2205 duplex), as well as UNS S32750 and S32760 (super duplex). Compared to traditional nickel-based alloys, duplex stainless steel can achieve the same design strength with thinner wall thicknesses, providing high cost and performance advantages in harsh environments.

Related Standard Note: ASTM A790 is another standard specification for duplex steel pipe, typically covering larger diameters, while ASTM A789 focuses on smaller-diameter tubes for heat exchangers, boilers, and general piping systems.

• Chemical Composition: Cr 21–23% / 22–23%, Mo 2.5–3.5% / 3.0–3.5%, Ni 4.5–6.5%, N 0.08–0.20%

• Characteristics: Typical duplex stainless steel offering excellent strength and resistance to chloride stress corrosion cracking. S32205 is often supplied as a dual grade with S31803.

• Equivalent Grades: EN 1.4462, AISI 2205

• Applications: Chemical vessels, piping, heat exchangers, seawater systems

• Chemical Composition: Cr 24–26%, Mo 3–5%, Ni 6–8%, N 0.24–0.32%

• Characteristics: Super duplex stainless steel with extremely high pitting and crevice corrosion resistance. PREn (Pitting Resistance Equivalent Number) typically >40.

• Equivalent Grades: EN 1.4410, SAF 2507, F53

• Applications: Marine engineering, desalination, oil & gas extraction, sour media

• Chemical Composition: Cr 24–26%, Mo 3–4%, Ni 6–8%, N 0.20–0.30%, with Cu and W additions

• Characteristics: Similar to S32750, with additional copper and tungsten to enhance corrosion resistance in specific environments.

• Equivalent Grades: EN 1.4501, F55, Zeron 100

• Applications: Subsea pipelines, seawater pump shafts, chemical processing equipment

Important Note: Duplex stainless steels are susceptible to embrittlement due to intermetallic phase precipitation if used for prolonged periods at elevated temperatures. Prolonged service in the range of 300–950°C should be avoided.

In accordance with ASTM A789 and the general requirements of A1016, each tube shall be subjected to the following tests:

• 100% Eddy Current Test (ET)

• 100% Hydrostatic Test

• Tension test

• Flaring test (for seamless tubes)

• Flange test (for welded tubes)

• Hardness test

• Reverse flattening test

• Heat analysis (per heat)

• Product analysis (upon request)

1. What is the difference between ASTM A789 and ASTM A790?

• A789: Covers seamless and welded small-diameter tubes, typically used for heat exchangers, boilers, and general piping.

• A790: Covers seamless and welded large-diameter pipes, typically used for transmission lines, risers, and larger systems. Both standards have essentially the same material property requirements.

2. How do I choose between S31803 and S32205?
The chemical compositions are similar, but S32205 has tighter requirements for molybdenum and nitrogen, providing higher corrosion resistance and strength. Many suppliers provide material certified to both grades (dual certified). In practice, S32205 fully meets the requirements of S31803.

3. What are super duplex grades S32750 / S32760 primarily used for?
These grades are used in highly corrosive environments, including:

• High-chloride seawater systems

• Sour oil and gas fields (containing H₂S / CO₂)

• High-temperature, high-chloride chemical media

• Subsea pipelines and deep-water equipment

4. Can duplex stainless steel be used at low temperatures?
Yes. Duplex stainless steels maintain good toughness at low temperatures, though slightly lower than austenitic grades. The typical minimum service temperature is -40°C. For lower temperatures, impact testing is recommended.

5. What should be considered when welding duplex stainless steel tubes?

• Control heat input (typically 0.5–2.5 kJ/mm)

• Maintain interpass temperature ≤150°C

• Use filler metals with matching nitrogen content (e.g., 2209, 2509 wire)

• Post-weld heat treatment is generally not recommended unless required to restore phase balance (in which case, solution annealing is used)

6. What test certificates can be provided?
Standard EN 10204 3.1 manufacturer's certificate is provided. EN 10204 3.2 (third-party witnessed) certificates or NACE MR0175 / ISO 15156 compliance statements can be arranged upon request.

7. Can small quantities or trial orders be supplied?
Yes, depending on size and grade. Please provide detailed specifications for the evaluation of stock availability and minimum order quantity.

The following should be specified at the time of order:

1. Grade (e.g., UNS S32205 / S32750)

2. Size (OD * WT, in mm or inches)

3. Length (fixed length or random length)

4. Quantity (meters, pieces, or metric tons)

5. Manufacturing Type (Seamless / Welded)

6. Surface Condition (Annealed & Pickled / Bright Annealed / Polished)

7. Testing Requirements (Eddy Current / Hydrostatic / Ultrasonic / Third-party inspection)

8. Certificate Required (EN 10204 3.1 / 3.2)

• Packaging: Woven fabric bundles, plywood wooden cases, or standard seaworthy export packing

• Protection: Plastic caps on ends (if applicable), moisture-proof lining inside

• Marking: Grade, size, heat number, and standard clearly labeled

• Port of Loading: Typically, major Chinese ports (e.g., Qingdao, Shanghai), subject to agreement