Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
ASTM A789: Super Duplex 2507 Tube
ASTM A789 is the standard specification for seamless and welded ferritic / austenitic stainless steel tubing for general service. Within A789, super duplex 2507 is registered as UNS S32750. The standard covers seamless, welded, heavily cold worked welded, and bead-rolled welded tubing for heat exchangers, condensers, instrument tubing, and umbilical tubing. The European parallel for tube is EN 10216-5 (seamless) for Werkstoff 1.4410.
TorqBolt supplies A789 UNS S32750 seamless tube and welded tube across diameters 6 mm to 273 mm OD with mill test certificates recording chemistry, mechanical properties, ferrite content, and hydrostatic / NDE evidence.
ASTM A789 Scope
A789 covers ferritic / austenitic (duplex and super duplex) stainless steel tubing for general service. Categories include seamless, as-welded, welded with cold work, and welded with bead removed. The standard governs chemistry, mechanical properties, heat treatment, dimensions, hydrostatic testing, NDE, and corrosion testing for tubular product up to 8 inch nominal diameter (273 mm OD).
ASTM A789 Chemistry for UNS S32750
| Element | Min % | Max % |
|---|---|---|
| Carbon (C) | (no min) | 0.030 |
| Chromium (Cr) | 24.0 | 26.0 |
| Nickel (Ni) | 6.0 | 8.0 |
| Molybdenum (Mo) | 3.0 | 5.0 |
| Nitrogen (N) | 0.24 | 0.32 |
| Manganese (Mn) | (no min) | 1.20 |
| Silicon (Si) | (no min) | 0.80 |
| Phosphorus (P) | (no min) | 0.035 |
| Sulfur (S) | (no min) | 0.020 |
| Copper (Cu) | (no min) | 0.50 max, residual, not intentional |
Mechanical Requirements
| Property | Minimum |
|---|---|
| Tensile strength | 795 MPa (116 ksi) |
| Yield strength (0.2 percent) | 550 MPa (80 ksi) |
| Elongation in 50 mm | 15 percent |
| Hardness | 32 HRC max |
Heat Treatment
Solution annealing at 1040 to 1100 degrees Celsius followed by rapid water quench. For welded tube, the post-weld solution anneal is critical to restore the ferrite / austenite balance disturbed by the welding heat input. Bead-rolled tube goes through the same annealing cycle after the bead is removed.
Required Tests
| Test | Method / Acceptance |
|---|---|
| Chemistry | Per ASTM E1086 family |
| Tensile | ASTM A370 |
| Hardness | HRC or HBW |
| Hydrostatic | To ASTM A999, per design pressure |
| NDE | Eddy current or ultrasonic per A1016 |
| Flaring or flattening | Per A1016 |
| Ferrite (S52) | ASTM E562 point count, 35 to 55 percent typical |
| Intermetallic (S57) | ASTM A923 Method A |
Tube Categories under A789
| Category | Description |
|---|---|
| Seamless | Hot-extruded or cold-pilgered, no weld seam |
| Welded | Strip rolled and longitudinally welded, as-welded condition |
| Welded + cold worked | Welded, then cold-finished for tighter tolerance |
| Welded + bead removed | Welded, internal weld bead removed for clean ID |
Applications for A789 2507 Tube
- Seawater heat exchanger tubing (cooler tubes, condenser tubes)
- Sulphuric and phosphoric acid service tubing
- Subsea umbilical tubing for hydraulic and chemical injection lines
- Offshore desalination feed and brine tubing
- Sour-service instrument tubing
- FPSO process tubing in chloride environments
Related Standards
- ASTM A790: pipe spec (larger sizes, pipe wall thickness)
- ASTM A479: bar spec
- ASTM A182 F53: forging spec
- ASTM A815: wrought fittings (WP-S32750)
- EN 10216-5: European seamless tube spec for Werkstoff 1.4410
- NORSOK M-630: MDS D57 (seamless tube)
- NACE MR0175 / ISO 15156-3: sour-service requirements
ASTM A789 Frequently Asked Questions
What does ASTM A789 cover for UNS S32750?
A789 specifies seamless and welded super duplex 2507 tubing for general service in solution-annealed condition. Includes seamless, welded, welded + cold worked, and welded + bead removed categories up to 8 inch (273 mm) OD.
What is the difference between A789 and A790?
A789 covers tube; A790 covers pipe. Tube is dimensioned by OD and wall; pipe is dimensioned by NPS and schedule. A789 covers OD up to 8 inch (273 mm); A790 covers full pipe size range. Same chemistry (UNS S32750), same heat treatment, different dimensional standards.
What heat treatment is applied to A789 welded tube?
Solution annealing at 1040 to 1100 degrees Celsius followed by rapid water quench, performed after welding. The post-weld anneal is essential to restore ferrite / austenite balance disturbed by welding heat input. As-welded tube without solution anneal is only admissible when the WPS qualification proves balanced microstructure.
What hydrostatic test pressure applies?
Per ASTM A999, the hydrostatic pressure is calculated from design stress and tube wall. Each tube is individually pressure tested before shipment. Eddy current or ultrasonic NDE is an admissible alternative to hydrostatic for thin-wall tube.
Is A789 acceptable for sour service?
Yes, when supplemented with NACE MR0175 / ISO 15156-3 requirements: 28 HRC max, 35 to 65 percent ferrite, qualified WPS for welded tube. Mill test certificate must record hardness and ferrite per the sour-service envelope.
Is A789 used for subsea umbilical tubing?
Yes. Super duplex 2507 per A789 is the dominant alloy for subsea hydraulic umbilical tubing where chloride and H2S exposure exceeds the carbon steel and 316L envelopes. Seamless tube is preferred for fatigue performance under repeated cyclic pressure.
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