ASTM A789: Duplex & Super-Duplex Stainless Steel Tubing Specification
ASTM A789/A789M carries the formal title Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service, and ASTM International publishes it. The standard governs small-diameter duplex stainless steel tubing in grades like S31803, S32205, S32750 and S32760, setting requirements for chemistry, mechanical properties, dimensions, and the tests a tube has to pass. "Ferritic/austenitic" is simply the standard's term for duplex: a roughly 50/50 two-phase microstructure valued for its resistance to chloride stress-corrosion cracking (SCC) and for its strength. Crestflo, a US-serving manufacturer of duplex and super-duplex instrumentation and process tubing, can supply product ordered to ASTM A789.
Also known as: ASTM A789/A789M, ASME SA-789 and related designations
Engineers and buyers specify this standard under several names. It's written as ASTM A789/A789M, a dual document carrying both inch-pound and SI (metric) requirements, and the current edition carries the designation A789/A789M-24. When adopted into the ASME Boiler & Pressure Vessel Code, it's cited as ASME SA-789 (also written SA-789 or SA789), with the same technical requirements applied in a code context. People also call it the "A789 tubing spec," the "ASTM A789 duplex tubing standard," or simply "ferritic/austenitic stainless steel tubing."
What ASTM A789 covers: scope and general service
A789 sets the requirements for seamless and welded duplex stainless steel tubing meant for general service, a broad category covering heat exchangers, condensers, feedwater heaters, and seawater or chloride-bearing process lines. Welded tubing under A789 comes without added filler metal. The duplex grades in scope combine austenitic toughness with ferritic strength and pitting resistance, which is why the standard gets cited so often wherever 304L or 316L tubing would risk chloride stress-corrosion cracking. Its companion standard, ASTM A790, covers duplex pipe. The austenitic tubing specs ASTM A213 and ASTM A269, by contrast, cover different alloy families entirely.
Grades in ASTM A789: duplex and super-duplex UNS numbers
The standard groups a family of duplex and super-duplex grades under UNS number designations. Below are the headline grades along with their common trade names; the complete grade list appears in the current published edition.
| UNS No. | Common / trade name | Family | Instrumentation form |
|---|---|---|---|
| S32205 / S31803 | 2205 | Duplex | Duplex 2205 tubing |
| S32750 | 2507 (super-duplex) | Super-duplex | Super-Duplex 2507 tubing |
| S32760 | Zeron 100 | Super-duplex | Super-Duplex 2507 tubing |
| S32304 | 2304 (lean duplex) | Lean duplex | On request |
| S32550 | 255 (Ferralium) | Super-duplex | On request |
Crestflo covers the full alloy metallurgy, composition and product-form detail on separate pages. See the Duplex 2205 material page for 2205, and the Super-Duplex 2507 material page for 2507.
ASTM A789 chemical composition and PREN by grade
Duplex performance comes down to a balanced mix of chromium, molybdenum and nitrogen. The nominal composition ranges below are published values for the principal A789 grades; the pitting resistance equivalent number (PREN = Cr + 3.3×Mo + 16×N) gets derived from them. Values follow the applicable standard and can be adjusted to requirement. Confirm exact limits against the heat certificate.
| Grade (UNS) | C max | Cr % | Ni % | Mo % | N % | PREN (typ.) |
|---|---|---|---|---|---|---|
| 2205 (S32205) | 0.030 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 | 0.14–0.20 | ~35 |
| 2205 (S31803) | 0.030 | 21.0–23.0 | 4.5–6.5 | 2.5–3.5 | 0.08–0.20 | ~34 |
| 2507 (S32750) | 0.030 | 24.0–26.0 | 6.0–8.0 | 3.0–5.0 | 0.24–0.32 | ~42 |
| Zeron 100 (S32760) | 0.030 | 24.0–26.0 | 6.0–8.0 | 3.0–4.0 | 0.20–0.30 | ~40 |
| 2304 (S32304) | 0.030 | 21.5–24.5 | 3.0–5.5 | 0.05–0.60 | 0.05–0.20 | ~25 |
ASTM A789 mechanical properties: tensile, yield and hardness
A789 lays out minimum tensile strength, minimum yield strength, minimum elongation and a maximum hardness for each grade. Below are the published minima for the two most commonly specified grades (values per the applicable standard; adjustable to requirement).
| Grade | Tensile min | Yield 0.2% min | Elongation min | Hardness max |
|---|---|---|---|---|
| 2205 (S31803/S32205) | 90 ksi (620 MPa) | 65 ksi (450 MPa) | 25% | 30 HRC / 290 HBW |
| 2507 (S32750) | 116 ksi (795 MPa) | 80 ksi (550 MPa) | 15% | 32 HRC / 310 HBW |
Seamless vs welded tubing under ASTM A789
Duplex tubing under this standard comes in two forms: seamless and welded. Seamless tubing starts as a hollow that's cold-worked into shape, with no weld seam at all, and it tends to get the nod for the highest-integrity or higher-pressure jobs. Welded tubing is different: it's formed and autogenously welded without added filler metal, then solution annealed. That route makes more economic sense for larger quantities and thinner walls. Either way, both types ship solution-annealed and pickled, which restores the duplex phase balance and corrosion resistance. Take a look at seamless duplex tubing and welded duplex tubing from Crestflo.
ASTM A789 dimensions, wall thickness and tolerances
A789 sets outside diameter and wall thickness with tolerances per the standard, and buyers can order on an average-wall or minimum-wall basis. It's built for small-diameter tubing, which makes it the go-to spec for instrumentation tubing and heat-exchanger tube. OD and wall dimensions follow the standard tube tables but can be customized to requirement, and Crestflo offers both imperial and metric sizes.
ASTM A789 testing, NDT and corrosion validation
Every tube has to clear either a hydrostatic test or a nondestructive electric (eddy-current) test, along with mechanical and process testing. When specified, supplementary corrosion tests are required too.
| Test | Basis | Purpose |
|---|---|---|
| Hydrostatic OR eddy-current | Required (one of two) | Pressure integrity / flaw detection |
| Flattening | Required | Ductility and weld soundness |
| Flange / flaring | Required | Formability at the tube end |
| Hardness | Required | Confirms proper annealing |
| Tension | Required | Verifies strength minima |
| ASTM A923 / ASTM G48 | Supplementary | Intermetallic-phase and pitting resistance |
Crestflo backs this up with in-house NDT, hydraulic proof and burst testing, destructive testing at ISO/IEC 17025-accredited labs, and PMI on material. Every tubing shipment includes an EN 10204 3.1 material test certificate as standard, with 3.2 available on request, plus a heat/lot number stamped on each part, see EN 10204 material test certificates and material traceability. Third-party inspection can be arranged on request.
ASTM A789 vs A790 (and vs A269/A213)
The most common point of confusion is A789 versus A790. They're sibling duplex standards, and what separates them is product form.
| Standard | Product form | Material family | Typical use |
|---|---|---|---|
| ASTM A789 | Tubing (small diameter) | Duplex / super-duplex | Heat exchangers, instrumentation, condensers |
| ASTM A790 | Pipe | Duplex / super-duplex | Fluid and gas transport |
| ASTM A269 | Tubing | Austenitic (304/316) | General-service instrumentation tube |
| ASTM A213 | Tubing | Austenitic | Boiler, superheater, heat-exchanger tube |
For pipe, the nearest ASTM A789 equivalent is A790. No single international standard lines up one-to-one with it, though EN and JIS tube standards do use the same UNS duplex grades. Put simply: A789 covers duplex tubing, A790 covers duplex pipe, and A269/A213 cover austenitic tubing. Duplex tubing intended for sour service also has to meet NACE MR0175 / ISO 15156, a standard Crestflo's own reference page walks through in detail. North Sea work is a different animal: there, material data-sheet conformance falls under NORSOK M-630.
ASME SA-789 relationship
SA-789 is ASTM A789 as it was adopted into the ASME Boiler & Pressure Vessel Code. The "SA" prefix marks that adoption; chemistry, mechanical properties and test requirements all match the ASTM document, just applied inside the BPVC framework. Take a grade like SA-789 S31803: it's the same material as A789 S31803, only specified for code work.
Where ASTM A789 duplex tubing is used
Duplex and super-duplex A789 tubing handles the tough jobs: chloride exposure, high pressure, seawater cooling, desalination, offshore and subsea process lines, heat exchangers, condensers, chemical and petrochemical instrument lines, and pulp-and-paper bleaching circuits. What makes it a swap-in for 316L in brackish, marine and high-chloride settings comes down to one thing: its resistance to stress-corrosion cracking. Browse duplex stainless instrumentation and process tubing and alloy tubing from Crestflo.
Source ASTM A789 duplex tubing from Crestflo: request a quote
Crestflo supplies Duplex 2205 and Super-Duplex 2507 instrumentation and process tubing to ASTM A789, in both imperial and metric sizes, and serves customers across the US as a supplier and manufacturer. Standard items ship from ready stock; specials are made to order, with lead times of 6–8 weeks. Pricing for ASTM A789 material is quoted against your grade, size and quantity, and it stays cost-competitive even after US duties are factored in. The material itself is of Indian origin. US or European melt is available on request, and full traceability is provided on every order. Crestflo holds ISO 9001, 14001 and 45001 certification, along with PED certification. Every order ships with EN 10204 3.1 certification (3.2 available on request), heat-number marking and PMI.
Request a quote for A789 duplex tubing, request a sample, or take a look at Crestflo's distributor program.
Why Crestflo for duplex tubing
Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house with a Middle-East delivery track record. That heritage backs a new manufacturing brand. Buyers get a US-serving source with clear traceability where offshore mills give none: EN 10204 3.1/3.2 certificates, heat-number marking on every part, in-house NDT and 17025-accredited destructive testing, small MOQ, private-label capability, and a lead time of 6-8 weeks against the 20-plus weeks common with the majors. Learn more at Why Crestflo.
Frequently asked questions about ASTM A789
What is ASTM A789?
ASTM A789/A789M sets the standard for seamless and welded ferritic/austenitic (duplex) stainless steel tubing used in general service. It covers grades such as S31803, 2205, S32750 and S32760, along with their chemistry, mechanical properties and the tests required to verify them.
What grades does ASTM A789 cover?
The 2205 duplex grade covers S31803 and S32205, plus S32304 (lean duplex, 2304), S32750 (2507) and S32760 (Zeron 100). Additional duplex and super-duplex UNS grades are included per the current edition.
What is the difference between ASTM A789 and A790?
A789 covers duplex stainless tubing: small diameter, meant for heat exchangers and instrumentation work. A790 covers duplex pipe, used for moving fluids and gases. The alloy families match. What differs is the product form and the dimensional tables.
Is ASTM A789 the same as ASME SA-789?
SA-789 is ASTM A789 as adopted into the ASME Boiler & Pressure Vessel Code. The technical requirements don't change; the SA designation just marks its use in a code context.
Does ASTM A789 cover both seamless and welded tubing?
Yes. Both seamless and welded tubing are allowed. Welded tubing is made without added filler metal and gets supplied solution annealed.
What tests does ASTM A789 require?
A hydrostatic test or a nondestructive eddy-current test is required, along with flattening, flange/flaring, hardness and tension tests. When specified, supplementary intergranular and pitting-corrosion tests are added, including ASTM A923 and G48.
Why choose duplex tubing over 304 or 316?
Duplex grades hold up far better against chloride stress-corrosion cracking, and their yield strength runs roughly double that of 304L/316L, so you can go thinner on walls in chloride-rich or seawater service. See how 2205 stacks up against 2507 at 2205 vs 2507.
Can Crestflo supply ASTM A789 duplex tubing?
Crestflo supplies Duplex 2205 and Super-Duplex 2507 tubing, and it can be ordered to ASTM A789. Certification comes with EN 10204 3.1 (3.2 on request), plus heat-number traceability and PMI. Request a quote.
Is ASTM A789 the same as A7?
No. A7 is an obsolete structural-steel specification. It has nothing to do with A789, which covers duplex stainless steel tubing.
Where can I get the official ASTM A789 PDF or document?
The official ASTM A789 PDF comes from ASTM International, which publishes and sells it directly. Crestflo points to A789 when discussing material supply, but it doesn't hand out copies of the document itself.
Related standards and materials
- ASTM A790, duplex stainless pipe
- ASTM A269, austenitic stainless tubing
- ASTM A213, austenitic boiler/heat-exchanger tubing
- ASTM A479, stainless bar and shapes
- NACE MR0175 / ISO 15156, sour service
- NORSOK M-630, duplex material data sheets
- EN 10204, material test certificates
- Duplex 2205 material · Super-Duplex 2507 material
- Duplex vs. Super-duplex · All standards