ASTM A790: Duplex & Super-Duplex Stainless Steel Pipe Specification
ASTM A790/A790M is the Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Pipe, published by ASTM International. It governs duplex and super-duplex stainless steel pipe, grades such as S31803, S32205, S32750 and S32760, covering chemistry, mechanical properties, dimensions and the tests each pipe must pass. "Ferritic/austenitic" is the standard's own name for duplex: a roughly 50/50 two-phase microstructure valued for chloride stress-corrosion cracking (SCC) resistance and high strength. A790 covers pipe; its companion, ASTM A789, covers duplex tubing, and that tube specification is the one Crestflo builds duplex and super-duplex instrumentation tubing to.
Also known as: ASTM A790/A790M, ASME SA-790 and related designations
Engineers and buyers refer to this standard by several names. On paper, it's ASTM A790/A790M, a dual document that carries both inch-pound and SI (metric) requirements. Adopt it into the ASME Boiler & Pressure Vessel Code, though, and the citation changes to ASME SA-790 (sometimes written SA-790 or SA790), with identical technical requirements applied in a code context. People also call it the "A790 pipe spec," the "ASTM A790 duplex pipe standard," the "super-duplex pipe specification," or simply the "ferritic/austenitic stainless steel pipe" standard.
What ASTM A790 covers: scope and duplex pipe
A790 sets out the requirements for seamless and welded duplex stainless steel pipe. Under A790, welded pipe carries no added filler metal; when filler metal is used to weld duplex pipe, that falls under ASTM A928 instead. The duplex grades in scope pair austenitic toughness with ferritic strength and solid resistance to pitting, which is why A790 gets cited whenever 304L or 316L pipe would be at risk of chloride stress-corrosion cracking. Crestflo keeps the scope tight here: A790 covers duplex pipe, full stop. It isn't ASTM A312, which covers austenitic pipe, not ASTM A789, which covers duplex tube, and not ASTM A928, duplex pipe welded with filler metal.
Grades in ASTM A790: duplex and super-duplex UNS numbers
The standard lists a family of duplex and super-duplex grades by UNS number. Below are the headline grades, along with their common trade and Werkstoff designations; the full grade list follows the current published edition.
| UNS No. | Common / trade name | Werkstoff | Family | Alloy detail |
|---|---|---|---|---|
| S32205 / S31803 | 2205 (F51) | 1.4462 | Duplex | Duplex 2205 material |
| S32750 | 2507 / super-duplex (F53) | 1.4410 | Super-duplex | Super-Duplex 2507 material |
| S32760 | Zeron 100 (F55) | 1.4501 | Super-duplex | Super-Duplex 2507 material |
| S32304 | 2304 (lean duplex) | 1.4362 | Lean duplex | On request |
| S32550 | 255 (Ferralium) | 1.4507 | Super-duplex | On request |
Additional ferritic/austenitic grades appear in the current edition, including S32520, S32906, S39274, S31500, S31200, S31260, S32003, S32101 and S32950. Zeron 100® and Ferralium® are trade names belonging to their respective grade owners; they're used here only to identify the UNS material.
ASTM A790 chemical composition and PREN by grade
Duplex performance rests on a balanced mix of chromium, molybdenum and nitrogen. The nominal composition ranges below are published figures for the principal A790 grades, and the pitting resistance equivalent number (PREN = Cr + 3.3×Mo + 16×N) is calculated from them. Values follow the applicable standard and can be adjusted to requirement, so exact limits should be confirmed 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 A790 mechanical properties: tensile, yield and hardness
A790 sets minimum tensile and yield strength, minimum elongation and a maximum hardness for each grade. The published minima for the two most-specified grades appear below (values per the applicable standard; customizable to requirement). Duplex grades deliver roughly double the yield of austenitic 304L/316L. The hardness ceiling is what ties the material to sour-service acceptance.
| 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 pipe under ASTM A790 (no filler metal)
The standard permits both seamless and welded duplex pipe. Seamless pipe is extruded or pierced with no weld seam, and it's often specified for the highest-integrity or higher-pressure service. Welded pipe gets formed and autogenously welded without added filler metal, then solution annealed. Both routes come out solution-annealed and quenched, which restores the duplex phase balance and corrosion resistance. Duplex pipe made with added filler metal falls outside A790. It's covered by ASTM A928 instead, a common point of confusion when a project references "welded duplex pipe."
ASTM A790 dimensions, schedules and tolerances
A790 sets the outside diameter, wall thickness and length, all within tolerances laid out in the standard. Nominal pipe sizes and schedules, Sch 10S, 40S, 80S and heavier, track the dimensional tables in ASME B36.19M (stainless) and B36.10M. Dimensions follow whichever standard applies, and they can be customized to a customer's requirement; both imperial and metric sizes are recognized. Small-diameter duplex product measured on an OD/wall basis rather than a nominal-pipe basis falls under a different rule, though. There, the companion tube standard ASTM A789 takes over, and Crestflo works to that spec accordingly.
ASTM A790 testing, NDT and corrosion validation
Every pipe has to clear either a hydrostatic test or a nondestructive electric test, eddy-current or ultrasonic, on top of the mechanical and process tests. Supplementary corrosion tests get added when specified.
| Test | Basis | Purpose |
|---|---|---|
| Hydrostatic OR nondestructive electric | Required (one of two) | Pressure integrity / flaw detection |
| Flattening | Required | Ductility and weld soundness |
| Hardness | Required | Confirms proper solution annealing |
| Tension | Required | Verifies strength minima |
| ASTM A923 / ASTM G48 | Supplementary | Intermetallic-phase and pitting resistance |
Crestflo backs its duplex product with in-house NDT, hydraulic proof and burst testing, destructive testing at ISO/IEC 17025-accredited labs, and PMI on material. Duplex and super-duplex forms ship standard with an EN 10204 3.1 material test certificate (3.2 on request), plus a heat/lot number on every part. See EN 10204 material test certificates and material traceability for more. Third-party inspection can be arranged on request.
ASTM A790 vs A789: duplex pipe vs duplex tube
A790 and A789 trip people up more than any other pairing. They're sibling duplex standards, but the split comes down to product form and how sizing gets measured.
| Attribute | ASTM A790 (pipe) | ASTM A789 (tube) |
|---|---|---|
| Product form | Pipe | Tubing (small diameter) |
| Sizing basis | Nominal pipe size / schedule (B36.19M) | OD × wall thickness |
| Typical use | Fluid and gas transport | Heat exchangers, instrumentation |
| Material family | Duplex / super-duplex | Duplex / super-duplex |
| Crestflo relevance | Material grade reference | Tube ordered to this spec |
In short: A790 = duplex pipe; A789 = duplex tube. Same alloy family, different product form. Crestflo manufactures duplex and super-duplex instrumentation and process tubing to A789, not mill pipe. For sour service, duplex is additionally qualified against NACE MR0175 / ISO 15156; for North Sea projects, material data-sheet conformance is set by NORSOK M-630.
Related and companion standards to ASTM A790
A790 rarely shows up alone on a duplex project. The standards below cover the adjacent product forms and service conditions it works alongside.
| Standard | Governs | Reference |
|---|---|---|
| ASTM A789 | Duplex stainless tube | ASTM A789 |
| ASTM A928 | Duplex pipe welded with filler metal | Companion pipe spec |
| ASTM A815 | Duplex wrought fittings | Fitting form |
| ASTM A182 | Duplex forgings and flanges | ASTM A182 |
| ASTM A479 | Duplex bar and shapes | ASTM A479 |
| ASTM A312 | Austenitic stainless pipe | ASTM A312 |
| NACE MR0175 / ISO 15156 | Sour-service metallurgy | ISO 15156 |
EN 10216-5 (seamless) and EN 10217-7 (welded) come closest, though neither matches A790 point for point. The grades keep the same Werkstoff (DIN) numbers noted above: 1.4462 for 2205, 1.4410 for 2507, and 1.4501 for Zeron 100.
ASME SA-790 relationship
SA-790 is ASTM A790 as adopted into the ASME Boiler & Pressure Vessel Code. That "SA" prefix flags code adoption; the chemistry, mechanical properties and test requirements match the ASTM document, just applied inside the BPVC framework. So a grade like SA-790 S31803 is the same material as A790 S31803, only specified for code work. Duplex pipe made to A790/SA-790 is commonly routed through ASME B31.3 process piping.
Where ASTM A790 duplex pipe is used
Offshore and subsea process lines, chemical and petrochemical plants, marine systems, seawater cooling and desalination, pulp-and-paper bleaching circuits, flue-gas desulfurization (FGD), these are the places where A790 duplex and super-duplex pipe earns its keep, wherever chloride and pressure push hardest. High strength paired with real resistance to pitting and stress-corrosion cracking explains why it takes over from 316L once conditions turn brackish, marine or heavy with chloride.
Source duplex material to ASTM A790 / A789 from Crestflo: request a quote
Crestflo is a US-serving manufacturer of Duplex 2205 and Super-Duplex 2507 instrumentation and process tubing, fittings and valves, the duplex product forms that carry over from A790's grade metallurgy into instrumentation service. Crestflo's tubing is ordered to the companion tube standard ASTM A789; for A790 duplex pipe and other mill forms, or a specific grade and size, share your requirement and our engineering team will scope it. Material is of Indian origin, with US / European melt available on request and full material traceability. Ready stock for standard items, made-to-order for specials, with 6–8 week delivery, cost-competitive after US duties. The company is ISO 9001 / 14001 / 45001 & PED certified, and delivers EN 10204 3.1 certification (3.2 on request), heat-number marking and PMI on every order.
Explore duplex and alloy instrumentation tubing, Duplex 2205 tubing and Super-Duplex 2507 tubing. Request a quote, request a sample, or explore the distributor program.
Why Crestflo for duplex and super-duplex material
Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house with a track record of deliveries across the Middle East, and that heritage backs a new manufacturing brand. Buyers get a US-serving source with the kind of transparent traceability offshore mills simply don't offer: EN 10204 3.1/3.2 certificates, heat-number marking on every part, in-house NDT, 17025-accredited destructive testing, small MOQ, private-label capability, and a 6-8 week lead time against the 20-plus weeks common with the majors. Learn more at Why Crestflo.
Frequently asked questions about ASTM A790
What material is ASTM A790?
ASTM A790/A790M sets the standard for seamless and welded ferritic/austenitic (duplex) stainless steel pipe. It covers grades like S31803, S32205 (2205), S32750 (2507) and S32760 (Zeron 100), along with their chemistry, mechanical properties and the tests each one requires.
Is ASTM A790 seamless or welded?
Both. A790 covers seamless pipe and straight-seam welded pipe made without added filler metal. Weld duplex pipe with added filler metal, though, and it falls under ASTM A928 instead.
What is the difference between ASTM A790 and A789?
A790 covers duplex stainless pipe. It's sized by nominal pipe size and schedule, and it's meant for moving fluids and gases. A789, on the other hand, covers duplex tube, sized by outside diameter and wall thickness, and it's built for heat-exchanger and instrumentation service. The alloy families match up. What changes is the product form and the dimensional tables that go with it.
Which grades does ASTM A790 cover?
Duplex and super-duplex UNS grades include S31803 and S32205 (2205), S32304 (2304 lean duplex), S32550 (Ferralium 255), S32750 (2507), and S32760 (Zeron 100), along with other ferritic/austenitic grades covered in the current edition.
Is 254 SMO covered by ASTM A790?
254 SMO (UNS S31254) belongs to the super-austenitic family, not the duplex family. Its pipe spec falls under ASTM A312, while A790 covers the ferritic/austenitic, or duplex, group instead.
What tests does ASTM A790 require?
A hydrostatic test or a nondestructive electric test using eddy-current or ultrasonic methods is required, along with flattening, hardness and tension tests. When specified, supplementary tests for intermetallic phase and pitting resistance, such as ASTM A923 and G48, are also carried out.
Is ASTM A790 the same as ASME SA-790?
SA-790 is ASTM A790 as adopted into the ASME Boiler & Pressure Vessel Code. The technical requirements don't change; the SA designation simply flags that it's being used in a code context.
Does A790 duplex meet NACE MR0175 for sour service?
A790 sets the base metallurgy. Sour-service acceptance is governed separately under NACE MR0175 / ISO 15156, which adds hardness and phase-balance limits. Crestflo supplies duplex to NACE MR0175 on request.
Can Crestflo supply material to ASTM A790 or A789?
Crestflo makes Duplex 2205 and Super-Duplex 2507 instrumentation and process tubing, fittings and valves, with tubing ordered to ASTM A789 and full EN 10204 3.1/3.2 traceability. For A790 pipe and other mill forms, just send over your grade, size and quantity, and our engineering team will scope it.
Where can I get the official ASTM A790 PDF or document?
The official ASTM A790 PDF is published and sold by ASTM International. Crestflo references A790 for material supply but doesn't distribute the copyrighted document.
Related standards and materials
- ASTM A789, duplex stainless tubing
- ASTM A312, austenitic stainless pipe
- ASTM A182, duplex forgings and flanges
- 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
Crestflo publishes both the 2205 and 2507 material pages alongside the comparison guide, so anyone weighing duplex against super-duplex can check the standards in one place.