ASTM A790 / A790M — Seamless and Welded Duplex Stainless Steel Pipe
ASTM A790/A790M (latest edition: A790M-23) is the primary specification for seamless and welded ferritic-austenitic (duplex) stainless steel pipe for pressure piping service. ASME SA-790 is adopted in BPVC Section II Part A. Duplex pipe to A790 is the direct complement to A789 (tubing) — both cover the same grades but A790 addresses pressure piping with NPS-based dimensions per ASME B36.19.
1. Scope
A790 covers pipe from NPS ⅛ (DN 6) through NPS 36 (DN 900) and larger, in wall thicknesses per ASME B36.19 schedules 5S through 80S. The pipe may be seamless (hot- or cold-finished) or welded (EFW, SAW, SMLS from tube rounds). Both straight-length and random-length supply conditions are permitted.
2. Grades Covered
| UNS No. |
Common Name |
Type |
PREN |
Key Feature |
| S32101 |
LDX 2101 |
Lean Duplex |
~26 |
Low Ni (1.5%), Mn-alloyed; cost-effective |
| S32304 |
2304 |
Lean Duplex |
~26 |
Mo-free; better SCC resistance than 316L |
| S31803 |
2205 (original) |
Standard Duplex |
~32 |
Original 2205 composition |
| S32205 |
2205 (revised) |
Standard Duplex |
~35 |
Higher Cr, N minimums vs S31803; preferred grade |
| S32750 |
2507 super duplex |
Super Duplex |
~43 |
25Cr-7Ni-4Mo; highest PREN in A790 |
| S32760 |
Zeron 100 |
Super Duplex |
~41 |
W + Cu additions; offshore umbilicals |
3. Chemical Composition
| UNS / Grade |
C max |
Cr |
Ni |
Mo |
N |
Others |
| S32101 |
0.040 |
19.5–21.5 |
1.35–1.70 |
0.10–0.80 |
0.20–0.25 |
Mn 4.0–6.0 |
| S32304 |
0.030 |
21.5–24.5 |
3.0–5.5 |
0.05–0.60 |
0.05–0.20 |
— |
| S31803 |
0.030 |
21.0–23.0 |
4.5–6.5 |
2.5–3.5 |
0.08–0.20 |
— |
| S32205 |
0.030 |
22.0–23.0 |
4.5–6.5 |
3.0–3.5 |
0.14–0.20 |
— |
| S32750 |
0.030 |
24.0–26.0 |
6.0–8.0 |
3.0–5.0 |
0.24–0.32 |
Cu ≤0.50 |
4. Mechanical Properties
| Grade |
UTS min (MPa) |
YS min (MPa) |
Elong. min (%) |
Hardness max (HBW) |
| S32101 |
655 |
450 |
30 |
293 |
| S32304 |
600 |
400 |
25 |
290 |
| S31803 / S32205 |
620 |
450 |
25 |
293 |
| S32750 |
795 |
550 |
15 |
310 |
5. Heat Treatment and Quality
All A790 pipe must be solution-annealed and water-quenched. The solution temperature for S32205 is 1020–1100 °C; for S32750 it is 1050–1150 °C. Pipe is subject to the same ASTM A923 intermetallic phase verification as A789 tubing.
6. Testing Requirements
| Test |
Requirement |
| Tensile |
One per heat or heat-treatment lot |
| Hydrostatic |
Each pipe length; alternative: 100% ET or UT when specified |
| Hardness |
Spot-check; 100% on S32750 for critical service |
| Chemical Analysis |
One ladle per heat; product analysis on request |
| Ferrite (A923) |
As specified in purchase order |
| Visual & Dimensional |
100%; OD/wall per ASME B36.19 tolerances |
7. Comparison: A790 Duplex vs A312 Austenitic Pipe
| Parameter |
A790 S32205 (2205) |
A312 TP316L |
| YS min (MPa) |
450 |
170 |
| UTS min (MPa) |
620 |
485 |
| Wall thickness (same P-T) |
~55% of 316L wall |
Baseline |
| Chloride SCC resistance |
Excellent |
Poor (susceptible above ~60 °C) |
| Min service temperature |
–29 °C |
–196 °C (cryogenic) |
| Max continuous service |
316 °C |
816 °C |
| Cost (relative) |
~1.2× 316L (by weight); lower cost per pressure-unit |
Baseline |
8. Related Standards and How to Order
| Standard |
Description |
| ASTM A789 / SA-789 |
Duplex SS tubing (companion specification) |
| ASTM A815 / SA-815 |
Duplex SS butt-welding fittings |
| ASTM A312 / SA-312 |
Austenitic SS pipe (for comparison) |
| ASME B36.19 |
Stainless steel pipe dimensions (5S, 10S, 40S, 80S schedules) |
When ordering A790, specify: ASTM A790M-23 or ASME SA-790 + Grade (UNS No.) + NPS + Schedule + Seamless or Welded + Heat treatment (solution-annealed) + Certificate (EN 10204 3.1) + NACE MR0175 if sour service.
HT PIPE supplies ASTM A790 duplex stainless steel pipe in S32205 and S32750, NPS ½–24 seamless and welded, with EN 10204 3.1 and NACE MR0175 compliance.
