904L / 6Mo stainless steel seamless pipe covers two UNS-designated super-austenitic options in ASME SA-312: 904L is N08904 and the 6Mo grade shown here is S31254. This corrects a common catalogue error: S32654 is 654 SMO, not 904L. The two grades on this page are related but not interchangeable.
904L combines 4.0–5.0 % Mo with 1.00–2.00 % Cu and nitrogen capped at 0.10 %. S31254 raises Mo to 6.0–6.5 % and requires 0.18–0.25 % N. Their solution-annealing minima and tensile requirements differ, so the purchase order and MTC must carry the UNS number rather than only ‘super austenitic’.
Grade, UNS and Specification
| Common name | UNS | SA-312 identity | Mo, % | Anneal minimum |
|---|---|---|---|---|
| 904L | N08904 | UNS-designated austenitic grade | 4.0–5.0 | 2000 °F [1100 °C] |
| 6Mo | S31254 | UNS-designated super-austenitic grade | 6.0–6.5 | 2100 °F [1150 °C] |
Chemical Composition (ASME SA-312 Table 1)
| Element, weight % | 904L (N08904) | 6Mo (S31254) |
|---|---|---|
| Carbon, max | 0.020 | 0.020 |
| Manganese, max | 2.00 | 1.00 |
| Phosphorus, max | 0.040 | 0.030 |
| Sulfur, max | 0.030 | 0.010 |
| Silicon, max | 1.00 | 0.80 |
| Chromium | 19.0–23.0 | 19.5–20.5 |
| Nickel | 23.0–28.0 | 17.5–18.5 |
| Molybdenum | 4.0–5.0 | 6.0–6.5 |
| Nitrogen | 0.10 max | 0.18–0.25 |
| Copper | 1.00–2.00 | 0.50–1.00 |
Tensile Requirements (ASME SA-312 Table 4)
| Grade / wall | Tensile min, ksi (MPa) | 0.2 % yield min, ksi (MPa) | Elongation longitudinal / transverse, min % |
|---|---|---|---|
| N08904 | 71 (490) | 31 (215) | 35 / 25 |
| S31254, t ≤ 0.187 in. (5.00 mm) | 98 (675) | 45 (310) | 35 / 25 |
| S31254, t > 0.187 in. (5.00 mm) | 95 (655) | 45 (310) | 35 / 25 |
Size Range and OD × Wall
| NPS | OD, in. (mm) | Sch 5S wall, in. (mm) | Sch 10S wall, in. (mm) | Sch 40S wall, in. (mm) | Sch 80S wall, in. (mm) |
|---|---|---|---|---|---|
| 1/2 | 0.84 (21.34) | 0.065 (1.65) | 0.083 (2.11) | 0.109 (2.77) | 0.147 (3.73) |
| 3/4 | 1.05 (26.67) | 0.065 (1.65) | 0.083 (2.11) | 0.113 (2.87) | 0.154 (3.91) |
| 1 | 1.315 (33.4) | 0.065 (1.65) | 0.109 (2.77) | 0.133 (3.38) | 0.179 (4.55) |
| 1-1/2 | 1.9 (48.26) | 0.065 (1.65) | 0.109 (2.77) | 0.145 (3.68) | 0.2 (5.08) |
| 2 | 2.375 (60.33) | 0.065 (1.65) | 0.109 (2.77) | 0.154 (3.91) | 0.218 (5.54) |
| 3 | 3.5 (88.9) | 0.083 (2.11) | 0.12 (3.05) | 0.216 (5.49) | 0.3 (7.62) |
| 4 | 4.5 (114.3) | 0.083 (2.11) | 0.12 (3.05) | 0.237 (6.02) | 0.337 (8.56) |
| 6 | 6.625 (168.28) | 0.109 (2.77) | 0.134 (3.4) | 0.28 (7.11) | 0.432 (10.97) |
| 8 | 8.625 (219.08) | 0.109 (2.77) | 0.148 (3.76) | 0.322 (8.18) | 0.5 (12.7) |
| 10 | 10.75 (273.05) | 0.134 (3.4) | 0.165 (4.19) | 0.365 (9.27) | 0.5 (12.7) |
| 12 | 12.75 (323.85) | 0.156 (3.96) | 0.18 (4.57) | 0.375 (9.52) | 0.5 (12.7) |
Selected rows from ANSI B36.19 Table 1 as reproduced in the ASME library. NPS is a designation; the OD shown is the controlling outside diameter. Other schedules and sizes are subject to the specification and enquiry. Wall tolerance is governed separately by SA-312 Table 3.
Manufacturing Route and Heat Treatment
Both grades are solution annealed and rapidly cooled, but SA-312 Table 2 sets different minimum temperatures: 2000 °F [1100 °C] for N08904 and 2100 °F [1150 °C] for S31254. Seamless manufacture may be followed by hot or cold finishing. Do not carry the general 1900 °F row for 304/316 across to these UNS rows; they are individually listed.
Inspection, Testing and Certification
- Heat and product verification: review heat number, UNS/grade, chemical analysis and the specified mechanical result against the named standard, not against a generic grade datasheet.
- Pipe tests: SA-312 Sections 11 and 13 cover tension/flattening and hydrostatic or nondestructive electric examination as applicable. Additional UT, eddy current, impact, PMI or hardness requirements must be defined on the order.
- Dimensions and surface: confirm actual OD, wall, length, end preparation and surface condition. Hydrostatic P = 2St/D is not a design-pressure calculation.
- Documentation: request the MTC route at enquiry stage. EN 10204 3.1 or 3.2, purchaser witnessing and third-party inspection are order-specific options to be confirmed in the quotation, not an automatic certificate bundle.
Packing & Delivery
Plastic end caps; steel frames or wooden crates for larger diameters; VCI protective wrapping where required. Beveled or plain ends are confirmed with the order. Marking should maintain the link between each length, standard, grade/UNS, size and heat number. Delivery schedule, quantity, MOQ and price are confirmed only against a specific enquiry.
Applications
Aggressive chemical-process lines, chloride-bearing process utilities after corrosion review, acid handling where concentration and temperature have been evaluated, offshore and desalination auxiliaries, pollution-control equipment, and high-integrity process manifolds. No universal chloride, acid-concentration or temperature limit is implied; media-specific review remains necessary.
Technical Notes
1. ‘6Mo’ is a chemistry family description, while S31254 is the acceptance identity. SA-312 gives S31254 a narrow Cr range of 19.5–20.5 %, Ni 17.5–18.5 %, Mo 6.0–6.5 % and N 0.18–0.25 %. N08904 instead carries higher nickel and deliberate copper. These differences affect both corrosion selection and welding-consumable review.
2. S31254 tensile strength is wall-dependent. At t ≤ 0.187 in. [5.00 mm], Table 4 requires 98 ksi [675 MPa] tensile; above that threshold it is 95 ksi [655 MPa], with 45 ksi [310 MPa] yield in both rows. N08904 has a single 71/31 ksi row. Recording only a catalogue ‘6Mo strength’ can therefore misstate the specified minimum.
3. Filler selection is not completed by the base-metal table. SA-312 Table 6 has no direct N08904 or S31254 filler row. Welding consumable, procedure qualification, heat input and any corrosion testing should be fixed by the project specification rather than inferred from ER316L practice. High alloy content also makes correct solution anneal and rapid cooling central to the delivered condition.
For standard Mo-bearing pipe compare 316/316L; for nickel-alloy options see the nickel alloy pipe guide.
Frequently Asked Questions
Is 904L the same as UNS S32654?
No. 904L is UNS N08904. S32654 is a different, higher-alloy grade commonly called 654 SMO. This page covers N08904 and S31254 only.
Which UNS is used here for 6Mo seamless pipe?
S31254. SA-312 specifies 6.0-6.5 % Mo and 0.18-0.25 % N for this grade.
Do 904L and 6Mo use the same annealing temperature?
No. SA-312 Table 2 gives 2000 F [1100 C] minimum for N08904 and 2100 F [1150 C] minimum for S31254, followed by rapid cooling.
Why are there two tensile rows for S31254?
The specified tensile minimum changes at 0.187 in. [5.00 mm] wall: 98 ksi at or below the threshold and 95 ksi above it; yield remains 45 ksi.
Can ER316L filler be assumed for these grades?
No. SA-312 Table 6 does not give a direct filler row for N08904 or S31254. The project welding specification should establish consumable and procedure requirements.
