254SMO (UNS S31254) Seamless Stainless Steel Pipe- High-Alloy Super Austenitic Solution
Overview of 254SMO Seamless Pipe
254SMO UNS S31254 Seamless Stainless Steel Pipe is supplied for 6Mo super-austenitic chemistry for high pitting and crevice-corrosion resistance. The size range shown (OD 6–1016 mm; WT 0.5–65 mm) is the overall capability across this product family, not a per-grade commitment. Confirm the specific OD × WT × length combination for the ordered grade in the quotation. The governing specification must be stated on the purchase order: ASTM A312 / ASME SA312, UNS S31254. Chemistry, mechanical properties, heat treatment, dimensional tolerance, NDT and certification must be reported against the ordered standard and material heat; do not treat typical values as guaranteed acceptance limits.
As a leading supplier, we provide 254SMO seamless pipes that combine exceptional mechanical strength with outstanding lifecycle cost-efficiency. Our seamless manufacturing process ensures uniform wall thickness and enhanced pressure-retaining capabilities, critical for high-integrity applications in marine, chemical, and offshore industries.
Product-Specific Standards for Seamless Pipe
The manufacture and application of 254SMO seamless pipe are governed by stringent industry standards to ensure quality, reliability, and safety. The primary American Society for Testing and Materials (ASTM) and American Society of Mechanical Engineers (ASME) specifications include:
ASTM A312 / ASME SA312: Standard specification for seamless and welded austenitic stainless steel pipes.
ASTM A213 / ASME SA213: For seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes.
ASTM A269: Seamless and welded austenitic stainless steel tubing for general service.
Pressure Compliance: Approved by the ASME Boiler and Pressure Vessel Code (Section VIII, Division 1) for reliable use in high-pressure operational environments.
Equivalent Grade
| UNS | Common grade name | EN material number | EN steel name | JIS grade | GB/T grade |
|---|---|---|---|---|---|
| S31254 | 254 SMO | 1.4547 | X1CrNiMoCuN20-18-7 | SUS312L | 015Cr20Ni18Mo6CuN |
Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. See the grade designation index.
Chemical Composition
The specific role of each key element is critical to understanding the alloy’s overall performance:
- Chromium (Cr): At 19.5% to 20.5%, chromium is the primary element responsible for forming the passive oxide layer on the steel’s surface, which provides foundational corrosion resistance.
- Nickel (Ni): With a high content of 17.5% to 18.5%, nickel stabilizes the austenitic crystal structure. This imparts the material with exceptional ductility, toughness, and, most importantly, provides superior resistance to chloride-induced stress corrosion cracking (SCC) compared to standard 300-series grades.
- Molybdenum (Mo): The”super”element, with its high content of 6.0% to 7.0%, is the single most important factor for enhancing pitting and crevice corrosion resistance. This is particularly effective in halide environments, such as those with high concentrations of chlorides.
- Nitrogen (N): The addition of nitrogen (0.18% to 0.25%) serves a dual purpose. It works synergistically with molybdenum to significantly boost pitting resistance, and it also contributes to the material’s high mechanical strength.
- Copper (Cu): The addition of copper (0.50% to 1.00%) improves the alloy’s resistance to sulfuric acid and other non-oxidizing acids.The low carbon content (<0.020%) is also a vital feature, as it minimizes the risk of carbide precipitation during heating, which could otherwise lead to intergranular corrosion, especially in the heat-affected zone of welds.
| Cr | Ni | P | S | Mo | Cu | N | Mn | Si | C |
|---|---|---|---|---|---|---|---|---|---|
| 19.50 – 20.50 | 17.50 – 18.50 | ≤ 0.030 | ≤ 0.010 | 6.00 – 6.50 | 0.50 – 1.00 | 0.18 – 0.25 | ≤ 1.00 | ≤ 0.80 | ≤ 0.020 |
Data source: ASTM A312-25 / ASME SA312 Table 1, UNS S31254 ≤ heat-analysis acceptance limits (element maxima unless a range is shown). Confirm the values against the ordered edition and the MTC.
Typical Mechanical Properties
254SMO stainless steel (UNS S31254 / EN 1.4547) is specifically engineered to retain high strength and dimensional stability in high-stress, chloride-rich and corrosive environments.
| Tensile Strength (min) | Yield Strength (min) | Elongation | Hardness. |
|---|---|---|---|
| t ≤ 0.187 in. [5.00 mm]: 98 ksi [675 MPa]; t > 0.187 in.: 95 ksi [655 MPa] | 45 ksi [310 MPa] | ≥ 35% | ≤ 192 HBW |
Note: Typical values for reference only — not acceptance limits. Mechanical properties are reported on the MTC against the ordered standard, product form, condition and test temperature.
Typical Physical Properties
These physical properties highlight the material’s ability to perform reliably under a wide range of conditions.
| Density | Melting Point | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 8.0 g/cm3 | 1300 – 1390 °C approx. | 16.5 μm/m·°C (20-100°C) | 13.9 W/m·K (20°C) | 195 GPa | 0.85 × 10⁻⁶ Ω·m (20°C) |
Note: Typical values for reference only — not acceptance limits. Physical and mechanical properties are reported on the MTC against the ordered standard, product form and condition.
Size Tolerance Chart (mm)
| NPS Designator (Inches) | Permissible Variations in Outside Diameter (Inches) |
| 1⁄8 to 1 1⁄2, inclusive | Over: 1⁄64 in. (0.015 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 1 1⁄2 to 4, inclusive | Over: 1⁄32 in. (0.031 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 4 to 8, inclusive | Over: 1⁄16 in. (0.062 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 8 to 18, inclusive | Over: 3⁄32 in. (0.093 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 18 to 26, inclusive | Over: 1⁄8 in. (0.125 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 26 to 34, inclusive | Over: 5⁄32 in. (0.156 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 34 to 48, inclusive | Over: 3⁄16 in. (0.187 in.) |
| Under: 1⁄32 in. (0.031 in.) |
Tolerance basis: permitted variations per the governing specification stated on this page and the applicable general-requirements standard (ASTM A999 / ASME SA999) for the ordered product form; the wall-thickness and length variations in this section follow the same basis.
The wall thickness tolerances are defined by the nominal wall thickness (t) and the outside diameter (D).
1. Minimum Wall Thickness
The minimum wall thickness at any point on the pipe shall not be more than {12.5%} under the nominal (specified) wall thickness.
2. Maximum Wall Thickness (Percentage Over Nominal)
The maximum allowable wall thickness variation depends on the size and the t/D ratio (ratio of nominal wall thickness to ordered outside diameter):
| NPS Designator (Inches) | t/D Ratio | Permissible Variation (Over Nominal WT) |
| 1/8 to 2, inclusive | All ratios | +20.0% |
| 3 to 18, inclusive | t/D ≤ 5% | +22.5% |
| 3 to 18, inclusive | t/D >5% | +15.0% |
| 20 and larger (Seamless) | t/D ≤ 5% | +22.5% |
| 20 and larger (Seamless) | t/D >5% | +15.0% |
| 20 and larger (Welded) | All ratios | +17.5% |
For pipe ordered to a Specific Cut Length, the standard tolerance is +1⁄8 in. [3.2 mm], -0 in. [0 mm].
Pipe is typically supplied in Single Random Lengths (17 to 24 ft) or Double Random Lengths (38 to 40 ft), unless otherwise specified.
Disclaimer: These tolerances are based on ASTM A999/A999M general dimensional requirements commonly referenced by ASTM A312 and ASTM A790. The full and most current specification document must always be consulted for official design and procurement purposes.
Conclusion
A312 254SMO Seamless Stainless Steel Pipe and tube represents a pinnacle of material engineering, offering an unparalleled blend of corrosion resistance and mechanical strength. Its strategic alloy composition, particularly the high levels of molybdenum and nitrogen, provides a quantitative and verifiable advantage against pitting, crevice corrosion, and stress corrosion cracking in aggressive environments. When manufactured in a seamless form, the material’s inherent structural integrity is fully realized, providing a product with uniform strength and enhanced pressure capacity, free from the inherent weaknesses of a welded seam. For industries such as marine and offshore engineering, chemical processing, and oil and gas, where system integrity is non-negotiable, 254SMO seamless pipe is not simply a material choice; it is a fundamental component of a reliable and safe operational strategy.
Frequently Asked Questions
What sizes are available for 254SMO seamless pipe?
The overall range is OD 6–1016 mm; WT 0.5–65 mm. Requirements outside this range are reviewed against mill capability on request.
Which specification governs 254SMO seamless pipe?
ASTM A312 / ASME SA312, UNS S31254 is the governing specification for 254SMO seamless pipe. The edition in force at order time is stated on the quotation and purchase order; chemistry, mechanical properties, heat treatment, dimensions and testing are reported against the ordered standard and material heat.
What inspection documents are provided?
Each order is documented with a mill test certificate stating heat chemistry and mechanical test results. EN 10204 3.1 certification, hydrostatic testing, eddy-current or ultrasonic inspection and PMI are performed when specified in the purchase order.
Technical review: page data reviewed by the Xinzhe technical desk on 2026-09-27. Chemistry acceptance limits are compiled from the governing ASTM/ASME specification stated on this page; mechanical and physical values are typical reference data and are not acceptance guarantees. Values must be confirmed against the standard edition in force at order time and the material test certificate.
Ready to Request a Quotation?
Send the NPS and schedule (or actual OD and wall), quantity, length, end finish and the inspection items you need as acceptance criteria — you will get a written quotation stating the specification and edition, delivery condition, documents included and lead time.
For the same grade in tube form, see the 254SMO seamless tube. To compare other grades and size combinations, browse the Stainless Steel Seamless Tube category. Minimum order quantity and lead time are confirmed on enquiry against the ordered grade, size and quantity.
