RAYCHIN LIMITED

Complete Range of 254 SMO Nuts

Manufacturing Standards for 254 SMO Nuts

RAYCHIN LIMITED manufactures 254 SMO nuts to the following national and international standards, ensuring full compliance for projects worldwide. Both standard and non-standard custom configurations are available.

International Standards & Global Designations for 254 SMO Nuts

To serve clients worldwide, RAYCHIN LIMITED manufactures 254 SMO nuts from material conforming to the following national and international specifications. This ensures full compliance for projects in the Americas, Europe, Asia, and the Middle East.

UNS S31254 1.4547 X1CrNiMoCuN20-18-7 ASTM A479 NACE MR0175

Chemical Composition (Weight %) – 254 SMO Super Austenitic Stainless Steel

Our 254 SMO nuts are produced from melts that strictly conform to the limits below per ASTM A479 / UNS S31254. The high levels of chromium, molybdenum, and nitrogen provide exceptional resistance to pitting and crevice corrosion, with a Pitting Resistance Equivalent (PRE) of ≥42.5. The PRE is calculated as %Cr + 3.3 × %Mo + 16 × %N.

Expert note: The high molybdenum (6%) and nitrogen content gives 254 SMO a PRE value ≥42.5, providing resistance to pitting and crevice corrosion in seawater and other chloride environments that is far superior to 316L (PRE≈24) and 317L (PRE≈29). This makes 254 SMO nuts ideal for offshore, desalination, and FGD applications.

Complete Mechanical Properties of 254 SMO Nuts (Solution Annealed Condition)

254 SMO nuts are supplied in the solution annealed condition (1150–1200°C followed by water quenching). The data below represent minimum values per ASTM A479 and EN 10088-3. Nuts are proof load tested to ensure compatibility with mating bolts.

Mechanical Properties at Room Temperature

High Temperature Performance of 254 SMO Nuts

254 SMO maintains good mechanical properties at elevated temperatures, though it should not be exposed to temperatures between 600–1000°C for prolonged periods due to the risk of intermetallic phase precipitation. For continuous service, the maximum operating temperature is approximately 400°C. The steel has very good impact strength at both room and cryogenic temperatures.

Temperature-Dependent Yield Strength (0.2% Offset)

Note: Intermetallic phases precipitate within the temperature range of 600–1000°C. Therefore, 254 SMO should not be exposed to these temperatures for prolonged periods. For applications requiring strength retention above 400°C, alternative alloys should be considered.

Thermal Stability Limits

Corrosion Resistance of 254 SMO Nuts

254 SMO was specifically developed for use in aggressive chloride-bearing environments. Its high molybdenum (6%) and nitrogen content provide exceptional resistance to localized corrosion, including pitting, crevice corrosion, and stress corrosion cracking.

Pitting and Crevice Corrosion Resistance

The Pitting Resistance Equivalent (PRE) for 254 SMO is ≥42.5, calculated as PRE = %Cr + 3.3 × %Mo + 16 × %N. This value is significantly higher than 316L (PRE ≈ 24) and 317L (PRE ≈ 29), indicating superior resistance to pitting and crevice corrosion in chloride environments such as seawater. Tests in natural seawater at 60°C (140°F) have shown that 254 SMO can be exposed for prolonged periods without suffering crevice corrosion.

Stress Corrosion Cracking (SCC) Resistance

Ordinary austenitic steels (304, 316) are prone to chloride stress corrosion cracking at temperatures above 60°C. 254 SMO, with its high nickel and molybdenum content, exhibits excellent resistance to SCC. In boiling 25% NaCl solution (pH=1.5) U-bend tests, 254 SMO showed no failure after 1000 hours, while AISI 316 failed in less than 150 hours.

Intergranular Corrosion

With its very low carbon content (≤0.020%), 254 SMO has minimal risk of carbide precipitation during heating. The steel passes the Strauss test (ASTM A262, practice E) even after sensitizing for one hour at 600–1000°C, demonstrating excellent resistance to intergranular corrosion.

Critical Corrosion Considerations for Nuts

• PRE ≥42.5: The high Pitting Resistance Equivalent ensures outstanding performance in seawater and aggressive chemical environments.
• NACE MR0175 Compliance: 254 SMO is qualified for sour service (sulfide stress cracking resistance) in oilfield equipment per NACE MR0175/ISO 15156.
• Temperature Limitations: Avoid prolonged exposure to 600–1000°C to prevent intermetallic phase precipitation, which can affect corrosion resistance.
• Galvanic Corrosion: When paired with lower-grade materials, galvanic corrosion should be considered. 254 SMO is cathodic to most other stainless steels.
• Welding: The low carbon content ensures no risk of intergranular corrosion after welding.

Corrosion Engineering Note: For critical applications in aggressive environments, RAYCHIN LIMITED can provide passivation, specialized coatings (Xylan, PTFE, silver plating), or recommend optimal heat treatment conditions. Third-party corrosion testing per ASTM G31, G48, or G61 available upon request. NACE MR0175 compliant 254 SMO nuts available for sour service applications.

Why RAYCHIN LIMITED – The 254 SMO Nut Authority