COMPREHENSIVE TECHNICAL ANALYSIS AND DATASHEET OF ASTM A194 GRADE 8MLCuN NUTS
ASTM A194 Grade 8MLCuN specifies premium super-austenitic stainless steel nuts, famously known in the industry as 254 SMO® or UNS S31254. This high-performance "6% Moly" grade is heavily alloyed with Molybdenum, Copper, and Nitrogen, while maintaining an exceptionally low carbon profile. These powerful alloying elements work synergistically to provide extraordinary resistance to pitting, crevice corrosion, and chloride stress corrosion cracking, significantly outperforming standard 300-series stainless steels in aggressive halogen environments.
Grade 8MLCuN components are the benchmark choice for severe marine, offshore oil & gas, and pulp & paper environments where standard 316L or 317L stainless steel would rapidly suffer from localized corrosion failure.
■ Product Overview & Specifications
| Material Classification | Super Austenitic Stainless Steel (6% Moly Grade) |
|---|---|
| UNS Designation | S31254 |
| Microstructure | Austenitic (Nitrogen-Strengthened) |
| Magnetic State | Non-Magnetic |
| Density | ~8.00 g/cm³ (0.289 lb/in³) |
| Size Range | Metric: M6 to M100 | Imperial: 1/4" to 4" |
| Thread Types | UNC, UNF, 8UN, Metric Coarse, Metric Fine |
■ Proprietary Datasheet Download (GATED)
ASTM A194 Grade 8MLCuN — Complete Technical Datasheet
Contains detailed proof load thresholds, dimensional tolerances for ASME B18.2.2 standard and heavy hex profiles, and critical Pitting Resistance Equivalent Number (PREN) data.
⬇ DOWNLOAD DATASHEET■ MTC Integration Section
Material traceability is the backbone of safety in high-pressure environments. Every lot shipped by Ananka is accompanied by fully authenticated documentation mapping back to raw steel mill certificates.
- EN 10204 Type 3.1: Issued by our independent quality department, providing specific heat-traceable test results (actual chemical analysis, mechanical test results, hardness, and proof load tests).
- EN 10204 Type 3.2: For critical commercial, offshore, or chemical applications, we facilitate third-party witness testing.
■ Chemical Composition
The corrosion resistance of Grade 8MLCuN is driven by its incredibly rich chemistry. The 6% Molybdenum addition provides extreme resistance to chloride pitting, while the Nitrogen boosts mechanical yield strength. The ultra-low carbon content (Max 0.020%) prevents sensitization during welding and high-temperature service.
| Carbon (C) | Manganese (Mn) | Chromium (Cr) | Nickel (Ni) | Molybdenum (Mo) | Phosphorus (P) | Sulfur (S) | Silicon (Si) |
|---|---|---|---|---|---|---|---|
| 0.020 Max | 1.00 Max | 19.5 – 20.5 | 17.5 – 18.5 | 6.0 – 6.5 | 0.030 Max | 0.010 Max | 0.80 Max |
■ Mechanical Properties
| Mechanical Property | Grade 8MLCuN Limits |
|---|---|
| Hardness Limit (Rockwell) | 32 HRC Maximum |
| Proof Load | Dependent on Size |
■ Equivalent Grades & Designations
| Standard / System | Designation |
|---|---|
| ASME Standard | SA194 Grade 8MLCuN |
| Common Trade Name | 254 SMO®, 6% Moly Nuts, UNS S31254 |
| European Equivalent | EN 1.4547 / X1CrNiMoCuN20-18-7 |
■ Applications & Industries
- Marine & Offshore: Seawater cooling systems, offshore oil & gas platforms, and subsea structural fastening where chloride-induced pitting is a severe threat.
- Desalination Plants: High-pressure reverse osmosis (RO) systems handling highly concentrated brine.
- Chemical & Petrochemical: Bleaching plants in the pulp and paper industry, flue gas desulfurization (FGD) scrubbers, and vessels handling tall oil.
■ Compatible Fastener Assemblies
| Internal Threads (A194 Gr 8MLCuN) | Mating Bolts (A193 Gr B8MLCuN) | Mating Studs (A193 Gr B8MLCuN) |
|---|---|---|
| Grade 8MLCuN Heavy Hex Nuts | ASTM A193 Grade B8MLCuN Hex Bolts | A193 Grade B8MLCuN Fully Threaded Studs |
■ Torque & Installation Guidelines
Due to the incredibly high alloy content and the austenitic nature of 8MLCuN, thread galling is a significant risk under high clamping loads. Premium, heavy-duty anti-seize lubrication (such as nickel or molybdenum-disulfide based pastes) is absolutely mandatory for installation.
| Nominal Diameter | Threads Per Inch (UNC) | Target Torque — Lubricated (ft-lbs) |
|---|---|---|
| 1/2" | 13 | 45 |
| 5/8" | 11 | 90 |
| 3/4" | 10 | 150 |
| 1" | 8 | 350 |
■ Frequently Asked Questions
1. What does the "MLCuN" stand for?
The letters indicate the critical alloying additions that set this grade apart from standard 316 stainless: Molybdenum (high levels for pitting resistance), Low Carbon (prevents sensitization), Cupper (improves resistance to certain acids like sulfuric acid), and Nitrogen (increases yield strength and stabilizes the austenite phase).
2. How does Grade 8MLCuN compare to Grade 8M (Type 316)?
Grade 8M (Type 316) contains about 2-3% Molybdenum and is suitable for moderate chloride environments. Grade 8MLCuN contains over 6% Molybdenum, giving it a much higher Pitting Resistance Equivalent Number (PREN > 42). It will survive in aggressive hot seawater and chemical bleach environments where Type 316 would rapidly fail.
3. Is Grade 8MLCuN a Duplex stainless steel?
No, it is a fully Super Austenitic stainless steel. While its corrosion resistance is often compared to (and sometimes exceeds) Super Duplex grades like 2507, its fully austenitic microstructure gives it superior ductility and toughness, especially at extremely low (cryogenic) temperatures.