ASTM A193 GRADE B8MLN & B8MLNA BOLTS — DATASHEET, DIMENSIONS & MECHANICAL PROPERTIES
Ananka Fasteners is a premier global manufacturer and supplier of ASTM A193 Grade B8MLN and B8MLNA Fasteners. Forged from high-purity AISI 316LN austenitic stainless steel (UNS S31653), these highly specialized fasteners represent the ultimate metallurgical synthesis for extreme marine and petrochemical environments, combining three distinct chemical strategies into a single, flawless alloy.
The addition of 2-3% Molybdenum ("M") guarantees supreme resistance to chloride-induced pitting. The ultra-low Carbon content ("L" ≤ 0.030%) ensures total immunity to weld-decay and intergranular corrosion in the heat-affected zone (HAZ). Finally, a precise Nitrogen charge ("N") provides interstitial solid solution strengthening, perfectly restoring the yield strength that is naturally lost when carbon is removed. While Grade B8MLN undergoes standard carbide solution treatment, the B8MLNA designation demands strict post-fabrication annealing. This eradicates all residual threading stress and caps the hardness at 90 HRB for severe sour-gas (H2S) service. All B8MLN/B8MLNA components are strictly supported by EN 10204 Type 3.1 Material Test Certificates (MTC).
■ Proprietary Datasheet Download
For lead welding metallurgists, offshore engineers, and NACE compliance auditors requiring empirical weld-decay profiles, PREN calculations, and interstitial nitrogen stress models for ASTM A193 B8MLN/B8MLNA, the complete technical datasheet must be accessed.
ASTM A193 B8MLN / B8MLNA — Complete Technical Yield & Weldability Datasheet
Contains empirical data for stress simulations, ASTM A262 intergranular corrosion test results, and marine pitting longevity models. Corporate credentials required.
⬇ ACCESS SECURE DATASHEET PORTAL■ Mill Test Certificate (MTC) Integration
Because the defining characteristics of B8MLN/B8MLNA rely on an extremely specific balance of elemental suppressants (Carbon) and enhancers (Nitrogen + Molybdenum), the EN 10204 3.1 Mill Test Certificate (MTC) is the absolute proof of component integrity. Ananka Fasteners’ MTCs for B8MLN explicitly guarantee:
- Triple-Chemistry Verification: Empirical spectrography proving the Carbon is strictly capped ≤ 0.030%, Molybdenum is 2.0-3.0%, and Nitrogen falls within the critical 0.10% to 0.16% structural window.
- Mechanical Baseline Proof: Destructive test verification proving the nitrogen compensation successfully hit the 30 ksi minimum yield threshold without cold-working.
- Post-Fabrication Verification (B8MLNA): An explicit statement confirming that carbide solution treatment was performed after all machining and threading.
- Hardness Limit Proof (B8MLNA): Guaranteed laboratory results proving the batch hardness is fully capped below 90 HRB for severe NACE MR0175 compliance.
■ Material Specifications (ASTM A193 B8MLN / B8MLNA)
| Material Type | Low-Carbon, Nitrogen-Strengthened, Molybdenum-Alloyed Austenitic Stainless Steel |
|---|---|
| UNS Number | S31653 |
| Corresponding Nut Grade | ASTM A194 Grade 8MLN (for B8MLN) / Grade 8MLNA (for B8MLNA) |
| Density | 8.00 g/cm³ (8,000 kg/m³) |
| Strengthening Mechanism | Interstitial Solid Solution Strengthening (Nitrogen offsets Carbon loss) |
| Magnetic Permeability | Non-Magnetic (B8MLNA) | Weakly Magnetic at thread roots (B8MLN Class 1) |
| Pitting Resistance (PREN) | 24.0 - 30.0 (Extremely high due to Molybdenum + Nitrogen synergy) |
■ Dimensions of Heavy Hex Bolts (ASME B18.2.1)
Standard dimensional specifications for ASME B18.2.1 Heavy Hex Bolts. The heavy hex profile provides the expanded bearing footprint necessary to distribute massive compressive loads securely across heavily welded flanged joints in offshore and chemical infrastructure.
| Nominal Size (in) | Threads per Inch (TPI) | Width Across Flats (Max) | Head Height (Max) | Width Across Corners (Min) |
|---|---|---|---|---|
| 1/2" | 13 | 0.875" | 0.344" | 0.969" |
| 5/8" | 11 | 1.062" | 0.422" | 1.175" |
| 3/4" | 10 | 1.250" | 0.500" | 1.383" |
| 7/8" | 9 | 1.438" | 0.578" | 1.589" |
| 1" | 8 | 1.625" | 0.656" | 1.796" |
| 1-1/8" | 8 (UN) | 1.812" | 0.734" | 2.002" |
| 1-1/4" | 8 (UN) | 2.000" | 0.812" | 2.209" |
| 1-1/2" | 8 (UN) | 2.375" | 0.969" | 2.622" |
| 2" | 8 (UN) | 3.125" | 1.281" | 3.449" |
■ Chemical Composition (per ASTM A193)
| Grade | C (Max) | Cr | Ni | Mo (Moly) | N (Nitrogen) | Mn (Max) | Si (Max) |
|---|---|---|---|---|---|---|---|
| B8MLN / B8MLNA (S31653) | 0.030% | 16.0 - 18.0% | 10.0 - 14.0% | 2.00 - 3.00% | 0.10 - 0.16% | 2.00% | 1.00% |
■ Mechanical Properties
| Grade / Class | Tensile Strength (Min) | Yield Strength (0.2% Offset) | Elongation | Reduction of Area | Max Hardness |
|---|---|---|---|---|---|
| B8MLN (Class 1) | 75,000 psi (515 MPa) | 30,000 psi (205 MPa) | 30% Min | 50% Min | 96 HRB (223 HBW) |
| B8MLNA (Class 1A) | 75,000 psi (515 MPa) | 30,000 psi (205 MPa) | 30% Min | 50% Min | 90 HRB (192 HBW) |
*Unlike Grade B8MN (which uses Nitrogen to push yield strength to 35 ksi), the Nitrogen in B8MLN is primarily used to restore the baseline yield firmly to 30 ksi, compensating for the severe physical weakening effect of the ultra-low carbon chemistry necessary for safe welding.
■ Applicable Standards & Specifications
| Application Type | Bolts & Studs | Nuts | Grade Designation |
|---|---|---|---|
| Marine Weldments / Custom Spools | ASTM A193 | ASTM A194 | B8MLN / 8MLN |
| NACE / Welded Offshore Platforms | ASTM A193 | ASTM A194 | B8MLNA / 8MLNA |
| Cryogenic Marine Assemblies | ASTM A320 | ASTM A194 | B8MLN / 8MLN |
■ The Engineering Synthesis: Solving the Marine Weld Trilemma
Offshore structural engineers face a complex "Trilemma" when specifying fasteners that must be permanently welded to marine pressure vessels: they need chloride resistance, high yield strength, and immunity to weld-decay.
Standard B8M (316) has the strength and chloride resistance, but will corrode rapidly in the heat-affected zone if welded. B8ML (316L) solves the weld-decay issue with low carbon, but physically weakens the bolt, causing it to fail strict ASME flange pressure tests due to inadequate yield strength. B8MN (316N) has the strength, but standard carbon levels mean it cannot be safely welded.
Grade B8MLN is the ultimate solution. It retains the pristine weldability of the "L" grade (zero sensitization), the marine survival of Molybdenum, and uses Nitrogen solid-solution strengthening to ensure the fastener maintains the robust 30 ksi yield limit. This allows engineers to safely arc-weld studs directly into offshore containment vessels without requiring a massive post-weld heat treatment furnace.
■ Fastener Types Available
| Fastener Category | Standard and Specialty Types Available | Primary Engineering Function |
|---|---|---|
| Marine Weld Studs | Weld Studs, Tap End Studs, Fully Threaded Spool Rods. | Designed to be permanently arc-welded into offshore housings and desalination vessels. |
| Heavy Industrial Fasteners | Heavy Hex Bolts, Hex Cap Screws, U-Bolts. | Standard cryogenic and petrochemical fastening requiring absolute sensitization immunity. |
| Matched Nuts (A194) | Heavy Hex Nuts (Grade 8MLN / 8MLNA). | Strictly matched chemistry prevents galvanic corrosion in severe saltwater environments. |
■ Commercial Supply Chain Dynamics: Why Choose Ananka
The global industrial fastener market requires manufacturing entities capable of blending hyper-scale production volume with microscopic precision. Ananka Fasteners exemplifies the apex of modern industrial hardware manufacturing, servicing over 240 high-value corporate clients spanning more than 40 countries.
- Stringent Global Certification: Ananka operates under an integrated management system certified to ISO 9001:2015, ISO 14001:2015, and ISO 45001:2018. We hold the prestigious PED 2014/68/EU certification for explosive, high-pressure environments.
- Exotic Alloy Mastery: Our deep expertise in highly engineered marine welding and cryogenic alloys extends far beyond 316LN; we actively forge and machine superalloys including Inconel 718, Hastelloy C276, Monel K500, and Titanium Grade 5.
- Customization and Capacity: Utilizing a strict 6-step in-house quality check protocol, we possess the agile manufacturing capacity to rapidly prototype, forge, anneal, test, and ship specialized fasteners globally.
■ Engineering FAQs
-
1. Is ASTM A193 B8MLNA compliant with NACE MR0175 for offshore sour gas?
Yes, flawlessly. The "A" designation guarantees a post-fabrication solution anneal, capping the hardness at a maximum of 90 HRB and removing all cold-working stress. Combined with the low-carbon chemistry and high molybdenum content, this makes B8MLNA exceptionally resistant to sulfide stress cracking (SSC) in offshore H2S environments. -
2. Does the addition of Nitrogen make the weld brittle?
No. In austenitic stainless steels like 316LN, Nitrogen acts as a strong austenite stabilizer. It actually refines the grain structure in the heat-affected zone during welding, improving both the mechanical toughness and localized corrosion resistance of the weldment. -
3. Can B8MLN be used in extreme cryogenic temperatures?
Absolutely. Austenitic stainless steels excel in sub-zero environments, and the addition of Nitrogen in B8MLN actively stabilizes the austenite phase even further. It resists brittle fracture transition, retaining massive impact toughness at temperatures plunging to -320°F (-196°C) for LNG marine transport applications.