Standards
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 925 Heavy Hex Bolts (UNS N09925)
Structural-grade heavy hex bolts ASME B18.2.6 / B18.2.3.6M — thicker head + larger AF than standard hex
Incoloy 925 heavy hex bolts (UNS N09925) are an upsized variant of the standard hex bolt with a thicker head and larger across-flats (AF) dimension. They are governed by ASME B18.2.6 (Fasteners for Use in Structural Applications) rather than ASME B18.2.1 (general hex bolts) and are the default head form for high-load structural-steel connections, pressure-vessel bolting and any joint requiring more wrench-engagement contact than a standard hex head provides. The "heavy" series gives a head that is typically 1/8" larger AF and 1/16" thicker than the standard hex equivalent, for example, a 1" diameter heavy hex has 1-5/8" AF (vs 1-1/2" for the standard hex) and 39/64" head height (vs 43/64"). TorqBolt manufactures Incoloy 925 heavy hex bolts in sizes 1/4" to 4" diameter (M6 to M64) in the solution-annealed and aged condition (per heat-treatment specification) with 100% hardness inspection ensuring the 35 HRC NACE MR0175 sour-service cap. Every order ships with EN 10204 3.1 manufacturer's MTC vs ASTM B805 requirements; 3.2 with TPI witness on request.
Need Incoloy 925 heavy hex bolts? Email info@torqbolt.com with diameter × length, thread reach (full or partial), thread series (UNC / 8UN / metric), quantity, applicable standards (ASME B18.2.6 vs B18.2.3.6M, NACE MR0175 stamp). WhatsApp +91-22-66157017.
Heavy Hex Bolt Variants Manufactured
| Variant | Description | Standard | Typical Use |
|---|---|---|---|
| Heavy hex bolt (partial thread) | Larger AF + thicker head than B18.2.1 hex bolt; plain shank below head + threaded tip | ASME B18.2.6 / B18.2.3.6M (metric) | Structural-steel bolted joints; bridges, towers, lattice frames |
| Heavy hex bolt (fully threaded) | Same head as above but threaded full length | ASME B18.2.6 / DIN 6914 | Adjustable-grip + tapped-hole structural connections |
| Heavy hex structural bolt (high-strength) | Tighter tolerance + chamfered point + washer face under head | ASTM A325 / F3125 equivalent in CRA | Pretensioned (TC bolt) joints in structural steel |
| Heavy hex bolt (HV / HR series) | European structural pattern; matched HV nut + HR washer | EN 14399 / DIN 6914 + 6915 + 6916 | European structural-steel bolted assemblies |
| Heavy hex flange bolt | Integral washer face under heavy hex head | ASME B18.2.1 / EN 1665 heavy | Vibration-prone heavy structural |
Standard Size Range & Across-Flats Dimensions
| Diameter | UNC (inch) / 8UN | Metric Coarse | Heavy AF (B18.2.6) | Heavy Head Height | Length Range |
|---|---|---|---|---|---|
| 1/4" / M6 | UNC 20 | M6 × 1.0 | 1/2" / 13 mm | 11/64" / 4 mm | 20 to 100 mm |
| 3/8" / M10 | UNC 16 | M10 × 1.5 | 11/16" / 17 mm | 15/64" / 7 mm | 25 to 150 mm |
| 1/2" / M12 | UNC 13 | M12 × 1.75 | 7/8" / 22 mm | 5/16" / 8 mm | 30 to 200 mm |
| 5/8" / M16 | UNC 11 | M16 × 2.0 | 1-1/16" / 27 mm | 25/64" / 10 mm | 40 to 300 mm |
| 3/4" / M20 | UNC 10 | M20 × 2.5 | 1-1/4" / 32 mm | 15/32" / 13 mm | 50 to 400 mm |
| 7/8" / M22 | UNC 9 | M22 × 2.5 | 1-7/16" / 36 mm | 35/64" / 14 mm | 50 to 450 mm |
| 1" / M24 | UNC 8 / 8UN | M24 × 3.0 | 1-5/8" / 41 mm | 39/64" / 16 mm | 60 to 500 mm |
| 1-1/8" / M30 | UNC 7 / 8UN | M30 × 3.5 | 1-13/16" / 46 mm | 11/16" / 18 mm | 75 to 500 mm |
| 1-1/4" / M33 | UNC 7 / 8UN | M33 × 3.5 | 2" / 50 mm | 3/4" / 20 mm | 75 to 600 mm |
| 1-3/8" / M36 | UNC 6 / 8UN | M36 × 4.0 | 2-3/16" / 55 mm | 27/32" / 22 mm | 100 to 600 mm |
| 1-1/2" / M39 | UNC 6 / 8UN | M39 × 4.0 | 2-3/8" / 60 mm | 15/16" / 24 mm | 100 to 700 mm |
| 1-3/4" / M45 | 8UN | M45 × 4.5 | 2-3/4" / 70 mm | 1-3/32" / 28 mm | 125 to 800 mm |
| 2" / M48 | 8UN | M48 × 5.0 | 3-1/8" / 75 mm | 1-7/32" / 31 mm | 150 to 900 mm |
| 2-1/2" / M56 | 8UN | M56 × 5.5 | 3-7/8" / 85 mm | 1-1/2" / 38 mm | 175 to 1000 mm |
| 3" / M64 | 8UN | M64 × 6.0 | 4-5/8" / 95 mm | 1-13/16" / 46 mm | 200 to 1200 mm |
| 4" | 8UN | 6" /. | 2-7/16" /. | 250 to 1500 mm |
Why heavy hex over standard hex? The larger AF gives a wider socket-engagement contact area, allowing higher torque without rounding the corners; the thicker head allows higher preload before head crushing or tearing. For high-load joints (preload > ~70% of bolt yield strength), heavy hex is the engineering default.
Mechanical Property Requirements
| Property | Aged Condition (ASTM B805 min) |
|---|---|
| Tensile Strength | 165 ksi (1140 MPa) min |
| 0.2% Yield Strength | 110 ksi (760 MPa) min |
| Elongation in 4D | 18% min |
| Reduction of Area | 25% min |
| Hardness | 32–35 HRC (NACE sour-service cap) |
| Charpy V-notch at -46°C | 40 J min (NACE sour service) |
For pretensioned structural-steel applications (TC bolt equivalent), the heavy hex bolt is calibrated to F3125 / A325 strength class, in Incoloy 925 the 110 ksi YS exceeds the F3125 Type 1 minimum (92 ksi YS) so the bolt is NEVER strength-limited.
Applicable Standards
- ASTM B805, UNS N09925 forging stock (input)
- ASME B18.2.6, Fasteners for Use in Structural Applications (heavy hex inch series)
- ASME B18.2.3.6M, Heavy Hex Bolts (metric)
- EN 14399 (parts 3, 4, 7, 8), High-Strength Structural Bolting Assemblies (HV / HR systems)
- DIN 6914 + 6915 + 6916, Heavy hex bolts + nuts + washers (German pattern)
- ASTM F3125, High-Strength Structural Bolts equivalent in CRA
- ASTM A325 / A490, structural strength class reference (Incoloy 925 exceeds both)
- API Specification 6A, Wellhead and Tree Equipment (PSL-1 to PSL-4)
- NACE MR0175 / ISO 15156-3, Table A.10 sour-service qualification
- NORSOK M-630 MDS A30, Norwegian Continental Shelf bolting
- EN 10204 3.1 / 3.2, certification
API 6A PSL Documentation Levels
| PSL | Pressure Class | Charpy | NDE |
|---|---|---|---|
| PSL-1 | 2,000–5,000 psi | Not required | Visual |
| PSL-2 | 5,000–10,000 psi | Not required | UT or MT |
| PSL-3 | 10,000–15,000 psi | 27 J at -29°C | 100% UT |
| PSL-3G | 10,000–15,000 psi gas | 27 J at -46°C / -101°C | 100% UT + grain size |
| PSL-4 | 15,000–20,000 psi | 40 J at -46°C | 100% UT + 100% MT + TPI |
Manufacturing Sequence
- Bar input: Incoloy 925 round bar per ASTM B805 in annealed condition. Larger starting diameter than standard hex bolt to give the heavier head AF after upset.
- Heavy-head upset forging: Hex head formed by cold or warm upset on a header press with custom heavy-series die. The larger AF + thicker head requires more material flow than a standard hex; warm upset (~1500°F) preferred for diameters above 3/4" to avoid die wear.
- Shank machining: Plain-shank diameter turned to nominal bolt size. Heavy hex bolts often have a shoulder under the head with a controlled fillet radius for fatigue resistance.
- Thread cutting / rolling: Threads applied in solution-annealed condition. Thread rolling preferred for fatigue-loaded structural service (residual compressive stress at root).
- Solution anneal + age cycle: Per heat-treatment specification, 1900°F WQ + 1365°F × 8h FC + 1150°F × 8h AC. The thicker head requires careful furnace loading to ensure uniform soak temperature.
- Final inspection: Heavy-hex head dimensional check (heavy AF, heavy head height, washer-face diameter); thread gauging Go / No-Go; 100% Rockwell hardness within 32–35 HRC; sample tensile + Charpy.
- Marking: Heavy-series identification mark on head face (typically "HH" or grade designation) plus heat number, UNS N09925, NACE stamp.
Companion Components
- Heavy hex nuts, matched companion ASME B18.2.4.6M / B18.2.6
- Heavy structural washers, F436 equivalent thickness in CRA
- DTI (direct-tension-indicator) washers, for pretensioned structural joints
- Thread compound, sulphur-free, copper-free anti-seize per API RP 7A1
Application Examples
- Structural-steel connections: Beam-to-column, splice plates, base plates in offshore structures (TLP topsides, jack-up legs)
- Pressure-vessel head bolting: Sour-service vessels with manway / inspection-port heavy bolted closures
- Heat exchanger channel cover bolts: Where higher preload is required than standard hex bolts can deliver
- Pump baseplate bolting: Sour-service centrifugal pumps with heavy mounting flanges
- Compressor frame bolts: Reciprocating sour-gas compressor base + frame connections
- Subsea structural connections: Mudline suspension, conductor housings, foundation hardware
- Topside structural fasteners: Equipment skids, pipe-rack supports, padeyes
- Wind-turbine tower bolting (offshore): Structural connections in chloride-rich marine atmosphere
Standard Coatings & Finishes
- Bare (passivated): Per ASTM A380 / A967, standard sour-service finish
- PTFE coating: Xylan 1424 / 1070, low-friction make-up for high-torque structural applications
- Phosphate + oil: MIL-DTL-16232 + light oil for storage protection
- Cad plate / hot-dip galvanise: NOT applied (Incoloy 925 is corrosion-resistant; coatings add galvanic / hydrogen-charging risk)
Frequently Asked Questions
What's the difference between a heavy hex bolt and a standard hex bolt? Heavy hex has larger across-flats (AF) and thicker head than standard hex bolt at the same nominal diameter. Example: 1" diameter heavy hex = 1-5/8" AF + 39/64" head height; 1" standard hex = 1-1/2" AF + 43/64" head height (head height comparison varies by series). The larger AF gives more wrench engagement and the thicker head allows higher preload without head crushing, critical for high-load structural and pressure bolting.
Are heavy hex bolts the same as A325 / A490 structural bolts? Dimensionally similar, A325 (now consolidated into ASTM F3125) heavy hex structural bolts use the same ASME B18.2.6 head dimensions. The difference is material grade: A325 is medium-carbon steel; A490 is alloy steel. Incoloy 925 heavy hex bolts are the corrosion-resistant equivalent and exceed both A325 and A490 strength minimums.
Can heavy hex bolts be supplied to EN 14399 (HV / HR system)? Yes, EN 14399 parts 3 (HR system: high-friction grip) and 4 (HV system: high-strength) define European structural bolting assemblies. We supply Incoloy 925 to the matched bolt + nut + washer set per EN 14399 for European projects. Specify HV vs HR, M-size, and length at RFQ stage.
What's the typical lead time for Incoloy 925 heavy hex bolts? Standard sizes (5/8" to 1" / M16 to M24): 5–7 weeks. Larger structural sizes (1-1/4" to 2"): 7–9 weeks. Custom heavy-series above 2" diameter: 10–14 weeks, reflects custom die setup for the heavy-head upset operation.
Why use heavy hex for sour service? Sour-service joints often require high preload to compress sealing gaskets reliably. The larger AF + thicker head of heavy hex tolerates this preload without head distortion, while keeping the whole assembly within the NACE 35 HRC sour-service envelope. It's a safety-margin engineering choice.
Documentation Package
- EN 10204 3.1 manufacturer's MTC (3.2 with TPI on request)
- Heat-lot chemistry vs UNS N09925 limits
- Tensile + RA + elongation per heat / per heat-treatment lot
- 100% hardness inspection (32–35 HRC NACE band)
- Charpy at -46°C / -101°C as applicable
- Heat-treatment furnace chart-recorder traces
- Heavy-hex head dimensional check ASME B18.2.6 / B18.2.3.6M
- Thread gauge inspection ASME B1.3
- NACE MR0175 Table A.10 reference
- API 6A PSL level reference (TPI for PSL-4)
- Bolt marking: heavy-series identifier + heat number + standard ref + NACE stamp
Related Products
- Heavy hex nuts, matched companion
- Standard hex bolts, standard AF + head height variant
- Hex cap screws, precision-tolerance variant
- Stud bolts, both-end-threaded for repeated-disassembly joints
- Washers, heavy structural F436 equivalent
- Full Incoloy 925 datasheet
Request a Quote
For Incoloy 925 heavy hex bolts with full MTC documentation:
- Email: info@torqbolt.com
- Phone: +91-22-66157017
- WhatsApp: +91-22-66157017
Specify diameter, length, thread reach, thread series (UNC / 8UN / metric), head dimensional standard (ASME B18.2.6 / B18.2.3.6M / EN 14399 / DIN 6914), quantity, applicable standards (API 6A PSL level, NACE MR0175 stamp, NORSOK MDS A30, ASTM F3125 strength class), required MTC level (3.1 / 3.2 with TPI witness) and any coating / finish requirement.
References: ASTM B805; ASME B18.2.6 (heavy hex inch); ASME B18.2.3.6M (heavy hex metric); EN 14399 parts 3, 4, 7, 8 (HV / HR structural bolting); DIN 6914 / 6915 / 6916 (heavy hex bolt + nut + washer); ASTM F3125 (high-strength structural bolts); ASTM A325 / A490 (legacy structural reference); ASME B1.1 / B1.13M (thread series); ASME B1.3 (thread gauging); API Specification 6A Annex M; NACE MR0175 / ISO 15156-3 Table A.10; NORSOK M-630 / M-650; EN 10204; ASTM A380 / A967. Special Metals Corporation INCOLOY® alloy 925 Technical Bulletin. INCOLOY® is a registered trademark of Special Metals Corporation.
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