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 Studs (UNS N09925)
Tap-end, continuous-thread, welding, double-end + interference-fit studs in nickel-iron-chromium alloy
Incoloy 925 studs (UNS N09925) is the broad fastener category encompassing all stud-type fasteners in this alloy, including the API 6A wellhead-spec stud bolts with a defined two-end thread pattern, plus tap-end studs (one threaded end + one engagement end), continuous-thread studs (analogous to a short threaded rod), welding studs (CD-stud or arc-welded), interference-fit studs, and double-end studs (Type 1 plain shank or Type 2 reduced shank). Studs differ from hex bolts in that they have no integral head, they are clamped between two nuts, or threaded into a tapped hole at one end, or welded to a substrate at one end. TorqBolt manufactures Incoloy 925 studs in M6 to M64 (1/4" to 4") sizes ASME B18.31.2 (double-end), AWS D1.6 (welding studs), DIN 938 / 939 / 940 (German tap-end studs), in the solution-annealed and aged condition (per heat-treatment specification) with 100% hardness inspection ensuring the 35 HRC NACE MR0175 sour-service cap.
Need Incoloy 925 studs? Email info@torqbolt.com with stud type (tap-end / continuous / welding / double-end), diameter × length, thread reach, quantity, applicable standards. WhatsApp +91-22-66157017.
Stud Variants Manufactured
| Variant | Description | Standard | Use |
|---|---|---|---|
| Stud bolt (full-thread, both-end accept nuts) | Threaded entire length; companion to two nuts | ASME B1.1 / stud-bolts page | API 6A wellhead, Christmas tree, BOP, flange bolting |
| Tap-end stud (engagement end + nut end) | Short engagement thread (typ 1.5d) + long nut-end thread; plain shoulder between | DIN 938 (engagement 1d), DIN 939 (1.25d), DIN 940 (2.5d) | Engine block, pressure-vessel jacket, tapped-hole bolting |
| Continuous-thread stud (short) | Threaded full length; lengths 25–500 mm (vs threaded rod >500 mm) | ASME B1.1 / DIN 976 | Short cut-to-length blank; flanged joints with non-standard length |
| Welding stud (CD, capacitor discharge) | Short stud welded to substrate by capacitor-discharge process | AWS D1.6 / ISO 13918 type CD | Sheet-metal attachment, instrument enclosure mounting on plate |
| Welding stud (arc / drawn-arc) | Larger stud welded by drawn-arc process with ferrule + arc shield | AWS D1.6 / ISO 13918 type DA | Structural attachment to thick plate, lug stand-offs, deck plates |
| Double-end stud (Type 1, plain shank) | Two threaded zones at ends, plain cylindrical shank between | ASME B18.31.2 Type 1 | Through-bolt joints with adjustable preload distribution |
| Double-end stud (Type 2, reduced shank) | Reduced-diameter shank distributing strain over a longer length | ASME B18.31.2 Type 2 | Fatigue-critical joints (BOP cyclic loading, subsea connectors) |
| Interference-fit stud | Engagement thread cut oversize for press-fit installation | Customer drawing | Permanent stud-and-tapped-hole installation |
Standard Size Range
| Diameter | UNC / 8UN | Metric Coarse | Length Range | Engagement Thread (DIN 939) |
|---|---|---|---|---|
| 1/4" / M6 | UNC 20 | M6 × 1.0 | 20 to 200 mm | 1.25 d = 7.5 mm |
| 3/8" / M10 | UNC 16 | M10 × 1.5 | 25 to 250 mm | 1.25 d = 12.5 mm |
| 1/2" / M12 | UNC 13 | M12 × 1.75 | 30 to 300 mm | 1.25 d = 15 mm |
| 5/8" / M16 | UNC 11 | M16 × 2.0 | 40 to 350 mm | 1.25 d = 20 mm |
| 3/4" / M20 | UNC 10 | M20 × 2.5 | 50 to 400 mm | 1.25 d = 25 mm |
| 1" / M24 | UNC 8 / 8UN | M24 × 3.0 | 50 to 500 mm | 1.25 d = 30 mm |
| 1-1/4" / M33 | UNC 7 / 8UN | M33 × 3.5 | 75 to 700 mm | 1.25 d = 41 mm |
| 1-1/2" / M39 | UNC 6 / 8UN | M39 × 4.0 | 100 to 900 mm | 1.25 d = 49 mm |
| 2" / M48 | 8UN | M48 × 5.0 | 150 to 1100 mm | 1.25 d = 60 mm |
| 3" / M64 | 8UN | M64 × 6.0 | 200 to 1300 mm | 1.25 d = 80 mm |
| 4" | 8UN | 250 to 1500 mm |
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 |
| Hardness | 32–35 HRC (NACE sour-service cap) |
| Charpy V-notch at -46°C | 40 J min (NACE sour service) |
Applicable Standards
- ASTM B805, UNS N09925 forging stock (input bar)
- ASME B18.31.2, Continuous and Double-End Studs (inch series)
- DIN 938 / 939 / 940, Tap-end studs, engagement-thread length 1d / 1.25d / 2.5d
- AWS D1.6, Structural Welding Code (stainless steel, includes nickel alloys for stud welding)
- ISO 13918, Welding studs (CD and DA types)
- ASTM A193 Grade B8N, Bolting Materials
- API 6A, Wellhead and Tree Equipment
- NACE MR0175 / ISO 15156-3, Table A.10 sour-service
- NORSOK M-630 MDS A30
- EN 10204 3.1 / 3.2, certification
Welding Stud Notes (CD & Drawn-Arc)
Welding studs in Incoloy 925 are a special case: the stud is welded to the substrate (rather than passing through a clearance hole), so the joint metallurgy depends on substrate compatibility. For Incoloy 925 stud welded to carbon-steel plate, the heat-affected zone on the carbon-steel side requires post-weld heat treatment if the substrate is in sour service. For Incoloy 925 stud welded to Incoloy 925 substrate, full post-weld solution anneal + age cycle is needed to recover joint strength, in practice this is rare; welded studs are typically used for non-pressure attachment service. See welding page for filler-metal selection and PWHT logic.
Manufacturing Sequence
- Bar input: Incoloy 925 round bar per ASTM B805 in annealed condition.
- Cut to length: Bar cut to stud length + thread allowance.
- End machining: Both ends faced, chamfered. For tap-end studs, the engagement end has a smaller chamfer than the nut end.
- Thread cutting / rolling: Threads applied in solution-annealed condition. Different thread reaches at each end for tap-end / double-end variants per applicable standard.
- Solution anneal + age cycle: Per heat-treatment specification.
- For welding studs: Tip preparation per AWS D1.6 (CD: precision tip + bonded flux pellet; DA: ferrule cup + flux pellet).
- Final inspection: Length, thread Go / No-Go, hardness, sample tensile / Charpy.
- Marking: Heat number + UNS N09925 + standard reference + NACE stamp.
Application Examples
- Wellhead / Christmas tree bolting: See stud bolts for the API 6A specific variant
- Engine block bolting (tap-end stud): Sour-service compressor cylinder block + crankcase
- Pressure-vessel jacket bolting: Tap-end stud into vessel jacket + nut on outside
- Subsea connector bolting (double-end Type 2): Reduced-shank for fatigue resistance
- Sheet-metal attachment (CD welding stud): Instrument enclosure / junction-box mounting
- Structural lug stand-offs (DA welding stud): Deck-plate / structural-plate attachment
- BOP cyclic-load bolting (double-end Type 2): Reduced-shank for cyclic-load fatigue life
- Cut-to-length stud manufacture: Continuous-thread short rod cut to job-specific lengths
Frequently Asked Questions
Is "studs" the same as "stud bolts"? Stud bolts are a SUBSET of studs, specifically, studs designed for use with two nuts in a flanged-joint configuration, typically per API 6A wellhead spec. The broader "studs" category includes tap-end (one threaded end engaged in tapped hole + one nut end), welding studs (one end welded to substrate), and continuous-thread studs (cut-to-length blanks). For API 6A wellhead service, see stud bolts.
What's the difference between DIN 938, DIN 939, and DIN 940 tap-end studs? All three are tap-end studs differing only in engagement-thread length: DIN 938 = 1d engagement (shortest, threads into thicker materials), DIN 939 = 1.25d engagement (most common, balanced for steel substrates), DIN 940 = 2.5d engagement (longest, for soft / aluminium substrates where more thread engagement is needed). Specify by DIN number at RFQ stage.
Can welding studs be used in sour service? Caution required, the welded joint creates a heat-affected zone (HAZ) that may exceed the NACE 35 HRC sour-service hardness cap unless post-weld heat-treated. For sour-service applications, prefer mechanically-fastened studs (tap-end, double-end, stud bolt + nut). Welding studs typically used for non-pressure attachment in sour atmosphere where the joint itself is not pressure-containing.
What's the typical lead time? Standard double-end / tap-end studs (M10 to M30 / 3/8" to 1-1/8"): 4–6 weeks. Larger sizes: 6–8 weeks. Welding studs (CD / DA): 8–10 weeks (low-volume specialty manufacture).
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)
- Sample Charpy at -46°C / -101°C
- Heat-treatment chart-recorder traces
- Length, engagement-thread length, nut-end thread length verification
- Thread Go / No-Go ASME B1.3
- NACE MR0175 Table A.10 reference
- Stud marking: heat number + UNS N09925 + standard ref + NACE stamp
Related Products
- Stud bolts, API 6A wellhead-spec stud variant
- Threaded rods, long-form continuous-thread rod for cut-to-length stud blanks
- Hex nuts + heavy hex nuts, mating nuts
- Washers, load distribution under nut bearing face
- Welding spec, for welding-stud applications
- Full Incoloy 925 datasheet
Request a Quote
For Incoloy 925 studs with full MTC documentation:
- Email: info@torqbolt.com
- Phone: +91-22-66157017
- WhatsApp: +91-22-66157017
Specify stud type (stud bolt / tap-end / continuous / welding / double-end Type 1 / Type 2 / interference-fit), diameter × length, thread reach (engagement-end length + nut-end length for tap-end variants), thread series, quantity, applicable standards (API 6A PSL / ASME B18.31.2 / DIN 938 / DIN 939 / DIN 940 / AWS D1.6), required MTC level (3.1 / 3.2 with TPI witness).
References: ASTM B805; ASME B18.31.2 (continuous + double-end studs); DIN 938 / 939 / 940 (tap-end studs); AWS D1.6 (welding code); ISO 13918 (welding studs CD + DA); ASTM A193 / F2281; 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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