Zeron 100 stud bolts are super duplex stainless steel studs (UNS S32760 / Werkstoff 1.4501) made from cold-drawn solution-annealed bar to ASTM A479 / A1082, threaded per ASME B1.1, and supplied with PMI & hardness verification on every heat. The 25Cr-7Ni-3.5Mo-0.7Cu-0.7W-0.25N composition gives PREN ≥ 40, the threshold for true super duplex behaviour, and the 50/50 austenite-ferrite microstructure delivers ~2× the yield of 316L while keeping seawater pitting and chloride-SCC resistance well above standard duplex 2205 (S31803).
Yield ≥ 550 MPa · Hardness ≤ 28 HRC · Charpy ≥ 45 J at -46°C
Where they earn their keep: NORSOK M-650 QTR'd offshore stud bolting, API 6A PSL 3 / 3G wellhead studs, sour-service NACE MR0175 / ISO 15156-3 hardness-controlled fasteners (HRC ≤ 28), FPSO topside flange bolting, subsea manifold studs, and seawater service across desalination + chemical processing trains. We supply SA, FG, FLT, and AFP supply states, one heat, one MTC, one mill-route, and you pick the supply state that matches your service envelope.
| Supply State | What it means | Yield (MPa, min) | Tensile (MPa, min) | Hardness (HRC, max) | Use case |
|---|---|---|---|---|---|
| SA | Solution Annealed (1100-1140°C, water quench) | 550 | 750 | 28 | Standard ASTM A479 stud bolts; default for non-aged super duplex |
| FG | Fastener Grade (lightly cold-drawn from SA) | 650 | 825 | 28 | NORSOK M-650 QTR'd, API 6A PSL3, sour-service flange bolting where SA yield is insufficient |
| FLT | Fasteners for Low Temperature (ASTM A320 L7 equivalent toughness) | 550 | 750 | 28 | LNG export terminals, FPSO topside arctic, ROV / subsea manifolds at ≤ -46°C |
We thread stud bolts continuously (full-thread per ASTM A1082) or as double-end studs (per ASME B16.5 flange standard). Every size is held in heat-tagged inventory; specials cut from solution-annealed bar within 5 working days for European / Middle East / Asian buyers.
| Series | Size range | Thread pitch | Length range | Standard |
|---|---|---|---|---|
| UNC (coarse) | 1/4 to 4 inch | 20 to 4 TPI | 1 to 36 inch | ASME B1.1, ASTM A1082 |
| UNF (fine) | 1/4 to 1-1/2 inch | 28 to 12 TPI | 1 to 24 inch | ASME B1.1, ASTM A1082 |
| 8UN (heavy) | 1 to 4 inch | 8 TPI | 4 to 36 inch | ASME B1.1, ASTM A1082 |
| Metric coarse | M6 to M100 | 1.0 to 6.0 mm | 25 to 1000 mm | ISO 261, ASTM A1082 |
| Metric fine | M8 to M64 | 1.0 to 4.0 mm | 25 to 600 mm | ISO 261, ASTM A1082 |
| Standard | What it covers | Why it matters for stud bolts |
|---|---|---|
| ASTM A1082 | Stainless steel stud, bolt, screw, and threaded rod | The fastener-spec home for super duplex studs, replaces older A193 references for S32760 service |
| ASTM A479 | Stainless steel bars and shapes | Source bar spec; mechanical envelope, ferrite content, intergranular-corrosion test |
| ASTM A276 | Stainless steel bars and shapes (alt) | Used in some buyer specs for cold-finished bar source |
| ASME B1.1 | Unified inch screw threads | UNC / UNF / 8UN thread form, allowance, tolerance class 2A/3A |
| ASME B16.5 | Pipe flanges and flanged fittings | Stud-bolt length tables for ANSI flange classes 150 / 300 / 600 / 900 / 1500 / 2500 |
| NORSOK M-650 | Qualification of manufacturers of special materials | TorqBolt's QTR scope covers 25Cr super duplex stud bolts, required for North Sea / Equinor / Aker BP work |
| NORSOK M-630 / MDS 055 | Material data sheet for super duplex SS | Defines acceptance criteria (composition, ferrite 35-55%, hardness, Charpy) |
| NACE MR0175 / ISO 15156-3 | Sour-service hardness limits | Stud bolts ≤ 28 HRC for H2S exposure; we measure rolled-thread + body |
| API 6A PSL 3 / 3G | Wellhead and Christmas tree equipment | Stud-bolt material qualification + impact testing for high-pressure upstream service |
| API 20E | Alloy and CRA steel bolting | Mill-test + traceability requirements per BSL-3 (Bolting Specification Level) |
| EN 10269 | Steels and nickel alloys for fasteners | European pressure-equipment buyers (PED 2014/68/EC) reference |
All values are the per-heat MTC range we hold internally; all are above ASTM A479 minimums. Hardness is rolled-thread root, measured with a converted Vickers reading after thread rolling (cold-work in the root raises local hardness 3-5 HRC vs body, we measure both and bracket the higher one against MR0175).
| Property | SA (typical) | FG (typical) | FLT (typical) | Test method |
|---|---|---|---|---|
| 0.2% Yield Strength | 620-720 MPa | 700-800 MPa | 620-720 MPa | ASTM A370 |
| Ultimate Tensile | 800-870 MPa | 870-940 MPa | 800-870 MPa | ASTM A370 |
| Elongation | 30-38 % | 25-32 % | 30-38 % | ASTM A370 |
| Hardness (body) | 22-27 HRC | 24-28 HRC | 22-27 HRC | ASTM E18 |
| Hardness (rolled root) | 25-28 HRC | 26-28 HRC | 25-28 HRC | ASTM E18 converted from HV |
| Charpy V-notch @ -46°C | 60-110 J | 50-90 J | 80-130 J | ASTM E23 |
| Ferrite content | 40-52 % | 40-52 % | 40-52 % | ASTM E562 / EN ISO 8249 |
| CPT (G48 Method E) | ≥ 50°C | ≥ 50°C | ≥ 50°C | ASTM G48-E (24 hr, 6% FeCl3) |
| Sigma-phase (A923 Method C) | Pass | Pass | Pass | ASTM A923 Method C (60 J min at room temp) |
| Industry & service | Recommended supply state | Why |
|---|---|---|
| North Sea topside flange bolting (NORSOK M-650 mandatory) | FG | Cold-work uplift gets to A193 B7-equivalent yield while staying NACE 28 HRC |
| API 6A wellhead studs, sour-service H2S exposure | FG (NACE-controlled) | PSL 3 impact testing + hardness witness traceable to PMI per heat |
| Subsea manifold / jumper / spool bolting | FLT | Charpy at -46°C exceeds 45 J; cold environment service |
| FPSO turret / swivel / mooring fasteners | FLT or AFP-coated FG | Cyclic loading + repeated-makeup, coating prevents galling on duplex threads |
| LNG export terminal cryogenic flanges | FLT | L7-equivalent low-temp toughness; matches A320 L7 buyer specs without using carbon steel |
| Desalination RO membrane vessel + brine line bolting | SA | Seawater + concentrated brine; PREN ≥ 40 + 0.7Cu addition |
| Chemical processing, HCl, H2SO4, dilute organic acid bolting | SA | Cu+W content gives reducing-acid resistance superior to 2507 |
| FGD scrubber + chimney bolting | SA or AFP-coated | Wet-flue-gas chloride + sulfate; AFP for periodic disassembly |
| Repeated-makeup high-torque flanges (galling risk) | AFP (Xylan / SermaGard / Dacromet) | Coating reduces friction coefficient from ~0.30 to ~0.10, makes torque-to-tension predictable |
Every Zeron 100 stud-bolt order ships with an EN 10204 type 3.1 (in-house QC) or 3.2 (third-party witnessed by TUV / BV / DNV / Lloyd's / ABS) certificate, depending on buyer spec. The cert is heat-traceable end-to-end, mill heat number flows through bar receipt, threading, NDT, and packing. PMI (positive material identification) is run on 100% of finished studs against a calibrated S32760 master, and the certificate stack includes:
Duplex-on-duplex threads gall. The same nitrogen-stabilised microstructure that gives Zeron 100 its strength also makes the rolled-thread surface energetic; under high torque, two duplex contact surfaces will weld-and-tear at the asperity level and seize. The fix is a low-friction coating system, the AFP supply state, applied per ASTM F1137. Standard options:
| Coating | Typical μ (steel-on-steel) | Service envelope | Best for |
|---|---|---|---|
| Xylan 1014 / 1070 / 1400 / 1424 | 0.10-0.13 | -50 to +260°C | Standard offshore + onshore sour service; blue, black, grey colours |
| Xylar 2 / 101 | 0.08-0.10 | -65 to +260°C | High-cycle, high-load (subsea, ROV-installable) |
| SermaGard 1105 / 1280 | 0.10-0.14 | -50 to +540°C | High-temp + corrosion combo; FGD, geothermal, refinery |
| Dacromet 320 / 500 | 0.10-0.13 | -40 to +300°C | Cathodic-protection-friendly; subsea + offshore primary fasteners |
| TakeCoat 1000 (ceramic) | 0.08-0.12 | up to +1100°C | High-temp specialty; geothermal wellhead, fired equipment |
| MolyKote | 0.08-0.10 | -70 to +450°C | High-pressure flange repeat-makeup, cryogenic LNG service |
No, they're a separate spec. ASTM A1082 is the home for stainless stud bolts including S32760 super duplex. B7M is for AISI 4140 quenched-and-tempered alloy steel. The two have similar yield envelopes (FG Zeron 100 hits A193 B7 levels in tensile) but completely different corrosion behaviour. Use Zeron 100 / A1082 when seawater, sour service, or chloride pitting is in play; B7/B7M when none of those apply.
NACE MR0175 / ISO 15156-3 sets 28 HRC as the cold-worked super duplex (S32760) hardness ceiling for sour service. The 22 HRC ceiling applies only to alloy steel (AISI 4140 / B7M family) where temper-embrittlement and HE susceptibility are different. Zeron 100 has its own annex (Table B.5) in ISO 15156-3 with the 28 HRC limit.
In most service envelopes, yes, drop-in. The 0.7% W and 0.7% Cu in Zeron 100 add reducing-acid resistance over SAF 2507 (which has neither). For pure-seawater use both perform equivalently (PREN both 41+). For HCl / H2SO4 wash-down service, Zeron 100 has the edge. Both qualify against the same NORSOK M-630 MDS 055 acceptance criteria.
M16, M20, M24, M30, M36, 5/8", 3/4", 7/8", 1", 1-1/4", and 1-1/2" UNC are kept in stock in 1m / 3m / 6m bar lengths; standard ANSI flange-class lengths (per ASME B16.5) are cut from these. Anything outside that range is cut from solution-annealed bar within 5 working days. Specials with non-standard length-to-diameter ratios (e.g. very long studs for large-OD subsea connectors) need PMA (Pre-Manufacturing Approval) drawing review.
Rolled threads cold-work the root and crest, raising local hardness 3-5 HRC over the body. We measure both: a body Rockwell C reading on a polished cross-section, and a Vickers HV reading at the rolled-thread root converted per ASTM E140 to HRC. NACE MR0175 compliance is judged against the higher of the two readings (typically the rolled root). All values reported on the MTC.
Stock sizes ship in 5-7 working days with 3.1 MTC, 10-14 working days with witnessed 3.2 MTC. NORSOK M-650 QTR'd lots with full Annex C documentation typically take 14-21 working days because of the third-party witness scheduling. PMA drawing approval (when required) adds 5-10 working days on the front end. RFQ via contact form or info@torqbolt.com, reply within one business day in Mumbai time (IST, UTC+5:30).
Send the spec (size + length + supply state + standards / MDS to comply with + quantity + destination port) to info@torqbolt.com or +91-22-66157017 / WhatsApp. We reply with stock availability, mill route, lead time, MTC tier, and price within one business day.
