Zeron 100 heavy hex bolts are super duplex stainless steel bolts (UNS S32760 / Werkstoff 1.4501) with the heavy hex pattern per ASME B18.2.6, ~12% wider across-flats and ~9% thicker under the head than standard hex bolts (B18.2.1). Used where a stud-and-nut assembly would normally go but the joint geometry forces a single-bolt solution: structural steel connections, flange clamps, valve-body bolting on heavy-wall pipe classes, and high-clamp-load offshore deck connections. The wider across-flats lets a torque wrench seat without socket spread, and the thicker head develops the full A1082 ultimate-tensile load through the bolt body without bearing-surface deformation under preload.
Wider across-flats + thicker head than standard hex · PREN ≥ 40 · Hardness ≤ 28 HRC · NORSOK M-650 + API 6A PSL3
Zeron 100 in heavy hex pattern is the right choice when the bolted joint sees high preload + corrosion + repeated maintenance access. Typical service: ASME B16.5 Class 1500 / 2500 flanges where stud bolts won't fit due to back-clearance, structural connections on FPSO deck modules, valve-body bonnet bolts on API 6D pipeline valves, and large-diameter manifold-stop bolts. We supply SA, FG, FLT, and AFP supply states, pick by yield envelope and service temperature.
| Thread | Heavy hex AF (in) | Heavy hex head height (in) | Standard hex AF (in) | Standard hex head height (in) |
|---|---|---|---|---|
| 1/2-13 UNC | 7/8 | 5/16 | 3/4 | 5/16 |
| 5/8-11 UNC | 1-1/16 | 25/64 | 15/16 | 25/64 |
| 3/4-10 UNC | 1-1/4 | 15/32 | 1-1/8 | 15/32 |
| 7/8-9 UNC | 1-7/16 | 35/64 | 1-5/16 | 35/64 |
| 1-8 UN | 1-5/8 | 39/64 | 1-1/2 | 39/64 |
| 1-1/4-8 UN | 2 | 25/32 | 1-7/8 | 25/32 |
| 1-1/2-8 UN | 2-3/8 | 15/16 | 2-1/4 | 15/16 |
| Standard | Coverage |
|---|---|
| ASME B18.2.6 | Heavy hex bolts (inch series), pattern dimensions, head height, across-flats |
| ASME B18.2.3.6M | Heavy hex bolts (metric series, M16-M48 typical) |
| ASTM A1082 | Stainless stud, bolt, screw, threaded rod, mechanical envelope for super duplex bolts |
| ASTM A479 / A276 | Stainless steel bars and shapes, source bar specs |
| ASME B1.1 / ISO 965 | Thread tolerance class 2A / 6g (loose fit, anti-galling) |
| NACE MR0175 / ISO 15156-3 | Sour-service hardness limit ≤ 28 HRC |
| NORSOK M-650 + M-630 MDS 055 | QTR'd manufacturer for North Sea topside heavy bolting |
| API 6A PSL 3 | Wellhead and tree equipment qualification |
| API 6D / 6DSS | Pipeline valves and subsea valves, valve-body heavy hex bolting |
| EN 10269 | European fastener spec for pressure equipment |
| Property | SA | FG | FLT |
|---|---|---|---|
| 0.2% Yield | 620-720 MPa | 700-800 MPa | 620-720 MPa |
| UTS | 800-870 MPa | 870-940 MPa | 800-870 MPa |
| Hardness body | 22-27 HRC | 24-28 HRC | 22-27 HRC |
| Hardness rolled root | 25-28 HRC | 26-28 HRC | 25-28 HRC |
| Charpy V-notch -46°C | 60-110 J | 50-90 J | 80-130 J |
| Ferrite | 40-52 % | 40-52 % | 38-48 % |
| CPT (G48 Method E) | ≥ 50°C | ≥ 50°C | ≥ 50°C |
| Service | Recommended supply state | Why heavy hex |
|---|---|---|
| ASME B16.5 Class 1500 / 2500 flange bolting | FG | Stud-and-nut blocked by back-clearance; single heavy hex bolt fits |
| API 6D pipeline valve body bonnet bolts | FG (NACE-controlled) | High clamp load + sour service + cyclic disassembly |
| FPSO deck module structural steel connection | SA or FG | Wider across-flats handles socket spread under high torque |
| Subsea manifold valve bonnet (API 6DSS) | FLT | Cold deepwater + cyclic install/recovery; Charpy reserve at -46°C |
| Heat exchanger floating-head closure bolts | SA | Repeated tube-bundle removal cycles; SA hot-headed cheaper |
| Compressor casing bonnet bolts (high-pressure offshore) | FG (NACE) | HPHT load envelope + sour |
| Repeated-makeup valve / flange high-torque service | AFP-coated FG | Coating prevents galling; predictable torque-to-tension |
When the joint geometry doesn't have back-clearance for nuts on both sides, or when single-side install access matters. Heavy hex bolts are the right choice on welded valve bonnets, structural connections to fixed plates, flange clamps where one side is buried, and any joint where a stud's protruding ends would interfere with adjacent equipment. Where back-clearance is available and disassembly happens through the studs, prefer studs + heavy hex nuts, lower cost, more thread engagement, and stud-and-nut handles thermal cycling better than a single bolt.
Heavy hex pattern adds thread-bearing area under the head and across-flats area for the wrench. Under high-clamp-load preload, standard hex head can deform locally at the bearing surface (the underside of the head) which relaxes preload. The heavy pattern's thicker head distributes the bearing load over more area. Wider across-flats also gives more torque-wrench engagement for the same socket size, reducing socket spread on rounded socket fits.
Yes, all standard coatings (Xylan, Xylar, SermaGard, Dacromet, MolyKote, TakeCoat) are applied per ASTM F1137 to heavy hex bolts on request. Add 5-7 working days lead time for fluoropolymer coatings, 7-10 days for metallic / ceramic. Coating cert ships alongside the base-bolt MTC.
Stock sizes (1/2", 5/8", 3/4", 1", 1-1/4", 1-1/2" UNC + M16-M48 metric) ship in 5-7 working days with 3.1 MTC, 10-14 days with witnessed 3.2 MTC. NORSOK M-650 QTR'd lots take 14-21 days. Specials cut from solution-annealed bar within 5 working days from RFQ approval.
Send the spec (size + length + thread + supply state + standards / MDS to comply with + coating if any + quantity + destination port) to info@torqbolt.com or +91-22-66157017 / WhatsApp.
