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
Super Duplex 2507 Hex Bolts
From TorqBolt (Mumbai, India): Super Duplex 2507 hex bolts in UNS S32750 follow ASME B18.2.1 (Square and Hex Bolts and Screws Inch Series) for inch-series or ISO 4014 / 4017 for metric-series dimensions. Material conforms to ASTM A1082 (and API 20F for oil/gas). Standard finish is solution annealed and water quenched; hardness 28 HRC max for NACE MR0175 compliance.
The dedicated standard for super duplex bolting is ASTM A1082/A1082M (high-strength precipitation hardening and duplex stainless steel bolting material), supplemented by API 20F for corrosion-resistant bolting in petroleum and natural gas service. TorqBolt manufactures under WPS qualified to NORSOK M-650 at the Mumbai facility, with hardness restricted to 28 HRC max for NACE MR0175 / ISO 15156-3 sour-service compliance.
Super Duplex 2507 Hex Bolts Size Range
We machine Super Duplex 2507 hex bolts to ASME B18.2.1 finished hex series (the lighter across-flats pattern, not heavy hex). Inch range runs 1/4-20 UNC through 1.5-6 UNC in lengths from 1/2 inch up to 8 inches. Metric range covers M5 through M48 in lengths from 10 mm up to 200 mm. Thread length follows the B18.2.1 rule: twice the bolt diameter plus 6 mm for lengths under 125 mm, twice the diameter plus 12 mm for longer bolts. The finished hex across-flats is narrower and the head is shorter than a heavy hex bolt of the same diameter, which keeps weight down on bracketry and machinery duty where a B16.5 raised-face flange is not involved. Raw stock is ASTM A479 S32750 bar to the chemistry locked at A1082.
| Diameter | Thread length per ASME B18.2.1 | Max bolt length |
|---|---|---|
| 1/4-20 UNC | 2D + 6 mm under 125 mm | 4 inches |
| 3/8-16 UNC | 2D + 6 mm under 125 mm | 5 inches |
| 1/2-13 UNC | 2D + 6 mm under 125 mm | 6 inches |
| 5/8-11 UNC | 2D + 6 mm under 125 mm | 6 inches |
| 3/4-10 UNC | 2D + 12 mm at and above 125 mm | 8 inches |
| 7/8-9 UNC | 2D + 12 mm at and above 125 mm | 8 inches |
| 1-8 UNC | 2D + 12 mm at and above 125 mm | 8 inches |
| 1.25-7 UNC | 2D + 12 mm at and above 125 mm | 8 inches |
| 1.5-6 UNC | 2D + 12 mm at and above 125 mm | 8 inches |
| M5 to M12 | 2D + 6 mm under 125 mm | 80 mm |
| M14 to M24 | 2D + 6 mm under 125 mm | 150 mm |
| M27 to M48 | 2D + 12 mm at and above 125 mm | 200 mm |
Super Duplex 2507 Hex Bolts Standards
| Standard | Scope |
|---|---|
| ASTM A1082 / A1082M | Dedicated standard, High-Strength Precipitation Hardening and Duplex Stainless Steel Bolting Material. Covers UNS S32750 (Type 2507) explicitly. |
| API 20F | Corrosion-Resistant Bolting for Petroleum and Natural Gas Industries (BSL-2, BSL-3) |
| ASTM A962/A962M | General requirements for stainless steel bolting (A1082 §1.2 companion) |
| ASTM A479 | Bar stock chemistry and properties (raw stock for machining) |
| ASTM A276 | Bar and shapes (alternate raw stock) |
| ASME B18.2.1, ISO 4014 / 4017 | Dimensional specification |
| ASME B1.1 / ISO 261 | Inch / metric thread call-outs |
| NORSOK L-005 | Compact flange connections (NCS reference) |
| NORSOK M-630 | Material data sheet (MDS D55, D57) |
| NORSOK M-650 | Manufacturer qualification (QTR) |
| NACE MR0175 / ISO 15156-3 | Sour-service compliance, 28 HRC max |
| API 6A PSL 3 / 3G | Wellhead and christmas tree fasteners |
| API 17D | Subsea wellhead and tree fasteners |
Super Duplex 2507 Mechanical Properties (per ASTM A1082)
| Property | Minimum | Typical |
|---|---|---|
| Tensile strength | 800 MPa (116 ksi) for ≤ 2 in. / 760 MPa (110 ksi) for > 2 in. | 800 to 1000 MPa |
| Yield strength (0.2 percent offset) | 550 MPa (80 ksi) for ≤ 2 in. / 515 MPa (75 ksi) for > 2 in. | 620 to 720 MPa |
| Elongation in 4D | 15 percent | 25 to 35 percent |
| Reduction of area | 33 percent | 40 percent |
| Hardness (A1082) | 310 HBN max | 250 to 300 HBN |
| Hardness (NACE sour-service) | 28 HRC max | 25 to 28 HRC |
| Charpy V-notch at minus 46 degrees Celsius | 45 J min | 60 to 100 J |
| PREN | 40 min | 41 to 43 |
Heat Treatment
Solution annealing at 1025 to 1125 degrees Celsius per A1082 (NORSOK M-630 narrows to 1040 to 1100 degrees Celsius), followed by rapid water quench. There is no aging or precipitation hardening; strength comes from the duplex austenite-ferrite microstructure itself. Final hardness check confirms 28 HRC maximum for NACE MR0175 compliance.
Super Duplex 2507 Chemistry per ASTM A1082
| Element | A1082 Min % | A1082 Max % |
|---|---|---|
| Carbon | (no min) | 0.030 |
| Manganese | (no min) | 1.20 |
| Phosphorus | (no min) | 0.035 |
| Sulfur | (no min) | 0.020 |
| Silicon | (no min) | 0.80 |
| Chromium | 24.0 | 26.0 |
| Nickel | 6.0 | 8.0 |
| Molybdenum | 3.0 | 5.0 |
| Nitrogen | 0.24 | 0.32 |
| Copper | 0.50 max, residual, not intentional | |
Companion Products
All companion components in matching UNS S32750 chemistry per A1082.
- Bolts, A1082 in S32750
- Stud bolts, A1082 in S32750, ASME B18.31.2
- Heavy hex nuts, A1082 in S32750, 8MA pattern
- Flat washers, UNS S32750, F436 dimensional pattern by special order
- Mating flanges, ASTM A182 F53
Super Duplex 2507 Hex Bolts Applications
Hex bolts are a general-purpose structural fastener, not a flange-joint fastener. On ASME B16.5 raised-face gasketed flanges we always specify stud bolts with 2H heavy hex nuts in Super Duplex 2507, because the double-threaded stud lets the operator tension or torque from either end, distributes load more evenly across the gasket, and accepts the calibrated procedures written for ASME PCC-1. Hex bolts do not.
Where we do specify Super Duplex 2507 hex bolts is the non-gasketed structural duty around the same platforms and plants: machinery foundations, pump and compressor baseplates and housings, valve actuator brackets, exchanger saddle bolting, tank skirt anchor bolts, ladder and walkway brackets, instrument enclosures bolted to deck steel on offshore platforms, NEMA-rated junction box covers exposed to chloride aerosol, cable-tray supports in splash zones, and access-panel hardware on subsea modules. The 2507 chemistry (Cr 24-26, Mo 3-5, N 0.24-0.32, PREN ≥ 40 per the PREN calculation) carries these joints through chloride pitting, crevice corrosion under washers, and the deck-wash hose-down cycle that destroys 316 and 904L in months.
- Marine and offshore, deck machinery foundations, instrument enclosures, NEMA junction boxes in chloride atmosphere
- Seawater service, pump and compressor baseplate bolting, sea-chest cover plate hardware, fire-water skid framing
- Desalination, high-pressure pump housing bolts, RO skid frame, brine pipework support brackets
- FGD, absorber tower walkway bracket bolting, ladder rungs, instrument tap supports in chloride flue-gas zone
- Chemical processing, exchanger saddle hold-down bolts, agitator gearbox mounting, valve actuator brackets
- Oil and gas surface facilities, separator skid hardware, tank skirt anchors, walkway and grating fixings
Super Duplex 2507 Hex Bolts FAQ
When should I specify hex bolts instead of stud bolts on duplex flanges?
On ASME B16.5 raised-face flange joints, never. We always specify stud bolts with two 2H heavy hex nuts on duplex pressure flanges. Studs win for three reasons. First, the joint procedure (ASME PCC-1) is written for studs because the operator can tension or torque from either end, which keeps gasket load uniform. Second, a stud bolt with a heavy hex nut presents a larger nut bearing surface to the flange face, so contact stress is lower and galling risk drops. Third, replacement of a stud is straightforward; replacement of a corroded hex bolt frozen in a tapped flange almost always means re-machining the flange. Hex bolts belong on structural duty: brackets, baseplates, machinery foundations, junction boxes, and cover plates that are not gasketed pressure-retaining joints.
What is the difference between a hex bolt (ASME B18.2.1) and a heavy hex bolt?
Both are six-sided externally threaded fasteners, but their head geometry is different. A finished hex bolt to ASME B18.2.1 has a smaller across-flats and a shorter head height than the heavy hex equivalent of the same nominal diameter. Worked example at 3/4 inch: finished hex is 1-1/8 inch across-flats and roughly 1/2 inch head height; heavy hex is 1-1/4 inch across-flats and roughly 15/32 inch head height with a thicker bearing washer face. Heavy hex is the pattern used on B16.5 flange bolting and on structural connections where wrench engagement and bearing area matter. Finished hex is the lighter general-purpose pattern for brackets and machinery foundations.
Can hex bolts be torqued or do they need tensioning?
Hex bolts are torqued. The published torque table for ASTM A193 B7 (and the equivalent procedure for Super Duplex 2507 in A1082) is the working starting point, with the friction coefficient adjusted for the coating (Xylan 1070 sits around 0.10, plain finish around 0.15). For non-gasketed structural joints, torque control with a calibrated wrench is the normal method. Hydraulic tensioning is rarely required on hex bolts because they are not used on the high-stiffness gasketed flange joints that demand uniform residual load. If a job calls for tensioning, the joint is almost always a stud bolt joint, not a hex bolt joint.
What thread series is used for inch hex bolts in Super Duplex 2507?
UNC (Unified Coarse) is our standard for inch Super Duplex 2507 hex bolts, cut to ASME B1.1 with class 2A external thread fit. UNRC (radius root) and UNF (fine) are available on request where the joint procedure calls for them, typically vibration-sensitive instrumentation hardware or thin-walled tapped housings. Metric thread to ISO 261 (coarse pitch) is also available on request across the M5 to M48 range. All inch thread call-outs reference ASTM A479 bar chemistry; thread cutting is done after solution anneal so the work-hardened thread root sits at the same hardness as the body.
Are the hex bolts heat-treated separately from stud bolts?
Yes. Hex bolts and stud bolts run in separate solution-anneal batches because the cross-section per piece is different and the load on the furnace differs. We size each batch so the centre of the largest piece in the load reaches the A1082 solution-anneal temperature band (1025 to 1125 degrees Celsius, NORSOK M-630 narrows to 1040 to 1100) for the soak time the section thickness requires, then water-quench inside the 3-minute window that pins ferrite content at 35 to 55 percent (WRC-1992 method, the bolting-material window). Mixing hex bolts and stud bolts in one furnace load risks an under-soaked stud or an over-soaked hex bolt; we do not do it. Each batch carries its own ferrite count, hardness check, and G48 Method E CPT result on the heat-traceable coupon.
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