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 Heavy Hex Bolts
From TorqBolt (Mumbai, India): Super Duplex 2507 heavy hex bolts in UNS S32750 use the larger heavy-hex head pattern per ASME B18.2.1 for high-load flange and structural connections. Material conforms to ASTM A1082 / API 20F. Heavy hex pattern provides greater bearing area and higher tightening torque capability vs standard hex.
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 Heavy Hex Bolts Size Range
TorqBolt manufactures heavy hex bolts to the ASME B18.2.1 heavy series, inch 1/4 through 1-1/2 inch. Heavy hex tops out at 1-1/2 inch by convention; above that the joint should move to a stud bolt with two heavy hex nuts (Super Duplex 2507 stud bolts). The defining feature of the heavy series is the across-flats dimension: it is one wrench size larger than a finished hex bolt of the same diameter. As an example, a 1/2 inch diameter heavy hex bolt takes a 7/8 inch wrench, versus 3/4 inch on a finished hex of equal nominal diameter. The head height is also taller, giving more bearing area and more meat for repeated wrench engagement. Threading is UNC coarse to ASME B1.1 through 1 inch, and 8UN above 1 inch. Lengths run 3/4 inch through 10 inch in stock; longer runs cut to order. Metric coverage is M12 through M36 with the corresponding heavier head dimensions per ISO 7411. Sour-service orders default to NACE MR0175 hardness, 28 HRC max.
| Nominal Diameter | Heavy Hex Across Flats | Thread Series |
|---|---|---|
| 1/4 in | 1/2 in | UNC (20 TPI) |
| 3/8 in | 11/16 in | UNC (16 TPI) |
| 1/2 in | 7/8 in | UNC (13 TPI) |
| 5/8 in | 1-1/16 in | UNC (11 TPI) |
| 3/4 in | 1-1/4 in | UNC (10 TPI) |
| 7/8 in | 1-7/16 in | UNC (9 TPI) |
| 1 in | 1-5/8 in | UNC (8 TPI) |
| 1-1/8 in | 1-13/16 in | 8UN |
| 1-1/4 in | 2 in | 8UN |
| 1-3/8 in | 2-3/16 in | 8UN |
| 1-1/2 in | 2-3/8 in | 8UN |
| M12 | 21 mm | ISO coarse |
| M16 | 27 mm | ISO coarse |
| M20 | 34 mm | ISO coarse |
| M24 | 41 mm | ISO coarse |
| M30 | 50 mm | ISO coarse |
| M36 | 60 mm | ISO coarse |
Super Duplex 2507 Heavy 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 (heavy hex) | 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 Heavy Hex Bolts Applications
Heavy hex bolts are specified by the engineering drawing where the head itself must take real abuse, either repeated wrench engagement during hot bolting or impact loading from shock and vibration. In our build mix the dominant uses are large structural connections in field-erected oil and gas vessels and skid frames, hot-bolting on flanged steam piping where the bolt is torqued under load and the wrench is hammered onto the head, anchor connections through baseplate doublers on rotating equipment, heavy machinery mounting where shock loads transfer through the head before reaching the threads, and structural steel cross bracing on offshore jacket nodes. Project specifications on FPSO topsides, desalination plant intakes, and FGD scrubber modules also default to heavy hex on accessible joints where the maintenance crew needs the larger wrench engagement for in-service tightening checks.
- Oil and gas surface facilities, field-erected vessel saddle bolting, manifold skid frames, flare stack base flanges
- Offshore jacket nodes, cross-bracing splice plates, conductor guide brackets, riser clamp connections
- Hot bolting on steam piping, in-service flange tightening where wrench is hammer-struck during torque cycles
- Desalination intake structures, sea-chest doubler plate bolting, screen frame mounting in brine spray
- FGD scrubber modules, absorber tower platform bracket bolting, ducting support frame connections
- Rotating equipment anchors, baseplate doubler bolting on pumps and compressors transmitting shock through the head
Super Duplex 2507 Heavy Hex Bolts FAQ
When does my specification call for heavy hex instead of finished hex?
Three triggers in our experience. First, wrench access: the larger across-flats gives the field crew a one-wrench-size bigger socket window, which matters in congested skid bays where a thin-wall finished hex socket will not seat properly. Second, impact loading: heavy machinery anchors, offshore jacket nodes, and any joint that sees shock during operation should take the head abuse on the heavier section. Third, hot bolting: when the wrench is hammer-struck during in-service torque cycles on steam piping, the heavy head resists rounding and the bolt survives multiple retorque events.
Can heavy hex bolts replace stud bolts on ASME B16.5 flanges?
Mechanically yes, practically discouraged. The head limits joint disassembly because it must be unscrewed clear of the flange face during break-out, whereas a stud bolt with two heavy hex nuts releases by backing off either nut. On any flange that will be opened for maintenance, gasket replacement, or in-line inspection, the stud is the correct part. Heavy hex on flange duty is reserved for permanent connections such as blind-end caps or weld-prep transition bolting where the joint is not designed to be reopened.
What is the across-flats difference between heavy hex and finished hex for the same diameter?
One wrench size larger on the heavy series. A 1/2 inch finished hex takes a 3/4 inch wrench; the 1/2 inch heavy hex takes 7/8 inch. A 3/4 inch finished hex takes 1-1/8 inch; the 3/4 inch heavy hex takes 1-1/4 inch. The pattern holds through the entire ASME B18.2.1 range and is the single dimensional feature that separates the two series. Head height is also greater on the heavy hex, giving more bearing area against the work and more thickness for impact resistance.
Why is 1-1/2 inch the practical upper limit for heavy hex?
Above 1-1/2 inch the head dimensions become unwieldy. A 1-3/4 inch heavy hex would call for an across-flats near 2-3/4 inch and a head height that interferes with adjacent bolting on standard flange bolt circles. The industry convention is to switch to a stud bolt with two heavy hex nuts at that point: same load path, lower head profile on each side, and the joint opens by backing off either nut rather than rotating a large bolt head. ASME B18.2.1 itself extends to 4 inch on the heavy hex pattern, but mill-stock availability and field practice both drop off sharply above 1-1/2 inch.
Are heavy hex bolts in Super Duplex 2507 cold-headed or hot-forged?
TorqBolt practice: cold forging up to M24 / 1 inch where the bar stock can be upset on the header without exceeding mill tooling limits, hot forging above that size. Super Duplex 2507 work hardens aggressively, so even cold-headed bolts go through a full solution anneal at 1040 to 1100 degrees Celsius (NORSOK M-630 window) followed by a water quench, never an air cool. Ferrite content is then verified on each heat at 35 to 55 percent base metal per ASTM E562 point count, with the QTR record cross-referenced to the heat number on the mill test certificate.
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