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 U-Bolts
From TorqBolt (Mumbai, India): Super Duplex 2507 U-bolts in UNS S32750 clamp pipes, conduit, and tubing in marine, offshore, and chemical-plant pipe-support systems. Bent-rod U-bolts are formed from solution-annealed S32750 round bar (ASTM A479) and post-form solution-annealed and water-quenched to restore the duplex microstructure. Two hex nuts and washers complete the assembly.
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 U-Bolts Size Range
U-bolts are offered in two bend profiles. Round bend matches pipe outside diameter; square bend matches square tubing or a beam flange. Thread diameter spans 1/4 inch through 1-1/4 inch UNC on the US series, and M6 through M30 on the metric series. Pipe-clamp round bend U-bolts are sized to NPS 1/2 through NPS 24, matching the outside diameter of standard schedule pipe per ASME B36.10M. Square bend U-bolts cover industrial square tubing from 25 mm to 200 mm. Working leg length is set per customer drawing at the quotation stage. Each U-bolt ships with two heavy hex nuts; a backing saddle clamp is available on request. Reference build: an NPS 6 round bend U-bolt in Super Duplex 2507 uses 5/8-11 UNC thread, 6.625 inch inner diameter, and a 12 inch leg.
| Bend Profile | Thread Range | Sized To |
|---|---|---|
| Round bend (pipe clamp) | 1/4 in. to 1-1/4 in. UNC; M6 to M30 | NPS 1/2 through NPS 24 per ASME B36.10M |
| Square bend (beam, tube, ductwork) | 1/4 in. to 1-1/4 in. UNC; M6 to M30 | Square tubing 25 mm to 200 mm |
| Reference build, NPS 6 round bend | 5/8-11 UNC | 6.625 in. inner diameter, 12 in. leg |
Super Duplex 2507 U-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) |
| Project drawing, ASME B1.1 / ISO 261 thread spec | 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 U-Bolts Applications
U-bolts in Super Duplex 2507 are specified for pipe restraint and exhaust mounting in chloride-laden environments where carbon steel and 316 fail by pitting or crevice attack within months. Typical scopes include seawater fire main brackets, deck-mounted ballast piping clamps on FPSO topside modules, exhaust uptake clamps on offshore gas turbine generator packages, and brine return line restraints on reverse osmosis desalination trains. Onshore, the same U-bolts hold FGD recirculation slurry pipework against absorber tower steel, where wet limestone chemistry combines low pH with chloride carry-over. Marine engine rooms use them on diesel and gas turbine exhaust runs, since the bend zone resists hot salt-laden condensate during cold starts.
- Seawater fire main brackets, deck-mounted ballast piping on FPSO topsides
- Exhaust uptake clamps, offshore gas turbine generator packages, marine engine room exhaust runs
- Brine return line restraints, reverse osmosis desalination trains, high-pressure membrane housings
- FGD recirculation slurry pipe supports, wet absorber towers handling chloride carry-over
- Oil and gas pipe restraint, manifold tie-downs, flowline anchor straps per API 20F
- Chemical processing, heat exchanger shell support clamps, reactor jacket pipework
Super Duplex 2507 U-Bolts FAQ
How do I size a round bend U-bolt for an NPS 4 schedule 80 pipe?
Pipe outside diameter for NPS 4 is 4.5 inch regardless of schedule, so the U-bolt inner diameter must be 4.5 inch plus 0.062 inch running clearance, giving a 4.562 inch nominal ID. Confirm against the pipe OD table in ASME B36.10M before release. Schedule changes wall thickness, not OD, so the same U-bolt fits schedule 40, 80, and 160 of the same NPS.
Round bend versus square bend, when do I use each?
Round bend wraps cylindrical sections: pipe, round tubing, conduit, and round duct. Square bend wraps flat-sided sections: I-beam flanges, channel webs, square or rectangular tubing, and rectangular ductwork. Mixing them, fitting a round bend over a square section or vice versa, leaves a point contact that gouges the coating and cracks the parent material under vibration.
Do you supply U-bolts with backing saddles?
Yes. Matching cast or rolled saddle clamps are available in Super Duplex 2507 on the same heat as the U-bolt, so the saddle, the U-bolt, and the nuts trace to one mill certificate. This satisfies single-heat traceability per NORSOK M-650 QTR and avoids galvanic mismatch between clamp and fastener in seawater service.
What is the torque sequence for U-bolt nuts?
Snug-tight both nuts hand-fast, then alternate diagonally across the U in 25 percent torque increments to the final value, repeating the cycle until no nut moves. For piping applications, follow ASME PCC-1 for the cross-pattern sequence and lubricant factor. Final torque depends on thread series, lubricant, and saddle stiffness; calculate from K factor 0.16 lubricated.
Are U-bolts heat-treated separately or with the parent bar?
Hot-bent at controlled temperature, then solution annealed at 1040 to 1100 degrees Celsius and water quenched, per NORSOK M-630. The bend zone is re-checked after annealing: ferrite must read 35 to 55 percent per WRC-1992 point-count, hardness must stay at or below 28 HRC for NACE service, and PMI is performed on each bend to confirm chemistry has not drifted from the parent bar.
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