Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Durehete Nuts — Alloy T41 / T31 / T22 (EN 10269 Cr-Mo-V Bolting Steel)
Durehete nuts are produced as hex pattern (ASME B18.2.2 / ISO 4032) and heavy-hex pattern (ASME B18.2.2 heavy series). Same Q+T heat lineage as the matching bolts; supplied as a matched set with traceability back to the same EN 10269 heat number where the procurement specification calls for matched bolting.
Durehete Grade Selection for Nuts
| Grade | Alloy | Werkstoff | EN 10269 designation | Service ceiling |
|---|---|---|---|---|
| Durehete 1055 | T41 | 1.7729 | 20CrMoVTiB4-10 | 565°C |
| Durehete 950 | T31 | 1.7711 | 40CrMoV4-6 | 540°C |
| Durehete 900 | T22 | — | 42CrMoV5-6 | 500°C |
Manufacturing Route
Nuts are custom-machined from EN 10269 bar stock at TorqBolt. The bar arrives in the quenched-and-tempered condition (austenitise 970-1010°C, oil or water quench, temper 660-730°C minimum 2 hours air cool). Threading, head forming and finishing operations are performed cold to preserve the Q+T microstructure. Final inspection certificate is EN 10204 type 3.1 by default; type 3.2 with notified-body witness is available on request.
Nuts Size Range
Nuts are produced from M6 through M100 thread (and the imperial equivalents 1/4 inch through 4 inch). Length on application; standard catalogue covers 25-1500 mm. Larger and custom dimensions are produced to drawing.
Nuts Applications
Steam turbine HP/IP casing flange nuts, gas turbine bolted-joint nuts, fired-heater bolting nuts. Always supplied with matched-heat washers and bolts when the procurement specification calls for matched-heat bolted joint.
Certification & Traceability
Heat-traceability is maintained from EN 10269 mill bar through machining and Q+T heat-treatment. EN 10204 type 3.1 inspection certificate documents chemistry, mechanicals (room-temperature plus elevated-temperature where the procurement specification calls for it), dimensional report and hardness reading. PMI testing on request. Third-party witness inspection (Lloyds Register, DNV, BV, SGS, TÜV) on call-out.
Frequently Asked Questions
Which Durehete grade should I specify for nuts?
Durehete 1055 / Alloy T41 covers HP turbine and supercritical service to 565°C. Durehete 950 / Alloy T31 covers IP turbine and subcritical to 540°C. Durehete 900 / Alloy T22 covers LP turbine and lower-temperature pressure-vessel service to 500°C.
Are nuts stocked or made-to-order?
Common diameters are stocked in bar form; finished bolting is made-to-order from the bar stock. Lead time on standard sizes is 1-2 weeks; custom sizes 4-8 weeks.
Do you supply ASTM A193 dual certification?
Yes, on Durehete 950 (Alloy T31) which has a documented ASTM A193 Grade B16 cross-reference. Dual certificates are issued from the same heat.
What thread profiles are available?
Metric M-thread (ISO 261 + ISO 965 coarse and fine), Unified inch UN/UNC/UNF (ASME B1.1), and BSW / BSF on request.
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