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 Hex Bolts — Alloy T41 / T31 / T22 (EN 10269 Cr-Mo-V Bolting Steel)
Durehete hex bolts are the standard hex-head pattern per ASME B18.2.1 / ISO 4014. The standard across-flats dimension delivers the lowest cost per bolt where flange-face bearing pressure isn't the design constraint.
Durehete Grade Selection for Hex Bolts
| 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
Hex Bolts 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.
Hex Bolts Size Range
Hex Bolts 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.
Hex Bolts Applications
Steam turbine LP casing flange bolting, gas turbine compressor casing bolts, balance-of-plant flange bolting in supercritical power plants.
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 hex bolts?
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 hex bolts 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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