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 in Steam Turbine Bolting — HP, IP and LP Casing Flange Bolting
Steam turbine casing flange bolting is the primary application for the Durehete family. HP turbine casings operate at 540-565°C steam temperature; IP turbines run at 480-540°C; LP turbines drop below 400°C. Grade selection follows the temperature ladder.
HP Casing Bolting
HP turbine casing flange bolts are specified in Durehete 1055 / Alloy T41 / 20CrMoVTiB4-10. The Ti+B microalloying delivers the 100,000-hour creep-rupture envelope at 540-565°C steam temperature. Bolt diameters typically 36 to 100 mm; preload calculations follow EN 10269 Annex A and Annex B.
IP Casing Bolting
IP turbine casing bolts run in Durehete 950 / Alloy T31 / 40CrMoV4-6 at 480-540°C. Identical heat-treatment cycle to 1055 but the simpler Cr-Mo-V chemistry (no Ti+B) reduces mill cost while still covering the IP service envelope.
Throttle and Stop-Valve Bolting
Throttle valve and stop-valve bolting on the HP steam side runs in Durehete 1055. The cyclic thermal stress combined with high preload requirement makes the 1055 stress-relaxation envelope the procurement driver.
Inspection and Re-Tightening Cycle
Stress-relaxation curves in EN 10269 Annex B set the re-tightening interval. For HP bolts at 540°C, residual preload drops to ~70 percent at 1,000 hours and ~50 percent at 30,000 hours. Re-tightening typically scheduled at major outages every 4-6 years.
Frequently Asked Questions
Which Durehete grade is specified for steam turbine bolting?
The grade depends on service temperature. Durehete 1055 (T41 / 1.7729) covers up to 565 degrees Celsius; Durehete 950 (T31 / 1.7711) covers up to 540 degrees Celsius; Durehete 900 (T22 / 42CrMoV5-6) covers up to 500 degrees Celsius.
What standard governs steam turbine bolting?
EN 10269 is the controlling European bolting-steel standard. ASTM A193 Grade B16 is the closest US equivalent for the lower-temperature grades (Durehete 950 and 900).
Are dual certificates available?
Yes. TorqBolt supplies the Durehete grades with EN 10269 type 3.1 / 3.2 inspection certificates plus ASTM A193 dual certification when the procurement specification requires it.
What is the typical lead time?
Lead time depends on size and quantity. Stock sizes ship within a week; custom-machined fasteners run 4-8 weeks from heat traceability through to delivery.
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