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 Couplings — Shaft, Flange & Expansion-Joint Couplings
Durehete-grade couplings are forged or machined from EN 10269 Cr-Mo-V and Cr-Mo-V-Ti-B bar stock for high-temperature service in steam-turbine shaft drives, flange-to-flange interfaces and expansion-joint terminations. The grade selection follows the same temperature-ladder logic as the Durehete bolting family.
Shaft Couplings
Steam turbine shaft couplings transmit torque between adjacent rotor stages. Durehete 1055 / Alloy T41 covers HP-section shaft couplings at 540-565°C. The Ti+B microalloying handles the combined torque-plus-thermal-cycle loading across the rotor service life.
Flange Couplings
Flange couplings between casing modules use Durehete 950 / Alloy T31 in IP service and Durehete 1055 in HP service. The bolt + nut + washer + flange assembly is a single procurement package; mill traceability covers each component back to the heat number on the EN 10204 type 3.1 / 3.2 certificate.
Expansion-Joint Couplings
Expansion-joint couplings absorb thermal growth between modules. The cyclic loading drives fatigue + creep interaction; Durehete 1055 covers the HP-side expansion joints; Durehete 900 / Alloy T22 covers the LP-side at lower temperature.
Forging Route
Couplings are open-die or closed-die forged from EN 10269 bar stock to near-net shape, then heat-treated (austenitise 970-1010°C, oil/water quench, temper 660-730°C minimum 2 hours air cool) and machined to drawing tolerance. EN 10204 type 3.1 inspection certificate documents chemistry, mechanicals and dimensions.
Frequently Asked Questions
Which Durehete grade is specified for HP turbine shaft couplings?
Durehete 1055 / Alloy T41 / 20CrMoVTiB4-10 covers HP shaft service at 540-565°C. The Ti+B microalloying handles the long-duration creep envelope at upper service temperature.
Are Durehete couplings forged or machined from bar?
Both. Larger couplings are forged to near-net shape from EN 10269 bar then machined; smaller couplings are machined directly from bar. The heat-treatment cycle is identical.
What inspection certificate accompanies Durehete couplings?
EN 10204 type 3.1 by default. Type 3.2 with notified-body witness is available when the procurement specification calls for it. Both document the heat number and mill traceability.
Is dimensional tolerance held to a particular standard?
Tolerances follow the procurement drawing. ISO 2768 medium-grade tolerance applies by default for non-critical dimensions; tighter tolerances per the drawing for fit surfaces.
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