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 HP (High-Pressure) Turbine Bolting — Durehete 1055 / Alloy T41 at 540-565°C
HP turbine bolting is the most demanding bolting application in the steam-turbine family. Casing flanges operate at 540-565°C steam temperature with 250+ bar pressure. Durehete 1055 (Alloy T41 / 20CrMoVTiB4-10 / EN 10269) is the standard specification because the Ti+B microalloying covers the 100,000-hour creep-rupture envelope at the upper temperature limit.
HP Service Envelope
HP main steam temperature: 540-565°C. HP main steam pressure: 250-300 bar on subcritical units, 250-265 bar at supercritical inlet. Casing flange bolts see the casing-skin temperature (typically 5-15°C below main steam due to insulation losses) and the full preload required to prevent gasket leak under thermal cycling.
Why Alloy T41
Plain Cr-Mo-V grades like 21CrMoV5-7 lose creep margin above 540°C as M23C6 carbides coarsen at grain boundaries. The Ti+B microalloying in 20CrMoVTiB4-10 (Alloy T41) pins the grain boundaries against carbide coarsening and adds 25-50°C of usable temperature. This is the procurement driver at HP service.
Preload and Stress-Relaxation
HP bolt preload is calculated against the EN 10269 Annex A 0.2 percent proof stress at operating temperature plus the Annex B stress-relaxation curve. Typical initial preload targets 60-65 percent of yield; residual preload at 30,000 hours is 50-55 percent of initial. Re-tightening at major outage typically every 4-6 years.
Bolt Size Range
HP casing flange bolts typically M36 to M100 thread, length 200-1200 mm. TorqBolt produces from EN 10269 / VdTÜV W350 certified bar via custom machining and Q+T heat treatment per the specification.
Frequently Asked Questions
Which Durehete grade is specified for hp (high-pressure) 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 hp (high-pressure) 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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