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
21CrMoV5-7 Steam Turbine Bolts (EN 10269 / 1.7709)
21CrMoV5-7 steam turbine bolts hold the casing halves, valve bodies and steam-line flanges of LP, IP and lower-HP turbine stages. To EN 10269, the grade carries continuous service to 550 deg C metal temperature with Cr-Mo-V Q+T creep performance. Above 550 deg C the design steps up to Durehete 1055 (Alloy T41 / 1.7729) for the Ti+B microalloyed creep envelope. TorqBolt supplies the full bolting set: studs, nuts, washers, threaded rod and tap studs from the same heat lot.
Steam Turbine Service Envelope
| Stage | Typical metal temp | 21CrMoV5-7 use | If above envelope |
|---|---|---|---|
| LP (low-pressure) | 200 to 380 deg C | Primary choice; cost-effective vs Durehete | n/a |
| IP (intermediate-pressure) | 400 to 530 deg C | Primary choice; full creep envelope | n/a |
| HP (high-pressure, lower stages) | 500 to 550 deg C | Primary choice; design margin tight | Step to Durehete 1055 above 550 |
| HP (high-pressure, upper stages) | 550 to 568 deg C | Outside envelope | Durehete 1055 (Alloy T41 / 1.7729) |
| Supercritical HP main | 568 to 600 deg C | Outside envelope | Durehete 1055 with USC creep margin |
Bolting Form Factors Used in Steam Turbine Casings
- Stud Bolts: double-end equal-thread studs for casing half-joint and steam-line flange bolting
- Tap Studs: blind-end tap studs into the casing on one end, nut-end the other, for half-joint and valve-body bolting
- Body-Bound Studs: precision-fit ground-shank studs to H7/n6 for cyclic-load casing joints where shear transfers through the body
- Heavy Hex Bolts: ASME B18.2.1 head-form bolts for flange-mating service
- Nuts and washers: matched-grade companion hardware from the same heat lot
Mechanical Floors for Steam-Turbine Service
| Property | RT | 500 deg C | 550 deg C |
|---|---|---|---|
| 0.2 percent proof stress (Rp0.2) | >=550 MPa | >=450 MPa | >=420 MPa |
| Tensile (Rm) | 700 to 850 MPa | >=600 MPa | ~600 MPa |
| Elongation A5 | >=16 percent | maintained | maintained |
| Stress-rupture (100,000 h) | n/a | >=260 MPa | >=180 MPa |
Standards Anchor
21CrMoV5-7 steam-turbine bolting is specified to EN 10269 for chemistry, mechanicals and inspection categories. Pressure-vessel parallel approval to VdTUV Wb 350 for combined turbine-pressure-vessel assemblies. Cross-procurement on US-design turbines uses ASTM A193 Grade B16 with dual-certification on call-out.
When to Step Up the Grade
For HP main steam casings above 550 deg C, supercritical main bolting, and ultra-supercritical projects, the design steps up to Durehete 1055 (Alloy T41 / Werkstoff 1.7729 / 20CrMoVTiB4-10) with Ti+B microalloying for the extended creep envelope. For heavier sections of the same temperature window, the sister grade 21CrMoV5-11 (1.8070) provides extended hardenability without changing the alloy class.
Frequently Asked Questions
Q. What is the metal-temperature envelope for 21CrMoV5-7 in steam turbine bolting?
Up to 550 deg C continuous metal temperature to EN 10269. Covers LP, IP and lower-HP casings. Above 550 deg C the design steps up to Durehete 1055.
Q. Which stud form is used for steam turbine half-joint bolting?
Tap studs and body-bound studs. Tap studs anchor into a blind tapped hole; body-bound studs have a ground precision shank to H7/n6 for cyclic-load joints.
Q. Do you supply matched-grade nuts and washers from the same heat lot?
Yes. Companion nuts and washers in 21CrMoV5-7 from the same heat lot as the stud are supplied on call-out and are standard practice on turbine procurement.
Q. What PWHT cycle do you use for welded steam-turbine attachments?
PWHT at 690 to 720 deg C, 1 hour per 25 mm minimum 2 hours, slow furnace cool to 300 deg C, then air cool. Hardness traverse verifies the PWHT achieved the intended tempering.
Related Applications
More 21CrMoV5-7 service applications: Gas Turbine Bolts · Power Plant Bolting · Pressure Vessel Bolts · Boiler Bolts · Heat Exchanger Bolts · Fired Heater Bolts · Petrochem Reactor Bolts. Back to the 21CrMoV5-7 Alloy Hub.
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