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 Gas Turbine Bolts (EN 10269 / 1.7709)
21CrMoV5-7 gas turbine bolts are specified into compressor casing flanges, combustor liner flanges and turbine outer-case bolting on industrial gas turbines where metal temperatures sit in the 200 to 550 deg C window. The Cr-Mo-V Q+T chemistry resists thermal-cycle relaxation through the start-stop cycles characteristic of peaking and load-following gas turbines.
Service Envelope
| Gas turbine stage | Typical metal temp | 21CrMoV5-7 use |
|---|---|---|
| Inlet casing | 20 to 50 deg C | n/a (carbon steel acceptable) |
| Compressor casing (front) | 50 to 200 deg C | Optional; 42CrMo4 acceptable |
| Compressor casing (rear) | 200 to 500 deg C | Primary choice |
| Combustor outer casing | 400 to 550 deg C | Primary choice; design margin tight |
| Turbine outer case (LP) | 400 to 550 deg C | Primary choice |
| Turbine outer case (HP) | 550 to 700 deg C | Outside envelope; Durehete 1055 or nickel-base |
Bolting Form Factors Used
- Stud Bolts: double-end equal-thread studs for casing half-joint bolting
- Tap Studs: blind-tap-end studs into combustor outer casing
- Body-Bound Studs: precision-fit ground-shank studs for cyclic-load joints
- Heavy Hex Bolts: ASME B18.2.1 head-form bolts for industrial gas-turbine flanges
- Matched-grade nuts and washers
Mechanical Floors for Gas Turbine Bolts Service
| Property | Value | Condition |
|---|---|---|
| Tensile (Rm) | 700 to 850 MPa | RT, Q+T |
| 0.2 percent proof stress (Rp0.2) | ≥550 MPa | RT, Q+T |
| Elongation A5 | ≥16 percent | RT, longitudinal |
| Charpy V impact (KV) | ≥63 J | 20 deg C |
| 0.2 percent proof at 500 deg C | ≥450 MPa | elevated-temp |
| Hardness | 210 to 250 HBW | Q+T |
Standards Anchor
21CrMoV5-7 gas turbine bolts to EN 10269. Cross-procurement on US-design gas turbines (GE, Siemens-Westinghouse) uses ASTM A193 Grade B16 with dual-certification. Combustor and turbine outer-case bolting on the HP end (above 550 deg C) steps up to Durehete 1055.
When to Step Up the Grade
For service above 550 deg C metal temperature, the design steps up to Durehete 1055 (Alloy T41 / Werkstoff 1.7729 / 20CrMoVTiB4-10) with Ti+B microalloying for extended creep envelope. For heavier sections of the same temperature window, sister grade 21CrMoV5-11 (1.8070) provides extended hardenability.
Frequently Asked Questions
Q. What gas turbine OEMs specify 21CrMoV5-7?
Siemens Energy gas turbines (SGT-300 / SGT-500 / SGT-700 / SGT-8000H families), GE / Baker Hughes industrial gas turbines (Frame 6 / Frame 7 / Frame 9), Mitsubishi Power H-class, BHEL industrial gas turbines, Alstom (now GE) GT26 family. The grade is the European-derived workhorse for compressor and combustor casing bolting.
Q. How is the metal-temperature envelope set for gas turbine bolting?
By the design steady-state metal temperature at the bolt location plus a thermal-cycling allowance for start-stop and load-following service. Peaking gas turbines cycle daily; combined-cycle base-loaded units cycle less. The cycling allowance reduces the allowable design stress by 5 to 15 percent.
Q. Are body-bound studs used in gas turbine casings?
Yes. On compressor casing half-joints where cyclic thermal expansion would rock a clearance-fit bolt, body-bound studs with H7/n6 fit transfer the shear load through the bolt body.
Q. What is the difference between gas turbine and steam turbine bolting selection?
Steam turbine bolting sees more steady-state high-temperature service; gas turbine bolting sees more thermal cycling. 21CrMoV5-7 handles both within the 550 deg C envelope, with cycling design margin set in the gas turbine application.
Related Applications
More 21CrMoV5-7 service applications: Steam 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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