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 Boiler Bolts (EN 10269 / 1.7709)
21CrMoV5-7 boiler bolts are specified into drum-head bolting, steam-pipe flange bolting and access-door bolting on conventional fossil-fired, biomass-fired, and waste-heat-recovery boilers. The Cr-Mo-V Q+T chemistry holds preload through the long-duration high-temperature service that defines boiler bolting (typically 95+ percent annual run hours).
Service Envelope
| Boiler position | Typical metal temp | 21CrMoV5-7 use |
|---|---|---|
| Drum-head flange | 320 to 380 deg C | Primary choice |
| Steam-pipe flange (main) | 480 to 540 deg C | Primary choice |
| Reheater inlet header flange | 500 to 540 deg C | Primary choice |
| Reheater outlet header flange | 540 to 568 deg C | 21CrMoV5-7 up to 550; Durehete 1055 above |
| Access door bolting | 200 to 320 deg C | Primary choice; 42CrMo4 acceptable |
Bolting Form Factors Used
- Stud Bolts: drum-head and steam-pipe flange bolting
- Heavy Hex Bolts: access-door bolting and inspection-port bolting
- Tap Studs: blind-tap-end bolting on drum-head designs
- Heavy hex nuts to ASME B18.2.2 or DIN 6915 in matched grade
Mechanical Floors for Boiler 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 boiler bolting to EN 10269. Pressure-vessel parallel approval to VdTUV Wb 350 for steam-drum and pressure-part bolting. Cross-procurement on US-design boilers uses ASTM A193 Grade B16 with dual-certification.
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. Which boiler positions use 21CrMoV5-7 versus Durehete 1055?
21CrMoV5-7 covers drum-head, main steam-pipe and reheater inlet header flanges (up to 540 deg C). Reheater outlet header flanges and final superheater flanges (540 to 568 deg C) step up to Durehete 1055 for the Ti+B microalloyed creep envelope.
Q. Are boiler bolts inspected differently from turbine bolts?
Same inspection categories (EN 10204 type 3.1 default, type 3.2 with witness on call-out). Boiler bolts often see additional pressure-vessel notified-body witness (TUV Rheinland, TUV SUD) under the German PED for steam-drum and main-pressure-part bolting.
Q. What is the typical replacement cadence for boiler bolts?
Inspection-driven at each major outage (typically 4 to 6 year cadence). Bolt hardness, dimensional check (thread engagement, stretch measurement), and visual inspection determine replacement. Bolts that drop below 200 HBW or show >0.5 percent permanent stretch are replaced.
Q. Do you supply matched-grade nuts and washers for boiler bolting?
Yes. Matched-grade heavy hex nuts to ASME B18.2.2 or DIN 6915 and matched-grade hardened washers to DIN 6916 ship from the same heat lot on call-out and standard practice on boiler procurement.
Related Applications
More 21CrMoV5-7 service applications: Steam Turbine Bolts · Gas Turbine Bolts · Power Plant Bolting · Pressure Vessel Bolts · Heat Exchanger Bolts · Fired Heater Bolts · Petrochem Reactor Bolts. Back to the 21CrMoV5-7 Alloy Hub.
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