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 Body-Bound Studs (EN 10269 / 1.7709) Cr-Mo-V Q+T Bolting
21CrMoV5-7 body-bound studs (also called reamer bolts or precision-fit studs) are double-end studs with a ground precision shank to H7/n6 fit class so the bolt-up shear load is transferred through the body of the stud, not through the threads. The dominant fastener for cyclic-load steam-turbine half-joints where vibration and thermal cycling would loosen a clearance-fit bolt.
Body-Bound Studs Designs and Variants
The shank is ground to a tight clearance in the reamed hole. Standard fit is H7/n6 (median interference 12 micrometres on a 50 mm shank). Tighter H7/p6 or H7/r6 on call-out for high-cycle service. The thread ends are standard metric or Unified to the same standards as tap studs.
Size Range
| Fit class | Shank tolerance (50 mm OD) | Use case |
|---|---|---|
| H7/n6 (standard) | 0 to +33 μm interference | Steam turbine half-joints, gas turbine casings |
| H7/p6 (tighter) | +17 to +51 μm interference | High-cycle HP turbine joints |
| H7/r6 (tightest) | +34 to +67 μm interference | Vibration-critical service |
Mechanical Properties (Q+T, EN 10269)
| 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
Manufactured to EN 10269 chemistry and mechanicals. Shank ground to ISO 286-2 H7/n6 (or tighter on call-out). Surface roughness Ra typically 0.4 to 0.8 micrometre on the ground shank. Dimensional report on every stud includes the shank diameter measured at three positions (top, middle, bottom) verifying the H7/n6 tolerance.
Companion Hardware
Matched-grade Cr-Mo-V companions ship from the same heat lot on call-out: 21CrMoV5-7 nuts, washers, threaded rod, stud bolts and round bar.
Applications
Body-bound studs are specified almost exclusively in steam turbine HP and IP casing half-joints (Siemens, GE, BHEL, Mitsubishi Power procurement) and in gas turbine combustor and compressor casings where bolt-up cyclic shear loading requires through-body load transfer instead of thread-only transfer.
Inspection Documentation
Default delivery is EN 10204 type 3.1 mill test certificate with heat number, melt-shop pour record, chemistry to EN 10269 21CrMoV5-7, room-temperature tensile and 0.2 percent proof stress, elevated-temperature 0.2 percent proof at the design temperature, Charpy V impact at 20 deg C, hardness, full Q+T cycle chart and dimensional report tied to the heat lot. Type 3.2 with Lloyd's Register, DNV, BV, SGS or TUV witness inspection on call-out and standard practice on turbine and pressure-vessel procurement.
Frequently Asked Questions
Q. What is the fit-class tolerance on a body-bound stud?
Standard fit class is H7/n6 to ISO 286-2. On a 50 mm shank: hole tolerance H7 is 0 to +25 micrometres; shank tolerance n6 is +17 to +33 micrometres. Net interference is 0 (worst case) to +33 micrometres (best case), median 12 micrometres for full-life shear transfer.
Q. Why grind the shank instead of using a hex bolt with a clearance fit?
Cyclic thermal expansion of a steam-turbine casing half-joint can rock the bolt in a clearance-fit hole, fatiguing the bolt body and the casing bore. A body-bound stud transfers the shear load through the bolt body via metal-to-metal interference contact, eliminating the rocking.
Q. What is the maximum body-bound stud diameter?
M120 in metric and 4 inch in Unified. Surface finish Ra 0.4 to 0.8 micrometre on the ground shank, dimensional report on every stud verifying the H7/n6 tolerance.
Q. Do you supply body-bound studs with EN 10204 type 3.2 certification?
Yes. Type 3.2 with Lloyd's, DNV, BV, SGS or TUV witness is the standard practice on every Siemens, GE, BHEL, Mitsubishi Power turbine half-joint procurement.
Related 21CrMoV5-7 Form Factors
Browse the full 21CrMoV5-7 form-factor range: Round Bar · Stud Bolts · Hex Bolts · Heavy Hex Bolts · Tap Studs · Anchor Bolts · U-Bolts · Threaded Rod · Nuts · Washers · Forgings. Back to the 21CrMoV5-7 Alloy Hub.
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