Ferralium 255 hex bolts are machined from ASTM A479 (UNS S32550) bar with ASME B18.2.1 dimensional standard (UNC inch and metric M). Manufactured at TorqBolt's Mumbai & Rajkot, India facilities. Per-heat Mill Test Certificate (EN 10204 type 3.2) certifies hardness ≤ 32 HRC for NACE MR0175 sour-service compliance. NORSOK M-650 QTR available on request for North Sea / Norwegian offshore service.
| Bolt type | Inch series | Metric series |
|---|---|---|
| Hex bolts | ASME B18.2.1 (UNC / UNF) | ASME B18.2.3.1M / DIN 933 (M) |
| Heavy hex bolts | ASME B18.2.1 | ASME B18.2.3.6M |
| Hex cap screws | ASME B18.2.1 | DIN 933 (full thread) / DIN 931 (partial thread) |
Bar stock per ASTM A479 (UNS S32550): Cr 24–27%, Ni 4.5–6.5%, Mo 2.9–3.9%, Cu 1.5–2.5%, N 0.10–0.25%. Solution-annealed at 1100 °C + water quench. Bolt mechanical properties: yield ≥ 550 MPa, tensile ≥ 760 MPa, elongation ≥ 15%, hardness 25–32 HRC (controlled to NACE MR0175 limit). PREN ≥ 40, CPT ≥ 35 °C per ASTM G48 method A.
| Series | Diameter range | Length range |
|---|---|---|
| UNC inch | 1/4" through 4" | up to 36" |
| Metric (M) | M6 through M100 | up to 1000 mm |
Hex bolts are typically supplied with paired fasteners for ASME B16.5 flange connections: Ferralium 255 hex nuts (ASTM A479 material per ASME B18.2.2), flat washers (ASTM A479 material per ASME B18.22.1), and where stud bolts are preferred, Ferralium 255 stud bolts (ASTM A193 S6 / ASME B18.31.2). All paired fasteners come from the same heat where possible to ensure matched corrosion behaviour in service.
