Description
ASTM A193 B8 / B8M Stud Bolts & ASTM A194 8 / 8M Nuts
A193 B8 / B8M Stud Bolt
A Stud Bolt is a cut-to-length, fully or partially threaded rod, widely used for bolting together flanges, pipe fittings, valves, and other critical joints. Stud bolts are externally threaded fasteners without a head and are generally used with two heavy hex nuts—one on each side.
Unlike conventional bolts, stud bolts do not twist during tightening. Instead, they remain stationary while nuts are tightened, which provides:
- Accurate torque values,
- Even clamping forces,
- Improved reliability in sealing critical flange connections.
B8 and B8M stud bolts are manufactured in accordance with ASTM A193, which is the standard specification for alloy steel and stainless-steel bolts intended for high-temperature or high-pressure service.
Material & Grades
- ASTM A193 Grade B8: Manufactured from AISI 304 stainless steel (18Cr-8Ni), providing good corrosion resistance and high-temperature strength.
- ASTM A193 Grade B8M: Manufactured from AISI 316 stainless steel (18Cr-12Ni-2.5Mo), providing excellent resistance to corrosion, especially in chloride and marine environments.
Both grades are available in:
- Class 1 (Solution Annealed) → standard strength.
- Class 2 (Strain Hardened) → higher strength.
General Applications
- Pipeline flanges in oil, gas, and petrochemical industries.
- Refineries, chemical plants, and power generation.
- Marine and offshore environments (B8M preferred due to superior chloride resistance).
- High-pressure and high-temperature service.
- Equipment requiring corrosion resistance + mechanical strength.
Threading & Dimensions
- Available in UNC (Unified National Coarse) thread series, typically used in flange applications.
- Standard thread classes:
- 2A → external (stud bolts)
- 2B → internal (nuts)
- Stud bolts are cut according to flange size, bolt circle diameter, and flange pressure class.
ASTM A194 Grade 8 / 8M Nuts
To match the corrosion and mechanical properties of B8/B8M stud bolts, ASTM A194 Grade 8 & 8M heavy hex nuts are used:
- Grade 8 Nuts → AISI 304 stainless steel (to pair with B8 studs).
- Grade 8M Nuts → AISI 316 stainless steel (to pair with B8M studs).
- Threads: Class 2B internal threads.
- Nuts are designed to ensure uniform load distribution and reliable joint integrity.
Mechanical Properties (Typical)
| Grade | Class | Tensile Strength (min) | Yield Strength (min) | Hardness | Application |
| B8 (304) | Class 1 | 515 MPa | 205 MPa | 159–223 HB | General high-temp service |
| B8 (304) | Class 2 | 860 MPa | 620 MPa | 321 HB max | Higher strength requirement |
| B8M (316) | Class 1 | 515 MPa | 205 MPa | 159–223 HB | Marine/chemical resistance |
| B8M (316) | Class 2 | 860 MPa | 620 MPa | 321 HB max | Offshore/high chloride areas |
Summary
- B8 (304 SS) → General purpose, good corrosion resistance, widely used.
- B8M (316 SS) → Superior corrosion resistance, especially against chlorides, acids, and marine conditions.
- Nuts (A194 8 / 8M) are matched to the respective stud bolts for full compatibility.
- These fasteners are critical in industries requiring strength + corrosion resistance + reliability in bolted joints.
A193 B8 / B8M
