ASTM A193
Grade B8 Stud Bolts
Mumbai · India
What Is ASTM A193 Grade B8 Stud Bolts
ASTM A193 is the standard specification for alloy and stainless steel bolting material intended for high-temperature or high-pressure service, most commonly stud bolts used in flanged piping and pressure vessel joints. Grade B8 within that standard specifies austenitic stainless steel — Type 304 (UNS S30400) — chosen for its corrosion resistance and stable mechanical behavior across a wide temperature range, including cryogenic service where many carbon and alloy steel grades become brittle.
What makes Grade B8 easy to misspecify is that the standard defines two distinct strength classes under the same grade name. Class 1 is solution-annealed — soft, ductile, and comparatively low strength, roughly comparable to standard 304 bar stock. Class 2 is strain-hardened through cold working after annealing, which roughly doubles tensile and yield strength while retaining reasonable ductility. A stud bolt drawing that simply says “B8” without a class designation is technically incomplete — the actual strength delivered depends entirely on which class is supplied, and buyers who don’t specify the class often receive Class 1 by default, which may not meet the load the joint was designed around.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our A193 Grade B8 stud bolt range is manufactured in both Class 1 and Class 2 condition, with full mill test documentation confirming the class actually supplied under our ISO 9001:2015 quality system.
Where Class Selection Genuinely Matters
Class Explicitly Confirmed on Every Order
We confirm Class 1 or Class 2 before manufacture, rather than defaulting silently to the weaker annealed condition.
Stable Across Temperature Extremes
Austenitic stainless behavior means reliable performance from cryogenic service through to elevated temperature, without the brittle transition risk of carbon steel.
Corrosion Resistance for Process Piping
Type 304 chemistry resists a broad range of process fluids without the added cost of molybdenum-bearing grades where it isn’t needed.
Full Mill Test Traceability
Every batch traceable by heat number with mechanical property verification confirming the class actually delivered.
Class 1 vs Class 2 vs Grade B8M
Getting Grade B8 right means specifying two things, not one: the class (strength condition) and, if chloride exposure is a concern, whether B8 or the molybdenum-bearing B8M is the correct base grade. The comparison below is the one we walk through with buyers before quoting, so the fastener actually matches the joint’s mechanical and corrosion requirements.
| Property | B8 Class 1 | B8 Class 2 | B8M Class 1 | B8M Class 2 |
|---|---|---|---|---|
| Base Material | Type 304 (S30400) | Type 304 (S30400) | Type 316 (S31600) | Type 316 (S31600) |
| Condition | Solution-annealed | Strain-hardened | Solution-annealed | Strain-hardened |
| Min. Tensile Strength | 75 ksi (515 MPa) | 125 ksi (860 MPa), size dependent | 75 ksi (515 MPa) | 110 ksi (760 MPa), size dependent |
| Min. Yield Strength | 30 ksi (205 MPa) | 105 ksi (725 MPa), size dependent | 30 ksi (205 MPa) | 95 ksi (655 MPa), size dependent |
| Chloride Resistance | Good | Good | Better — molybdenum added | Better — molybdenum added |
| Best Suited For | General corrosion-resistant, low load | Higher-load flanged joints | Mild chloride, low load | Higher-load, chloride-exposed joints |
ASTM A193 B8 Product Range
B8 Class 1 Stud Bolts
Solution-annealed stud bolts for general corrosion-resistant flanged joints at moderate load.
B8 Class 2 Stud Bolts
Strain-hardened stud bolts for higher-load flanged joints requiring greater strength than Class 1.
Grade 8 / 8A Hex Nuts
Matching heavy hex nuts manufactured to pair correctly with B8 Class 1 or Class 2 stud bolts.
B8M Stud Bolts
Molybdenum-bearing Type 316 equivalent for higher chloride resistance in the same class structure.
Grade B8 Technical Overview
Type 304 Alloying Elements
- Chromium 18.0 – 20.0%
- Nickel 8.0 – 11.0%
- Carbon (max) 0.08%
- Manganese (max) 2.0%
- Iron Balance
Property by Class (per ASTM A193)
- Class 1 Tensile 75 ksi min (515 MPa)
- Class 2 Tensile Up to 125 ksi (860 MPa)
- Elongation Min. 12–35%, class dependent
- Hardness Max per diameter, per spec
- Testing MTC / NABL on request
Available Dimensions
- Metric Diameter M6 – M64
- Imperial Diameter 1/4″ – 4″
- Stud Length Custom to drawing
- Thread Type UNC / UNF / 8UN
- Finish As-machined / Passivated
Application Areas
Wherever flanged joints need corrosion resistance across a wide temperature range.
Flanged Process Piping
and high-temperature piping
Pressure Vessels
chemical process equipment
Cryogenic Equipment
mechanical performance
Chemical Processing
resistant flange bolting
Food & Pharmaceutical
process equipment fastening
Power Generation
flanged joint fastening
Marine Piping Systems
joint fastening on vessels
General Process Engineering
flanged bolting
Standard Export Documentation
Prepared as standard practice for every Grade B8 shipment.
Mill Test Certificate (MTC)
Heat number, chemical composition, and mechanical property verification confirming class supplied.
Certificate of Conformance
Confirms the shipment matches the purchase order specification, grade, and class in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
NABL Accredited Test Reports
Independent mechanical and chemical testing available on request for critical applications.
Bill of Lading
Ocean or air freight shipping document confirming carrier, mode, and consignee details.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
Stainless Steel 316 Fasteners
The base material behind Grade B8M, for higher chloride resistance than standard 304.
View SS 316 →High Tensile Bolts Specifications
Carbon and alloy steel property classes for structural and mechanical bolting.
View High Tensile Specs →Super Duplex Fasteners
Higher strength and severe chloride resistance where austenitic stainless isn’t enough.
View Super Duplex →ASTM A193 Grade B8T Fasteners
Titanium-stabilized stainless for high-temperature service beyond standard 304’s carbide-precipitation limit.
View Grade B8T →Need Class 1
or Class 2 Stud Bolts?
Tell us the joint load, temperature, and chloride exposure — and we’ll confirm the right class and grade for your flanged connection. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in