What Are ASTM A193 Grade B8 Bolts?
ASTM A193 is an American Society for Testing and Materials standard that specifies requirements for alloy and stainless steel bolting materials intended for high-temperature or high-pressure service, and other special-purpose applications such as pressure vessels, valves, flanges and fittings. Grade B8 is one of the most widely specified grades within this standard and covers fasteners manufactured from Type 304 austenitic stainless steel (AISI 304 / UNS S30400).
ASTM A193 Grade B8 bolts are available in two tensile classes Class 1 (carbide solution treated) and Class 2 (carbide solution treated and strain hardened) each with distinct mechanical property requirements to suit different assembly demands. Grade B8 fasteners maintain their mechanical integrity across a broad temperature range from cryogenic conditions as low as −200°C to elevated service temperatures up to 816°C, making them suitable for demanding industrial environments.
Jade Alloys is a Mumbai-based manufacturer and exporter of ASTM A193 Grade B8 bolts in both imperial and metric sizes, supplying to oil and gas, chemical, power and construction industries across India, the Middle East, Europe, South-East Asia and the Americas. All fasteners are supplied with EN 10204 3.1 Mill Test Certificates and are available with dual ASTM/ASME certification on request.
ASTM A193 B8 Quick Reference Specification
| Parameter | Specification / Value |
|---|---|
| Material Grade | Austenitic Stainless Steel — AISI 304 / 304L |
| UNS Designation | S30400 / S30403 |
| Applicable Standard | ASTM A193 / ASME SA193 |
| Tensile Classes | Class 1 (Solution Treated) | Class 2 (Strain Hardened) |
| Sizes Available | M2 to M160 | 1/4″ to 4″ Imperial |
| Temperature Range | -200°C to +816°C |
| Applicable Nut Standard | ASTM A194 Grade 8 |
| Common Applications | Pressure vessels, flanges, heat exchangers, valves |
| Certifications | EN 10204 3.1 MTC | NACE MR0175 | PED 97/23/EC |
ASTM A193 Grade B8 Chemical Composition (AISI 304)
Grade B8 is chemically equivalent to AISI 304 stainless steel, an 18-8 austenitic alloy whose corrosion resistance is derived primarily from its chromium and nickel content. The 18% chromium forms a self-repairing passive oxide layer on the surface, while the 8–11% nickel stabilises the austenitic microstructure and improves toughness. Per ASTM A193, the intentional addition of bismuth (Bi), selenium (Se), tellurium (Te), and lead (Pb) is not permitted.
| Element | Composition (% max unless range stated) | Function |
|---|---|---|
| Carbon (C) | 0.08 max | Hardness balance |
| Manganese (Mn) | 2.00 max | Austenite stabilizer |
| Phosphorus (P) | 0.045 max | Impurity limit |
| Sulfur (S) | 0.030 max | Machinability limit |
| Silicon (Si) | 1.00 max | Deoxidizer |
| Chromium (Cr) | 18.00 – 20.00 | Corrosion resistance |
| Nickel (Ni) | 8.00 – 11.00 | Austenitic structure, toughness |
| Molybdenum (Mo) | Not required (see B8M for Mo-bearing grade) | — |
ASTM A193 Grade B8 Mechanical Properties
The mechanical properties of ASTM A193 B8 bolts depend on the tensile class. Class 1 is carbide solution treated (annealed) and provides moderate, consistent strength across all diameters. Class 2 is additionally strain hardened, which significantly raises tensile and yield strength for smaller diameters — the values step down progressively for larger diameters as the strain hardening effect diminishes with increasing cross-section.
| Property | B8 Class 1 (All Sizes) | B8 Class 2 (≤ 3/4″) | B8 Class 2 (> 3/4″ to 1″) | B8 Class 2 (> 1″ to 1-1/4″) | B8 Class 2 (> 1-1/4″ to 1-1/2″) |
|---|---|---|---|---|---|
| Tensile Strength (min) | 75 ksi / 515 MPa | 125 ksi / 860 MPa | 115 ksi / 795 MPa | 105 ksi / 725 MPa | 100 ksi / 690 MPa |
| Yield Strength 0.2% offset (min) | 30 ksi / 205 MPa | 100 ksi / 690 MPa | 80 ksi / 550 MPa | 65 ksi / 450 MPa | 50 ksi / 345 MPa |
| Elongation in 4D (min %) | 30% | 12% | 15% | 20% | 28% |
| Reduction of Area (min %) | 50% | 35% | 35% | 35% | 50% |
| Hardness (max) | 223 HBW / 96 HRB | 321 HBW / 35 HRC | 321 HBW / 35 HRC | 321 HBW / 35 HRC | 321 HBW / 35 HRC |
ASTM A193 B8 Class 1 vs Class 2 — Key Differences
Selecting the correct tensile class is critical to both joint integrity and code compliance. Class 1 bolts are used in the vast majority of standard pressure-flange assemblies; Class 2 bolts are specified when higher bolt load is needed, most commonly with non-metallic flanges (FRP, CPVC, PVC) where the flange itself is the weakest link and higher fastener clamping force is required. Class 2 bolts also offer greater resistance to galling during assembly because the work-hardened surface is harder than Class 1.
| Feature | Class 1 | Class 2 |
|---|---|---|
| Heat Treatment | Carbide solution treated (annealed) | Carbide solution treated + strain hardened |
| Strength Level | Standard (75 ksi UTS min) | High (125 ksi UTS min for ≤ 3/4″) |
| Hardness (max) | 223 HBW / 96 HRB | 321 HBW / 35 HRC |
| Galling Resistance | Standard | Higher due to work hardening |
| Typical Application | Pressure flanges, general industrial | Non-metallic flanges (FRP, PVC, CPVC) |
| ASTM Marking | B8 | B8 (with class designation) |
| Susceptibility to SCC | Lower | Slightly higher in chloride environments |
Available ASTM A193 B8 Fastener Types
Jade Alloys manufactures the full range of ASTM A193 Grade B8 fastener configurations to match every bolting application. All products are produced to ASME B18.2.1, ASME B16.5, ASME B18.3, DIN 931/933, and ISO 4014/4017 dimensional standards, with thread forms per ASME B1.1 (Unified Inch) and ASME B1.13M (Metric).
| Fastener Type | Standard | Common Sizes | Primary Application |
|---|---|---|---|
| Hex Bolts | ASME B18.2.1 / DIN 931 | 1/4″ – 4″ | M6 – M100 | General flange bolting |
| Heavy Hex Bolts | ASME B18.2.1 / DIN 6914 | 1/2″ – 4″ | M12 – M100 | Structural & pressure joints |
| Stud Bolts (full/double-end) | ASME B16.5 / ASME B18.31.2 | 3/4″ – 4″ | M16 – M100 | Flange assemblies (ASME B16.5) |
| Threaded Rods | DIN 976 / ASME B18.31.3 | 1/4″ – 3″ | M6 – M76 | Through-bolting, anchor systems |
| Socket Head Cap Screws | ASME B18.3 / DIN 912 | 1/4″ – 4″ | M5 – M80 | Limited-access assemblies |
| Heavy Hex Nuts | ASTM A194 Grade 8 | Per bolt size | Mating nut for all B8 bolts |
| Eye Bolts | ASME B18.15 | 1/4″ – 3″ | Lifting & rigging |
| U-Bolts | Custom | Per drawing | Pipe supports, clamps |
| Anchor Bolts | ASME B18.31.5 | 1/2″ – 2″ | Structural anchoring |
ASTM A193 B8 Bolt Dimensions and Size Charts
The following dimensional tables cover the most commonly ordered configurations. Dimensions conform to ASME B18.2.1 (imperial hex bolts and heavy hex bolts) and ISO 4014 (metric hex bolts). For stud bolt lengths as per ASME B16.5 flange ratings, please contact us with your flange class and bore size.
Hex Bolt Dimensions (Partial — ASME B18.2.1, Imperial)
| Nominal Size | Body Dia Max (in) | W/Across Flats (in) | Head Height (in) | Thread Length ≤6″ (in) | Thread Length >6″ (in) |
|---|---|---|---|---|---|
| 1/2 | 0.515 | 3/4 | 11/32 | 1.25 | 1.50 |
| 5/8 | 0.642 | 15/16 | 27/64 | 1.50 | 1.75 |
| 3/4 | 0.768 | 1-1/8 | 1/2 | 1.75 | 2.00 |
| 7/8 | 0.895 | 1-5/16 | 37/64 | 2.00 | 2.25 |
| 1 | 1.022 | 1-1/2 | 43/64 | 2.25 | 2.50 |
| 1-1/4 | 1.277 | 1-7/8 | 27/32 | 2.75 | 3.00 |
| 1-1/2 | 1.531 | 2-3/8 | 1-1/32 | 3.25 | 3.50 |
| 2 | 2.039 | 3-1/8 | 1-23/64 | 4.25 | 4.50 |
Heavy Hex Bolt Size Chart (Metric)
| Diameter (mm) | Width Across Flats (mm) | Head Height (mm) | Nut Size (mm) |
|---|---|---|---|
| M12 | 19 | 8 | 19 |
| M16 | 24 | 10 | 24 |
| M20 | 30 | 13 | 30 |
| M24 | 36 | 15 | 36 |
| M30 | 46 | 19 | 46 |
| M36 | 55 | 23 | 55 |
| M42 | 65 | 26 | 65 |
| M48 | 75 | 30 | 75 |
| M64 | 95 | 40 | 95 |
Torque Chart for ASTM A193 B8 Bolts
The tightening torque values below apply to ASTM A193 B8 Class 2 stud bolts and hex bolts assembled with ASTM A194 Grade 8 heavy hex nuts. Values are based on dry, unlubricated threads. When using a thread lubricant or anti-seize compound (recommended to prevent galling), reduce torque by 25–30%. Always confirm assembly torque to the applicable project specification or ASME PCC-1 guidelines.
| Bolt Diameter | 30% Initial Torque (Nm) | 70% Torque (Nm) | 100% Final Torque (Nm) |
|---|---|---|---|
| 1/2″ | 23 | 53 | 75 |
| 5/8″ | 45 | 104 | 149 |
| 3/4″ | 80 | 186 | 264 |
| 7/8″ | 126 | 294 | 420 |
| 1″ | 190 | 441 | 630 |
| 1-1/4″ | 390 | 911 | 1,302 |
| 1-1/2″ | 702 | 1,638 | 2,339 |
| 2″ | 1,735 | 4,047 | 5,783 |
ASTM A193 B8 vs B8M — What Is the Difference?
The most common sourcing question procurement engineers ask is whether to specify B8 or B8M. Both grades are austenitic stainless steel fasteners under ASTM A193, but they differ in base material and, critically, in corrosion resistance.
Grade B8 is manufactured from Type 304 stainless steel (18% Cr, 8–11% Ni, no molybdenum). Grade B8M is manufactured from Type 316 stainless steel (16–18% Cr, 10–14% Ni, 2–3% Mo). The addition of molybdenum in B8M dramatically improves resistance to chloride-induced pitting corrosion and crevice corrosion. If your application involves seawater, chloride-laden process fluids, or aggressive chemical environments, B8M is the correct specification. For standard industrial applications without significant chloride exposure, B8 is fully adequate and more cost-effective.
| Feature | ASTM A193 B8 | ASTM A193 B8M |
|---|---|---|
| Base Material | Type 304 Austenitic Stainless Steel | Type 316 Austenitic Stainless Steel |
| UNS Number | S30400 | S31600 |
| Chromium Content | 18 – 20% | 16 – 18% |
| Nickel Content | 8 – 11% | 10 – 14% |
| Molybdenum | Not present | 2.00 – 3.00% |
| Chloride Resistance | Good (not ideal for high chloride) | Superior (resists pitting & crevice) |
| Typical Industries | General industrial, power generation | Offshore, marine, pharma, food processing |
| Corrosion Resistance | Good for most environments | Excellent, especially chloride environments |
| Tensile Strength (Class 1 min) | 515 MPa (75 ksi) | 515 MPa (75 ksi) |
| Recommended Nut | ASTM A194 Grade 8 | ASTM A194 Grade 8M |
For offshore or chemical processing applications with chloride exposure, we recommend our ASTM A193 B8M Bolts.
ASTM A193 B8 Equivalent Grades — International Cross Reference
The table below enables procurement engineers working across multiple international standards to confirm material equivalence. All designations refer to the Type 304 austenitic stainless steel alloy that forms the basis of ASTM A193 Grade B8.
| Standard | Country / Region | Designation |
|---|---|---|
| ASTM A193 | USA | Grade B8 (Class 1 / Class 2) |
| ASME SA193 | USA (pressure vessels) | SA193 Grade B8 |
| UNS | North America | S30400 / S30403 (304L) |
| EN / DIN | Europe | 1.4301 / X5CrNi18-10 |
| BS 970 | United Kingdom | 304 S15 / 304 S31 |
| JIS G4303 | Japan | SUS 304 |
| GB/T 20878 | China | 0Cr18Ni9 |
| ISO 3506 | International | A2 (Grade 70 = Class 1 approx.) |
Recommended Mating Hardware for ASTM A193 B8 Bolts
Using the correct mating nuts and washers is essential for both code compliance and preventing galling. Because stainless steel fasteners have a natural tendency to gall (seize) during assembly when two 304 surfaces are tightened together under load, the use of a nickel-based anti-seize lubricant is strongly recommended on all threads before assembly.
| Component | Recommended Specification | Material / Grade |
|---|---|---|
| Heavy Hex Nut | ASTM A194 Grade 8 | 304 Stainless Steel |
| Flat Washer | ASTM A240 Type 304 | 304 Stainless Steel |
| Thread Lubricant | ASME PCC-1 / Molykote 1000 or Never-Seez | Nickel-based anti-seize |
| Spring Washer (optional) | DIN 127 — Grade A2 | 304 Stainless Steel |
Applications and Industries for ASTM A193 B8 Bolts
ASTM A193 Grade B8 bolts are specified wherever a combination of corrosion resistance, elevated temperature capability, and code compliance is required. The following industries and applications represent the primary markets we supply:
| Industry / Application | Why B8 Is Specified | Typical Fastener Type |
|---|---|---|
| Oil & Gas — Upstream/Midstream | Corrosion resistance to H₂S, CO₂, brine | Stud bolts, heavy hex bolts |
| Chemical Processing Plants | Resistance to acids, alkalis; high-temp service | Stud bolts, socket head cap screws |
| Power Generation (Conventional) | High-temp pressure vessel flanges | Stud bolts, heavy hex bolts |
| Pulp & Paper Mills | Resistance to bleach and acidic environments | Hex bolts, threaded rods |
| Pharmaceutical Manufacturing | Cleanability, corrosion resistance | Socket head cap screws, hex bolts |
| Wastewater Treatment Plants | Corrosion resistance in wet environments | Hex bolts, anchor bolts |
| Shipbuilding (non-chloride zones) | General corrosion resistance | Hex bolts, stud bolts |
| Wind Turbine Nacelles | Vibration resistance, weather exposure | High-strength hex bolts |
| Heat Exchanger Flanges | ASME Section VIII compliance | Stud bolts (ASME B16.5) |
Certifications and Quality Assurance
Every ASTM A193 Grade B8 fastener supplied by Jade Alloys is manufactured from certified raw materials and subjected to dimensional inspection, hardness testing, and positive material identification (PMI) before dispatch. We supply complete documentation packages to support procurement, QA audits, and regulatory compliance.
| Certification / Compliance | Coverage | Purpose |
|---|---|---|
| EN 10204 3.1 Mill Test Certificate | All ASTM A193 B8 fasteners | Material traceability for buyer |
| NACE MR0175 / ISO 15156 | H₂S-containing environments | Sour service compliance |
| NACE MR0103 | Refinery environments | Wet H₂S compliance |
| PED 97/23/EC | Pressure equipment for EU market | European compliance |
| Merkblatt AD 2000 W2 | German pressure vessels | Germany/EU market |
| Dual Certification ASTM & ASME | B8 & SA193 B8 | Dual-stamp for US pressure codes |
| Third-Party Inspection | SGS / Bureau Veritas / TUV on request | Independent material verification |
| Mercury & Radioactive Contamination Free | All materials | Nuclear adjacent applications |
Why Source Your ASTM A193 B8 Bolts from Jade Alloys?"
Jade Alloys is an ISO-certified manufacturer and exporter of high-performance fasteners based in Mumbai, India — the country’s centre for specialty metals and fastener manufacturing. We supply ASTM A193 Grade B8 bolts to engineering contractors, EPC companies, distributors, and end-users across the globe, with a track record of on-time delivery and full documentation compliance.
- ISO-certified manufacturing with full material traceability from melt origin to finished product
- In-house hardness testing, dimensional inspection, and PMI (Positive Material Identification)
- Stocked inventory for fast dispatch; custom lengths and finishes available on order
- Export-ready documentation: commercial invoice, packing list, COO, MTCs, inspection reports
- Regularly supplying to projects in UAE, Saudi Arabia, Qatar, Oman, UK, Germany, Singapore, Malaysia, USA
Frequently Asked Questions — ASTM A193 B8 Bolts
ASTM A193 Grade B8 Bolts Exporters
Jade Alloys exports ASTM A193 Grade B8 bolts from Mumbai to petrochemical plants, oil & gas facilities, power stations, offshore platforms, EPC contractors, and industrial processing units worldwide.
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