In refinery, chemical-process and pressure-equipment joints, Type 304 stainless bolting is often specified when the assembly needs corrosion resistance together with the ASTM A193 pressure/high-temperature bolting requirements. ASTM A193 Grade B8 Class 1 is the carbide-solution-treated Type 304 condition. Unlike Class 2, it is not strain hardened, so its mechanical requirements remain the Class 1 baseline across the full size range.
Unifit Fastener manufactures ASTM A193 B8 Class 1 bolts, stud bolts and threaded bolting in India for pressure vessels, valves, flanges, fittings and process piping. For the broader grade overview, see ASTM A193 Grade B8 fasteners. For the wider specification family, see ASTM A193 grades and specifications.
Request a Quote | Send B8 Class 1 SpecificationB8 Class 1 is an austenitic stainless-steel bolting condition based on Type 304 chemistry. The material is carbide solution treated (often described as solution annealed) to place the stainless steel in the required solution-treated condition. Class 1 does not receive the additional strain-hardening step used to raise the strength of B8 Class 2.
That difference matters during purchasing. If the PO only needs the standard solution-treated B8 condition, Class 1 is the correct branch. If the joint design requires the higher strength of strain-hardened B8, the requirement should be written as Class 2 and routed to the dedicated Class 2 page. The fastener marking also changes: Class 1 uses the B8 grade mark, while A193 Class 2 is identified as B8SH.
If your requirement is generic Type 304 / 304L / 304H fasteners rather than ASTM A193 bolting, use the Stainless Steel 304/304L/304H fasteners page instead.
Grade B8 uses Type 304 stainless-steel chemistry. The limits below are the common A193 B8 values used in industry reference tables. The project-specified ASTM A193/A193M revision remains the controlling document for an order.
| Element | B8 limit, % |
|---|---|
| Carbon (C) | 0.08 max |
| Manganese (Mn) | 2.00 max |
| Silicon (Si) | 1.00 max |
| Phosphorus (P) | 0.045 max |
| Sulfur (S) | 0.030 max |
| Chromium (Cr) | 18.0-20.0 |
| Nickel (Ni) | 8.0-11.0 |
The most useful distinction for procurement is that the Class 1 mechanical baseline applies across sizes; it does not step down by diameter in the way the Class 2 strength table does.
| Size | Tensile min | Yield min | Elong. min | RA min | Hardness max | Marking |
|---|---|---|---|---|---|---|
| All sizes | 75 ksi (~515 MPa) | 30 ksi (~205 MPa) | 30% | 50% | 223 HBW / 96 HRB max | B8 |
These properties should be checked together with the material heat treatment, dimensions, thread requirements and purchase-order inspection plan. Do not use Class 1 simply because it is stainless steel; the joint design must accept the Class 1 strength level.
These pages should not compete for the same intent. The simplest way to route them is by material and strength condition:
| Grade / class | Material | Condition | Mechanical logic | Marking | Selection direction |
|---|---|---|---|---|---|
| B8 Class 1 | Type 304 stainless | Carbide solution treated | 75 ksi tensile / 30 ksi yield, all sizes | B8 | Standard solution-treated B8 condition |
| B8 Class 2 | Type 304 stainless | Solution treated + strain hardened | Higher, size-dependent strength | B8SH | Use when the design specifies strain-hardened B8 |
| B8M | Type 316 stainless | Class 1 or Class 2 | Molybdenum-bearing grade; class determines strength | B8M / B8MSH | Consider where 316-type chemistry is required, especially for greater chloride resistance |
Higher-strength sibling: ASTM A193 B8 Class 2 fasteners | Type 316 comparison: ASTM A193 Grade B8M fasteners.
A complete RFQ prevents the wrong class, thread or nut condition from being quoted.
| RFQ field | What to specify |
|---|---|
| Specification | ASTM A193 Grade B8 Class 1; state the ASTM edition if project-controlled |
| Product form | Stud bolt, heavy-hex/hex bolt, threaded stud/rod or drawing-based item |
| Size | Diameter and overall length |
| Thread | 8UN / UNC / UNF / metric as specified; pitch/TPI and class/fit |
| Dimension standard | ASME / ISO / DIN or drawing reference |
| Matching components | ASTM A194 Grade 8 nut requirement and washer requirement |
| Surface / assembly | Plain/passivated/approved finish, lubricant or anti-galling requirement where applicable |
| Quantity / delivery | Project quantity, delivery location and required date |
| Inspection / documents | MTC, PMI, mechanical tests, TPI, marking or project-specific documentation |
Keep the product range centred on pressure-service bolting rather than an unrestricted screw catalogue. Typical B8 Class 1 order forms include:
For generic geometry and dimension information, use the industrial bolts and stud bolts pages.
ASTM A193 defines the bolting material and class; it does not replace the dimensional or thread specification. Headed A193 bolts are commonly supplied in heavy-hex form unless the purchase order states otherwise, and traditional A193 piping work often uses 8UN threads above 1 in. diameter. The PO should still state the required ASME/ISO/DIN or drawing dimensions, thread series, pitch/TPI and class/fit.
For flange assemblies, ASTM A194 Grade 8 heavy-hex nuts are a common matching specification for A193 B8 Class 1 bolting. The nut grade and condition should be written separately rather than described as a “B8 Class 1 nut”.
Related nut specification: ASTM A194 Grade 8 hex nuts.
B8 Class 1 provides Type 304 stainless corrosion resistance, but it is not a universal answer for chloride or seawater exposure. When chloride concentration, temperature or crevice conditions become significant, B8M/Type 316 or a higher-alloy stainless grade may be more appropriate. Material selection should follow the actual corrosion environment and project specification.
Threaded austenitic stainless assemblies also need galling control. Surface finish, thread condition, lubricant, nut material and installation speed can all affect friction and seizure risk. For that reason, a universal B8 Class 1 torque chart should not be published without a defined friction/lubrication basis and target preload. The tightening procedure should be based on the actual assembly condition.
B8 Class 1 is used when the design calls for solution-treated Type 304 stainless bolting under the ASTM A193 pressure/high-temperature specification. Typical project areas include:
Low-temperature note
Do not position this A193 page around cryogenic service. ASTM A320 is the specification family commonly used for low-temperature bolting. If a project requires low-temperature B8, the order should identify the ASTM A320 requirement rather than relying on this A193 Class 1 page.
For project bolting, specify the marking, traceability and inspection scope before production or dispatch. B8 Class 1 is identified by the B8 grade mark together with the manufacturer identification required by the applicable specification.
ASTM A193 Grade B8 Class 1 is the carbide-solution-treated Type 304 stainless-steel condition within ASTM A193. It is used for pressure vessels, valves, flanges, fittings and other special-purpose bolting where the project calls for A193 B8 in the Class 1 condition.
Both use Type 304 stainless chemistry. Class 1 is carbide solution treated and is not strain hardened. Class 2 receives additional strain hardening, which raises strength and introduces size-dependent mechanical requirements. A193 Class 2 is marked B8SH.
Common ASTM A193 reference data lists a minimum tensile strength of 75 ksi, minimum yield strength of 30 ksi, 30% minimum elongation, 50% minimum reduction of area and 223 HBW / 96 HRB maximum hardness for B8 Class 1 across sizes. Verify the project-specified ASTM edition before order release.
No. B8 Class 1 is an ASTM A193 bolting designation with specific solution-treatment, mechanical, marking and inspection requirements. Generic 304 or 304L fasteners may be manufactured to other dimensional or material standards and should not automatically be treated as A193 B8 Class 1.
ASTM A194 Grade 8 heavy-hex nuts are a common matching specification. The final nut condition, dimensions, lubricant or finish and project requirements should be checked as part of the complete bolted-joint specification.
Do not assume so from the stainless-steel designation alone. B8 is Type 304. Where chloride pitting or crevice corrosion is a major concern, the engineering specification may move toward B8M/Type 316 or a higher-alloy grade depending on temperature, concentration and joint conditions.
ASTM A193 is primarily a high-temperature/high-pressure and special-purpose bolting specification. ASTM A320 is the specification family normally associated with low-temperature bolting. If a project requires low-temperature B8, the purchase order should identify the appropriate A320 requirement.
Send the ASTM grade and class, product form, diameter, length, thread, dimensional standard or drawing, matching nut/washer requirement, surface or lubricant requirement, quantity, delivery location and any MTC, PMI, third-party inspection or marking requirement.