Description
Hardness-controlled pressure bolting for specified service
ASTM A193 Grade B7M Alloy Steel Heavy Hex Bolts
ASTM A193 Grade B7M alloy steel heavy hex bolts combine chromium-molybdenum bolting chemistry with restricted hardness for pressure-equipment connections where the project requires B7M.
What are ASTM A193 B7M heavy hex bolts?
Grade B7M is a modified, hardness-controlled version of ASTM A193 Grade B7. It is commonly selected in project specifications that address sulfide stress cracking risk, but the grade name by itself does not establish compliance with NACE MR0175/ISO 15156 or suitability for a particular sour environment.
For a headed product, the order must identify the heavy hex geometry separately from the B7M material grade. Manufacturing sequence, final heat treatment, hardness verification, thread condition, compatible nut and coating require tighter control than a generic alloy steel bolt order.
Key procurement advantages
ASTM A193 Grade B7M Alloy Steel Heavy Hex Bolts specifications
| Bolting standard | ASTM A193/A193M, ordered edition |
|---|---|
| Grade | B7M |
| Material | Heat-treated chromium-molybdenum alloy steel with restricted hardness |
| Hardness limit | 235 HBW or 99 HRB maximum, subject to the ordered standard requirements |
| Head / dimensions | Heavy hex head to ASME B18.2.1 or project drawing |
| Thread system | UNC, UNF or 8UN to ASME B1.1 as ordered |
| Typical supply range | 1/2 through 4 in. diameter; size, heat treatment and testing subject to review |
| Compatible nut | ASTM A194/A194M Grade 2HM heavy hex nut when specified |
| Finish / coating | Plain or project coating qualified for the material, environment and assembly |
| Sour-service status | NACE MR0175/ISO 15156 compliance only when explicitly ordered and verified for the application |
| Documentation | EN 10204 3.1 MTC, 100% hardness verification when required, traceability and inspection records |
Published ranges are procurement guidance, not a design approval. The purchase order, governing code, standard edition and approved drawing control final dimensions, properties and acceptance criteria.
How to select this grade
| Selection point | ASTM A193 Grade B7M Alloy Steel Heavy Hex Bolts | When to review another grade |
|---|---|---|
| Hardness | Restricted for Grade B7M | Higher permitted hardness for standard Grade B7 |
| Typical selection | Project-specified hardness-controlled pressure bolting | General high-pressure or elevated-temperature B7 service |
| Common nut | ASTM A194 Grade 2HM | ASTM A194 Grade 2H for B7 |
| Sour-service claim | Requires project-specific NACE/ISO verification | B7 is not automatically sour-service compliant |
Matching nuts, washers and coatings
Pair B7M bolts with the ordered hardness-controlled nut, commonly ASTM A194 Grade 2HM. Confirm washer hardness, coating, lubricant and installation procedure. If NACE MR0175/ISO 15156 is required, state the environmental limits, hardness testing, heat-treatment records and any additional certification on the purchase order.
Typical applications
| Industry | Typical duty | Why this grade is specified |
|---|---|---|
| Sour oil and gas | Specified valves, pressure equipment and skids | Restricted hardness where the materials engineer approves B7M |
| Refining | Selected H2S-bearing process services | Project-controlled bolting and documentation |
| Chemical processing | Pressure joints with hardness restrictions | Traceable material and final hardness verification |
| Maintenance | Replacement of existing B7M headed bolting | Grade-for-grade configuration and marking control |
Application examples do not replace engineering review. Confirm load, temperature, pressure, environment, joint design, installation method and governing code before selection.
Inspection, testing and documentation
SASA FLANGE can prepare a project-specific inspection and documentation package. Requirements must be agreed before manufacture so the test frequency, traceability and acceptance criteria are built into the production route.
Testing frequency and individual results documented to the ordered requirements.
Final condition and process route controlled for B7M compliance.
Heat and manufacturing lot maintained through marking and packing.
Additional NACE/ISO declarations and third-party review supplied only when ordered.
RFQ and ordering checklist
- ASTM standard, grade, type and required edition
- Heavy hex dimensional standard or approved drawing
- Diameter, overall length and thread length
- Thread series, pitch and class of fit
- Matching nut and washer standards and grades
- Surface finish, coating, lubrication and color
- Service temperature, environment and design code
- Quantity, marking, packing and delivery destination
- EN 10204 MTC, mechanical, impact, hardness, PMI and NDE requirements
- Third-party inspection or project hold points
Frequently asked questions
What is the difference between ASTM A193 B7 and B7M?
B7M is hardness controlled and has different mechanical and processing requirements. It is often specified where sulfide stress cracking risk is considered.
Does B7M automatically comply with NACE MR0175?
No. Compliance depends on the complete material condition, hardness, environment, product form and project requirements. NACE MR0175/ISO 15156 must be explicitly ordered and verified.
Which nut matches a B7M heavy hex bolt?
ASTM A194 Grade 2HM heavy hex nuts are commonly specified because they provide a compatible hardness-controlled assembly.
Can B7M bolts be coated?
A coating may be supplied only after its chemistry, curing temperature, thickness, lubrication and environmental suitability are reviewed against the project specification.
Which certificates should be requested?
Common requirements include EN 10204 3.1 MTC, heat-treatment records, hardness results, dimensional inspection and any project-specific NACE/ISO documentation.
Request a heavy hex bolt quotation
Send the standard, grade, drawing, size, assembly, service condition, quantity and documentation requirements for technical review.
