Description
Hardness-controlled alloy-steel flange bolting
ASTM A193 B7M Stud Bolts with A194 2HM Nuts
ASTM A193 Grade B7M fully threaded stud bolts with matching ASTM A194 Grade 2HM heavy hex nuts, supplied with the required heat treatment, hardness verification and traceability.
Quick answer
ASTM A193 B7M stud bolts are chromium-molybdenum alloy-steel bolting with grade-specific heat-treatment and hardness-control requirements. They are often selected for project-defined sour or controlled-hardness service, but compliance with NACE MR0175/ISO 15156 is a separate engineering and purchasing requirement.
Product at a glance
What are ASTM A193 B7M stud bolts?
B7M is a distinct ASTM A193 bolting grade, not a surface-finish variation of B7. Its manufacture requires control of heat treatment, mechanical properties and hardness in accordance with the ordered ASTM edition. When supplied as a set, the stud bolts are commonly paired with ASTM A194 Grade 2HM heavy hex nuts.
B7M is frequently referenced in sour-service material specifications because hardness can influence susceptibility to environmental cracking. However, the grade designation alone does not prove suitability for a particular H2S environment. The equipment owner or designer must specify the applicable NACE or ISO requirements, environmental limits and documentation.
ASTM A193 B7M stud bolt specifications
| Material | Chromium-molybdenum alloy steel |
|---|---|
| Grade control | Heat treated and hardness controlled to ASTM A193/A193M B7M |
| Configuration | Fully threaded stud bolt; custom double-end studs by drawing |
| Threads | UNC, 8UN or project-specified series and class to ASME B1.1 |
| Dimensions | ASME B18.31.2, flange bolting schedule or approved drawing |
| Matching nuts | ASTM A194/A194M Grade 2HM when specified |
| Finish options | Plain or approved project coating with hardness and process controls maintained |
| Special service | NACE MR0175/ISO 15156 only when explicitly specified and technically reviewed |
Final dimensions, tolerances, heat treatment, mechanical properties, impact or hardness requirements, coating and acceptance criteria follow the purchase order and the contractually specified standard edition.
Why specify this grade?
Select B7M when the project bolting specification requires the B7M grade and its controlled-hardness production route. It is commonly paired with 2HM nuts for flange joints where materials, hardness and traceability are tightly controlled.
Critical engineering note
B7M is not created by coating B7. Cutting, threading, heat treatment, hardness testing, plating and rework must follow the ordered specification. A statement of NACE compliance also requires the exact standard edition, service environment and purchaser requirements.
Stud, nut and finish options
Typical applications
Quality, inspection and documentation
B7M orders require disciplined material identification and hardness records. SASA FLANGE can coordinate the certificate package, finished-product inspection and optional third-party witness points stated in the inquiry.
- EN 10204 3.1 material test certificate when ordered
- Heat-number and manufacturing-batch traceability
- Chemical composition and mechanical-property results
- Hardness testing at the frequency required by the ordered grade
- Charpy impact testing for low-temperature grades as specified
- Dimensional inspection and calibrated thread gauging
- Coating thickness or surface-condition inspection when applicable
- Third-party inspection, marking and export packing by agreement
Information required for quotation
- ASTM standard, grade and contractually required edition
- Stud diameter, overall length, thread series and thread class
- Quantity and whether two nuts per stud are required
- Matching nut specification, grade, style and finish
- Plain, coated or plated finish and the approved coating system
- Design temperature, impact-test temperature and sour-service requirements when relevant
- MTC, PMI, hardness, impact, coating and third-party inspection requirements
- Delivery destination, packing method and required schedule
Frequently asked questions
What is the difference between B7 and B7M stud bolts?
B7M is a separate ASTM A193 grade with additional hardness-control and processing requirements. B7 and B7M should not be substituted without engineering and purchaser approval.
Do B7M stud bolts automatically comply with NACE MR0175?
No. B7M is often used in controlled-hardness specifications, but NACE MR0175/ISO 15156 compliance depends on the stated edition, service environment, material condition and project requirements.
Which nuts are used with B7M studs?
ASTM A194 Grade 2HM heavy hex nuts are commonly specified. Confirm nut dimensions, finish, hardness, testing and quantity in the purchase order.
Can B7M stud bolts be PTFE coated?
A fluoropolymer coating may be supplied when approved, but the coating process, temperature limit, thickness, friction behaviour and project sour-service restrictions must be reviewed before manufacture.
Related stud bolt products
Reference standards
Material requirements are controlled by ASTM A193/A193M. Matching heavy hex nut requirements are specified separately under ASTM A194/A194M when applicable. Thread form and stud dimensions may reference ASME B1.1 and ASME B18.31.2, subject to the purchase order. Always state the required edition instead of assuming the latest edition applies to an existing project.
Request a technical quotation
Send your flange bolting schedule, bill of materials, drawing or project specification. SASA FLANGE will review the grade, nuts, threads, dimensions, finish, documentation and delivery requirements before quotation.
