Description
Chromium-molybdenum bolting for pressure service
ASTM A193 Grade B7 Alloy Steel Heavy Hex Bolts
ASTM A193 Grade B7 alloy steel heavy hex bolts are quenched-and-tempered chromium-molybdenum fasteners widely specified for high-pressure, elevated-temperature and special-purpose industrial bolted joints.
What are ASTM A193 B7 heavy hex bolts?
ASTM A193/A193M Grade B7 covers heat-treated chromium-molybdenum alloy steel bolting used with pressure vessels, valves, flanges, fittings and other critical equipment. Although fully threaded studs are common in flange joints, the same grade can be manufactured as headed heavy hex bolts when the equipment drawing or bill of materials requires that configuration.
The A193 material grade and the bolt geometry are separate ordering elements. State Grade B7 for material and mechanical properties, then define the heavy hex head, ASME B18.2.1 dimensional basis, thread series, length, nut grade, washer, coating and inspection requirements.
Key procurement advantages
ASTM A193 Grade B7 Alloy Steel Heavy Hex Bolts specifications
| Bolting standard | ASTM A193/A193M, ordered edition |
|---|---|
| Grade | B7 |
| Material | Quenched-and-tempered chromium-molybdenum alloy steel |
| Head style | Heavy hex head |
| Head dimensions | ASME B18.2.1 or project drawing when specified |
| Thread system | UNC, UNF or 8UN to ASME B1.1 as ordered |
| Typical supply range | 1/2 through 4 in. diameter; special sizes and lengths subject to manufacturing review |
| Compatible nut | ASTM A194/A194M Grade 2H heavy hex nut when specified |
| Washer | Hardened washer grade and dimensions selected by the joint design |
| Finish / coating | Plain, black oxide, zinc, hot-dip galvanized, PTFE or project coating after technical review |
| Documentation | EN 10204 3.1 MTC, heat traceability, hardness and mechanical-test records as ordered |
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 B7 Alloy Steel Heavy Hex Bolts | When to review another grade |
|---|---|---|
| Service | High pressure and elevated temperature | A320 L7 for verified low-temperature toughness |
| Material basis | ASTM A193 Grade B7 Cr-Mo alloy steel | F3125 A490 for structural steel joints |
| Common nut | ASTM A194 Grade 2H heavy hex | Nut grade changes with the selected bolting specification |
| Product form | Heavy hex bolt made to the ordered geometry | Stud bolts remain a separate and common A193 configuration |
Matching nuts, washers and coatings
ASTM A194 Grade 2H heavy hex nuts are a common match for Grade B7. The washer grade, thread series and coating must suit the joint design. For coated assemblies, confirm dimensional allowance, nut overtapping where applicable, lubrication and installation torque rather than applying an unverified generic torque value.
Typical applications
| Industry | Typical duty | Why this grade is specified |
|---|---|---|
| Oil and gas | Valves, skids and pressure-containing equipment | Recognized Cr-Mo pressure bolting grade |
| Petrochemical | Process equipment and selected flange connections | Strength at elevated service temperature |
| Power generation | Equipment casings and auxiliary systems | Heat-treated alloy steel performance |
| Industrial machinery | High-load bolted assemblies | Heavy hex bearing area and project-specific sizing |
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.
Chemistry, heat treatment and mechanical results linked to the heat.
Grade compliance verified to the ordered diameter and product requirements.
Pitch diameter, thread class and fit checked with calibrated gauges.
Positive material identification and third-party inspection available 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 are ASTM A193 B7 heavy hex bolts?
They are headed chromium-molybdenum alloy steel bolts manufactured to Grade B7 material requirements with a heavy hex head defined by the purchase order.
Are B7 heavy hex bolts the same as B7 stud bolts?
No. They share the A193 B7 material grade, but a heavy hex bolt has an integral head while a stud is headless and commonly threaded along all or part of its length.
Which nut is normally paired with a B7 bolt?
ASTM A194 Grade 2H heavy hex nuts are commonly specified. The final nut, washer, thread and coating combination must follow the equipment or piping specification.
Is Grade B7 suitable for low-temperature service?
B7 is primarily specified for high-temperature or high-pressure service. Where verified low-temperature impact toughness is required, ASTM A320 Grade L7 is commonly considered instead.
Can B7 bolts be supplied with PTFE coating?
Yes, when the coating system, thickness, nut allowance, lubrication and service compatibility are defined and technically approved.
Request a heavy hex bolt quotation
Send the standard, grade, drawing, size, assembly, service condition, quantity and documentation requirements for technical review.
