Description
Hardness-controlled and impact-tested low-temperature bolting
ASTM A320 Grade L7M Alloy Steel Heavy Hex Bolts
ASTM A320 Grade L7M alloy steel heavy hex bolts combine low-temperature impact requirements with restricted hardness for pressure-equipment joints where the project specifies L7M.
What are ASTM A320 L7M heavy hex bolts?
Grade L7M is the hardness-controlled low-temperature counterpart within ASTM A320. It is selected for cold-service equipment where both impact toughness and restricted hardness are required, including some project-defined sour-service applications.
L7M does not create automatic NACE MR0175/ISO 15156 compliance. The order must state environmental limits, design minimum temperature, Charpy test temperature, hardness verification, product geometry, compatible Grade 7M nuts, washers, coating and all supplementary certification requirements.
Key procurement advantages
ASTM A320 Grade L7M Alloy Steel Heavy Hex Bolts specifications
| Bolting standard | ASTM A320/A320M, ordered edition |
|---|---|
| Grade | L7M |
| Material | Quenched-and-tempered alloy steel with restricted hardness and impact testing |
| 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, processing and testing subject to review |
| Compatible nut | ASTM A194/A194M Grade 7M heavy hex nut with required low-temperature testing |
| Impact testing | Charpy V-notch energy and test temperature to the ordered A320 and project requirements |
| Sour-service status | NACE MR0175/ISO 15156 compliance only when explicitly ordered and verified |
| Documentation | EN 10204 3.1 MTC, Charpy, hardness, heat-treatment, 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 A320 Grade L7M Alloy Steel Heavy Hex Bolts | When to review another grade |
|---|---|---|
| Hardness | Restricted for L7M | Higher permitted hardness for standard L7 |
| Low-temperature impact | Required to the ordered L7M basis | Also required for L7, with different grade requirements |
| Common nut | ASTM A194 Grade 7M with impact requirements | A194 Grade 4 or 7 commonly used with L7 |
| Sour-service claim | Requires project-specific NACE/ISO verification | L7 is not automatically a sour-service grade |
Matching nuts, washers and coatings
A complete L7M assembly normally uses ASTM A194 Grade 7M heavy hex nuts with the required low-temperature impact testing. Confirm washer grade, coating, lubricant, installation method and NACE/ISO documentation. The hardness and impact requirements must remain traceable to the finished bolt lot.
Typical applications
| Industry | Typical duty | Why this grade is specified |
|---|---|---|
| Sour gas processing | Specified cold-service pressure equipment | Restricted hardness plus impact-tested bolting |
| LNG and gas | Low-temperature skids with project hardness limits | L7M material and Grade 7M nut assembly |
| Refining | Selected cold H2S-bearing services | Project-controlled NACE/ISO verification where required |
| Chemical processing | Low-temperature pressure joints with hardness restrictions | Documented toughness, hardness and traceability |
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.
Finished-product hardness verification supplied when required by the ordered specification.
Energy, temperature, specimen and heat identification documented.
Processing route linked to the heat and finished bolt lot.
Environmental and certification requirements evaluated only against the stated order.
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 ASTM A320 Grade L7M?
L7M is a hardness-controlled, impact-tested alloy steel bolting grade for low-temperature service under ASTM A320/A320M.
How is L7M different from L7?
L7M has restricted hardness and different processing and mechanical requirements. Both grades require low-temperature impact testing to their ordered basis.
Does L7M automatically meet NACE MR0175?
No. NACE MR0175/ISO 15156 compliance must be explicitly specified and evaluated for the finished product, environment, hardness and complete bolting assembly.
Which nut matches an L7M heavy hex bolt?
ASTM A194 Grade 7M heavy hex nuts are commonly specified, with impact testing and documentation appropriate to the cold-service design.
What should an L7M RFQ include?
State the A320 edition, grade, diameter, length, thread, minimum design temperature, Charpy criteria, hardness and NACE/ISO requirements, nut and washer grades, coating, quantity and documents.
Request a heavy hex bolt quotation
Send the standard, grade, drawing, size, assembly, service condition, quantity and documentation requirements for technical review.
