| Standard | ASTM A320 · A320M Grade L7 / Grade L7M |
|---|---|
| Material | ASTM A320 Grade L7 / L7M chromium-molybdenum alloy steel |
| Strength Grade | L7 / L7M |
| Size Range | M12-M64 / 1/2"-4" |
| Surface Treatment | Plain / Black Oxide / Phosphate / PTFE Coated / Zinc Plated |
Product Description
ASTM A320/A320M Grade L7 and L7M stud bolts are quenched-and-tempered chromium-molybdenum alloy steel fasteners for low-temperature pressure service. They are used in flanges, valves, pressure vessels, process piping and LNG-related equipment when the governing specification requires impact toughness at a defined test temperature.
L7 is the higher-strength general low-temperature grade and is paired with impact-tested ASTM A194 Grade 7L heavy hex nuts when the low-temperature qualification must extend to the nut. L7M is a lower-strength, controlled-maximum-hardness grade paired with ASTM A194 Grade 7M nuts. The M grade does not by itself prove sour-service compliance; any NACE MR0175 / ISO 15156 or NACE MR0103 / ISO 17945 requirement must be invoked separately.
ASTM A320 L7 should not be treated as identical to ASTM A193 B7. The alloy family may be similar, but A320 carries the low-temperature service and impact-testing route. The RFQ should state minimum design temperature, required Charpy test temperature and acceptance values, diameter, length, thread, coating, nut grade and documentation.
| Product type | ASTM A320 L7 and L7M low-temperature stud bolts |
|---|---|
| Standard | ASTM A320/A320M Grade L7 / Grade L7M |
| Material | Quenched and tempered chromium-molybdenum alloy steel |
| L7 selection | Higher-strength general low-temperature bolting; paired with impact-tested ASTM A194 Grade 7L nuts |
| L7M selection | Lower-strength, controlled-maximum-hardness bolting; commonly paired with ASTM A194 Grade 7M nuts |
| Impact testing | Charpy test temperature and acceptance values must follow the applicable edition, diameter and purchase order |
| Size range | M12-M64 / 1/2 in-4 in |
| Thread type | UNC / 8UN / metric thread by flange schedule or customer drawing |
| Surface finish | Plain / Black oxide / Phosphate / PTFE coated / Zinc plated |
| Sour-service qualification | NACE MR0175 / ISO 15156 or NACE MR0103 / ISO 17945 only when explicitly invoked and verified |
| Documentation | MTC, heat-treatment record, impact report, tensile or hardness report, dimensions and heat traceability as specified |
| Parameter | M4 | M5 | M6 | M7 | M8 | M10 | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 | M30 | M33 | M36 | M39 | M42 | M45 | M48 | M52 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P | 0.7 | 0.8 | 1 | 1 | 1|1.25 | 1.25|1.5 | 1.25|1.5|1.75 | 1.5|2 | 1.5|2 | 1.5|2.5 | 1.5|2.5 | 1.5|2.5 | 2|3 | 2|3 | 2|3.5 | 2|3.5 | 3|4 | 3|4 | 3|4.5 | 3|4.5 | 3|5 | 3|5 |
| b1 | 5 | 6.5 | 7.5 | 9 | 10 | 12 | 15 | 18 | 20 | 22 | 25 | 28 | 30 | 35 | 38 | 42 | 45 | 50 | 52 | 58 | 60 | 65 |
| ds/max | 4 | 5 | 6 | 7 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 27 | 30 | 33 | 36 | 39 | 42 | 45 | 48 | 52 |
Engineering references
Selection
L7 and L7M studs are used in cold process lines, valves and flange packages when project impact requirements are defined. Confirm minimum design temperature, Charpy test temperature, nut grade, coating and lubricant before production.
Oil and gas fastenersCompare the ASTM A320 low-temperature route with ASTM A193 high-temperature grades, stainless and nickel alloys before procurement.
Fastener material selection guideAssembly
Manufacturing
FAQ
L7 is the higher-strength general low-temperature alloy-steel bolting grade. L7M has lower mechanical strength, controlled maximum hardness and grade-specific testing. Both remain subject to the impact requirements of the applicable ASTM A320 edition and purchase order.
ASTM A320 L7 studs pair with impact-tested ASTM A194 Grade 7L heavy hex nuts when low-temperature nut qualification is required. L7M studs pair with controlled-hardness ASTM A194 Grade 7M nuts.
They should not be treated as identical. Although both are chromium-molybdenum alloy-steel grades, ASTM A320 L7 follows a low-temperature service and impact-testing route. Substitution requires engineering review of temperature, impact, marking and documentation requirements.
No. L7M provides grade-specific hardness control, but the applicable NACE or ISO standard, edition, environmental limits and inspection scope must be stated and verified separately.
Send grade, diameter, overall length, thread, minimum design temperature, required Charpy test temperature and acceptance values, coating, nut grade, certificate scope and quantity.
Send the design temperature, grade, diameter, length, thread, coating, nut pairing, impact-test requirement, quantity and certificate scope. We can quote L7 with Grade 7L or L7M with Grade 7M matched sets.
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