ASTM A320 Grade L7
The low-temperature twin of B7 — same 4140 Cr-Mo steel, same 125 ksi strength, but impact tested at −150 °F for cryogenic and cold-climate service.
What A320 L7 is.
ASTM A320 Grade L7 is the alloy-steel bolting grade for low-temperature service. It is made from the same quenched-and-tempered chromium-molybdenum steel as A193 B7 and meets the same strength requirements, with one addition: every heat-treat lot over ½ in. is Charpy impact tested at −150 °F to prove the steel stays tough when it is cold.
L7 is the standard grade for LNG, ethylene, ammonia and refrigeration systems, and for outdoor plants in northern climates where a brittle stud on a winter start-up is a real risk. We manufacture L7 studs and bolts from certified bar, heat treat after threading and impact test each lot through our laboratory partners.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.38 | 0.48 |
| Manganese | Mn | 0.75 | 1.00 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Chromium | Cr | 0.80 | 1.10 |
| Molybdenum | Mo | 0.15 | 0.25 |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 2 in., min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| 2½ and under | 125 | 105 | 16 | 50 | 321 HBW / 35 HRC |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Table 1 lists L7 to 2½ in.; footnote A says the limit reflects the sizes commonly available that meet the properties, not an absolute ceiling.
| Grade | Test temperature | Specimen | Energy, average of three (ft·lbf) | Energy, single specimen min (ft·lbf) |
|---|---|---|---|---|
| L7 | −150 °F (−101 °C) | 10 × 10 mm | 20 | 15 |
| L7 | −150 °F (−101 °C) | 10 × 7.5 mm | 16 | 12 |
Values per ASTM A320/A320M-26, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Bolting ½ in. and under is exempt from impact testing unless S1 is specified.
Specifications that apply.
How A320 L7 ships from Houston.
- Full-thread studs and stud bolts
- Double-end and tap-end studs
- Hex and heavy hex bolts
- Socket head cap screws
- Threaded rod (cut and rolled thread)
- Machined components from certified bar
A320 L7 fasteners we make.
Every item is manufactured to your drawing or standard in A320 L7, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 L7?
ASTM A320 is the low-temperature counterpart to A193. Grade L7 is its chromium-molybdenum member, and its chemistry, heat treatment and strength are the same as A193 B7's. What A320 adds is a mandatory Charpy V-notch impact test on each lot at −150 °F, with a 20 ft·lbf average and 15 ft·lbf single-specimen minimum. That test is the buyer's evidence that the steel will not fracture in a brittle manner at the design minimum temperature.
Because the underlying steel is identical, L7 can be dual-certified to A193 B7. Many stocking programmes carry L7 for that reason: it satisfies both specifications.
L7 versus L7M and L43
L7M is L7 tempered to a 235 HBW maximum for sour service, impact tested at −100 °F. L43 is a 4340 nickel-chromium-moly steel, impact tested at −150 °F, with better hardenability for large diameters. L7 covers the majority of low-temperature flange bolting; move to L7M when H₂S is present and to L43 when diameters exceed 2½ inches.
Nuts for low-temperature service
A320 requires nuts to ASTM A194 Grade 7 (or A320 L43 / L73), and A320 clauses 1.4 and 10.1 require the nut material to be impact tested as well, with the nuts marked L. Ask for the nuts to be certified with the studs so the whole joint carries the same low-temperature pedigree.
Testing, certification and marking
- Tensile, hardness and Charpy V-notch impact tested per heat-treat lot
- Grade symbol L7 and manufacturer's identification on every piece
- EN 10204 3.1 material test report with impact values and test temperature; 3.2 witness available
- Dual certification to A193 B7 on request
Recent A320 L7 jobs.
ASTM A320 Grade L7M
Controlled-hardness L7 for cold sour service — 22 HRC max, NACE MR0175 compliant, Charpy tested at −100 °F.
ASTM A193 / ASME SA-193ASTM A193 Grade B7
The workhorse alloy-steel bolting grade for flanges, valves and pressure equipment — 125 ksi tensile, quenched and tempered 4140.
ASTM A194 / ASME SA-194ASTM A194 Grade 7
The Cr-Mo heavy hex nut — same 4140 steel as a B7 stud, rated for elevated temperature and the usual match for B16 and L7.