ASTM A320 Grade L7M
Controlled-hardness L7 for cold sour service — 22 HRC max, NACE MR0175 compliant, Charpy tested at −100 °F.
What A320 L7M is.
ASTM A320 Grade L7M combines the low-temperature toughness of A320 with the hardness limit sour service demands. It is the same Cr-Mo steel as L7, tempered to a maximum of 235 HBW, tensile strength 100 ksi minimum, and Charpy tested at −100 °F. Like B7M, every piece is hardness tested.
L7M is specified for sour gas plants, cold-climate wellheads and any H₂S-bearing system with a low design temperature. We produce it from certified bar with the machine-thread-then-temper sequence and 100 percent hardness inspection the grade requires.
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. For L7M a minimum carbon of 0.28 % is permitted (AISI 4130/4130H allowed) provided the tensile properties are met.
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 | 100 | 80 | 18 | 50 | 235 HBW / 99 HRB (200 HBW / 93 HRB min) |
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. L7M: 235 HBW / 99 HRB max and 200 HBW / 93 HRB min, tested on every piece.
| Grade | Test temperature | Specimen | Energy, average of three (ft·lbf) | Energy, single specimen min (ft·lbf) |
|---|---|---|---|---|
| L7M | −100 °F (−73 °C) | 10 × 10 mm | 20 | 15 |
| L7M | −100 °F (−73 °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.
Specifications that apply.
How A320 L7M 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 L7M fasteners we make.
Every item is manufactured to your drawing or standard in A320 L7M, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A320 L7M?
L7M is Grade L7 with the modified temper that keeps hardness at or below 235 HBW, the threshold NACE MR0175 sets for resistance to sulfide stress cracking. Minimum tensile strength drops to 100 ksi and yield to 80 ksi, in exchange for a steel that can live in wet H₂S. The Charpy test temperature is −100 °F rather than L7's −150 °F, reflecting the slightly lower toughness margin of the softer temper.
Choosing between L7M and B7M
The two grades are the same steel at the same hardness; the difference is that L7M carries a low-temperature impact test. If the minimum design metal temperature is below −20 °F, or the piping specification invokes A320, use L7M. Otherwise B7M is the standard sour-service grade and is usually more readily available in stock sizes.
Nuts for L7M
Use ASTM A194 Grade 7M nuts, which share the 235 HBW cap and a 150 ksi proof load, and ask for them to be impact tested with the studs when the order requires it. Grade 2HM is the carbon steel alternative where the specification permits.
Testing, certification and marking
- 100 percent hardness testing on the finished product
- Tensile and Charpy V-notch impact tested per heat-treat lot at −100 °F
- Grade symbol L7M and manufacturer's identification on every piece
- EN 10204 3.1 material test report; NACE compliance statement, 3.2 witness and PMI on request
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.
ASTM A193 / ASME SA-193ASTM A193 Grade B7M
B7 tempered to 22 HRC max for sour service — the NACE MR0175 bolting grade for wellheads, sour gas and H₂S process piping.
ASTM A194 / ASME SA-194ASTM A194 Grade 7M
Controlled-hardness Cr-Mo nut for sour service at temperature — 235 HBW max, NACE MR0175, for B7M and L7M studs.