ASTM A194 Grade 2HM
The sour-service heavy hex nut — 2H tempered to 235 HBW max for NACE MR0175, matched to A193 B7M and A320 L7M studs.
What A194 2HM is.
ASTM A194 Grade 2HM is the controlled-hardness version of 2H. The same medium-carbon steel is tempered at a higher temperature to a hardness of 159 to 235 HBW, keeping it under the 22 HRC limit NACE MR0175 sets for wet H₂S service. Proof load stress is 150 ksi, still well above the 100 ksi strength of a B7M stud.
2HM nuts must be hardness tested on every piece. We machine them from certified bar and test 100 percent, then ship them certified with the matching B7M or L7M studs so the whole joint documents its sour-service compliance.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.40 | — |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.040 |
| Sulfur | S | — | 0.050 |
| Silicon | Si | — | 0.40 |
Values per ASTM A194/A194M-24, Tables 1, 2 and 5 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nut style and size (in.) | Proof load stress (ksi) | Hardness, min | Hardness, max |
|---|---|---|---|
| Heavy hex, all sizes | 150 | 159 HBW / 84 HRB | 235 HBW / 99 HRB |
| Hex (finished pattern), all sizes | 135 | 159 HBW / 84 HRB | 235 HBW / 99 HRB |
Values per ASTM A194/A194M-24, Tables 1, 2 and 5 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. 100 percent hardness testing; final stress relief after machining at not less than 50 °F below the original tempering temperature (1200 °F minimum in a furnace after an induction temper above 1300 °F).
Specifications that apply.
How A194 2HM ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 2HM fasteners we make.
Every item is manufactured to your drawing or standard in A194 2HM, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 2HM?
2HM is Grade 2H with a modified heat treatment. A higher tempering temperature brings the hardness down into a 159 to 235 HBW window, which places it below the sulfide-stress-cracking threshold for carbon steels. The proof load drops from 175 to 150 ksi, but because the matching B7M stud is also softer, the joint keeps its intended balance: the stud remains the weakest link.
Matching studs and nuts in sour service
Every component in a sour joint is exposed to the same environment, so studs and nuts both have to meet the hardness limit. Pair 2HM nuts with A193 B7M for normal temperatures and A320 L7M where low-temperature toughness is required. Grade 7M is the chromium-moly alternative for hotter sour lines.
Testing, certification and marking
- Every nut hardness tested (100 percent, A194 clause 8.1.3.1); proof-load tested per lot
- Grade symbol 2HM, or 2HMB on nuts machined from bar (ASTM A194 Table 7), and manufacturer's identification on one face of every nut
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Oversize tapping for coated studs and PTFE / zinc / hot-dip galvanized finishes available
ASTM 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 2H
The standard heavy hex nut for A193 B7 studs — quenched and tempered carbon steel, 175 ksi proof load, 24 to 35 HRC.
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.