Patriot Bolt machines ASTM A194 Grade 2HM heavy hex nuts for sour gas and other hydrogen sulfide service. 2HM is the controlled-hardness version of 2H: tempered at 1150 °F minimum to a maximum of 235 HBW so it resists sulfide stress cracking.
Every 2HM nut is hardness tested, as the specification requires. We make them alone or with matching B7M studs, and every order ships with mill test reports traceable to the heat.
A194 2HM Heavy Hex Nuts at a Glance
- Specification
- ASTM A194 / ASME SA194 Grade 2HM
- Material
- Medium-carbon steel, quenched and tempered at 1150 °F min
- Proof stress
- 150 ksi (heavy hex)
- Hardness
- 159–235 HBW, 100% tested
- Sour service
- NACE MR0175 / ISO 15156
- Matching stud
- A193 B7M
Why Engineers Specify A194 2HM Nuts
- Hardness limited. 235 HBW maximum keeps the nut under the 22 HRC limit NACE MR0175 sets for carbon steel in sour service.
- Every nut tested. A194 requires 100 percent hardness testing of 2HM.
- Matched to B7M. The nut and stud share the same hardness limit, so neither is the weak link in H2S.
A194 2HM Specifications
2HM has one hardness range for all sizes.
| Nut style | Proof stress | Hardness, min | Hardness, max |
|---|---|---|---|
| Heavy hex, all sizes | 150 ksi | 159 HBW / 84 HRB | 235 HBW / 99 HRB |
A194 2HM Chemical Composition
| Element | Weight % |
|---|---|
| Carbon | 0.40 min |
| Manganese | 1.00 max |
| Phosphorus | 0.040 max |
| Sulfur | 0.050 max |
| Silicon | 0.40 max |
2HM uses the 2H chemistry; the difference is the heat treatment and hardness limit. The mill test report for your heat is the controlling document.
Nut Styles
- Heavy hex nuts to ASME B18.2.2, the standard style for flange studs.
- Heavy hex jam nuts where a thinner nut is needed.
- Threads: UNC through 1 in and 8UN above 1 in, the usual flange series, or the thread on your drawing.
Applications and Industries
- Sour oil and gas: Wellhead, manifold and flowline flanges. See Oil & Gas.
- Gas processing and refining: Amine, sulfur recovery and sour water units. See Petrochemical & Refining.
- Offshore production: Process piping handling sour fluids.
Certification and Traceability
Patriot Bolt is ISO 9001:2015 certified. Each 2HM order includes mill test reports traceable to the heat, along with a certificate of conformance to the specification on your purchase order.
Nuts are marked 2HM, or 2HMB when machined from bar, with our identification on one face. Certifications include the hardness results required by the specification.
Compare 2HM with other bolting grades in our Fastener Materials Matrix.
A194 2HM Heavy Hex Nuts FAQ
Why use 2HM instead of 2H?
2H nuts can be harder than NACE MR0175 allows in sour service. 2HM is hardness limited to 235 HBW and every nut is tested.
Which studs go with 2HM nuts?
A193 B7M for normal temperatures and A320 L7M where low-temperature toughness is also needed.
Is the proof stress lower than 2H?
Yes. 2HM heavy hex nuts have a 150 ksi proof stress, compared with 175 ksi for 2H, because of the lower hardness.
Do you make matching B7M studs?
Yes. We machine B7M stud bolts, so the whole sour-service joint can come from one source.
Request a Quote
Send us the alloy, nut style, thread size, specification and quantity, or upload your drawing. Our team will confirm the material and lead time. Call (281) 581-0176 or request a quote.
Related: B7M stud bolts · A193 B7M fasteners hub · A194 2H nuts · All nuts