ASTM A194 Grade 16
The Cr-Mo-V heavy hex nut that matches A193 B16 studs — for steam turbine and high-temperature steam flange bolting.
What A194 16 is.
ASTM A194 Grade 16 is a quenched-and-tempered nut in the same chromium-molybdenum-vanadium steel as A193 B16. It is tempered at 1200 °F minimum, hardened to 24 to 35 HRC and proof-load rated at 175 ksi for heavy hex nuts, so a B16 stud can be paired with a nut that relaxes at the same rate at temperature.
Grade 16 is specified on steam turbine casings, HP steam flanges and hot valve bonnets in power generation. We machine it from certified Cr-Mo-V bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.36 | 0.47 |
| Manganese | Mn | 0.45 | 0.70 |
| Phosphorus | P | — | 0.035 |
| Sulfur | S | — | 0.040 |
| Silicon | Si | 0.15 | 0.35 |
| Chromium | Cr | 0.80 | 1.15 |
| Molybdenum | Mo | 0.50 | 0.65 |
| Vanadium | V | 0.25 | 0.35 |
| Aluminum (total) | Al | — | 0.15 |
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 | 175 | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
| Hex (finished pattern), all sizes | 150 | 248 HBW / 24 HRC | 327 HBW / 35 HRC |
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.
Specifications that apply.
How A194 16 ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 16 fasteners we make.
Every item is manufactured to your drawing or standard in A194 16, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 16?
Grade 16 is the Cr-Mo-V nut in A194, added so that B16 studs could be paired with a nut of the same alloy rather than a Grade 4 or 7. The vanadium and higher molybdenum give it the same creep and relaxation resistance as the stud, and the 1200 °F minimum temper means it will not soften in service below that temperature. Hardness and proof load match 2H and 7.
Grade 16 or Grade 7 for B16 studs?
B16 studs are normally supplied with Grade 16 nuts, or Grade 7 where the purchaser allows. Grade 7 is more widely stocked and is adequate for most joints below 900 °F. For the hottest steam turbine and superheater bolting, where the joint must hold clamp load for years, specify Grade 16 so the nut relaxes no faster than the stud.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 16, or 16B 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
Recent A194 16 jobs.
ASTM A193 Grade B16
Vanadium-strengthened Cr-Mo bolting that holds its strength where B7 starts to relax — steam turbines, HP steam flanges and hot valve bonnets.
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.