ASTM A194 Grade 8C (347 Stainless)
347 stainless heavy hex nut for B8C studs — stabilised against sensitisation for hot hydrogen, refinery and welded stainless service.
What A194 8C is.
ASTM A194 Grade 8C is the Type 347 nut that pairs with A193 and A320 Grade B8C studs. Niobium stabilisation keeps it free of intergranular corrosion after long hot service, and it is otherwise a standard austenitic nut machined from solution-annealed bar with an 80 ksi proof load and 126 to 300 HBW hardness.
Grade 8CA is the same nut solution treated after finishing. We machine both from certified 347 bar, with silver plating or oversize tapping to control galling.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.08 |
| Manganese | Mn | — | 2.00 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 17.0 | 19.0 |
| Nickel | Ni | 9.0 | 12.0 |
| Niobium (columbium) | Nb | 10 × C | 1.10 |
Values per ASTM A194/A194M-24, Tables 1, 2 and 3 (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 | 80 | 126 HBW / 60 HRB | 300 HBW / 32 HRC |
| Hex (finished pattern), all sizes | 75 | 126 HBW / 60 HRB | 300 HBW / 32 HRC |
| Grade 8CA (solution treated in the finished condition), all sizes | 80 heavy hex · 75 hex | 126 HBW / 60 HRB | 192 HBW / 90 HRB |
Values per ASTM A194/A194M-24, Tables 1, 2 and 3 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Jam nuts: 46 % of the tabulated proof load. Strain-hardened Grade 8 nuts (S1) are proof tested to 125 / 115 / 105 / 100 ksi heavy hex by size and hardness limits do not apply.
Specifications that apply.
How A194 8C ships from Houston.
- Heavy hex nuts (the default for pressure bolting)
- Finished hex nuts
- Jam nuts
- Custom and special nuts to drawing
A194 8C fasteners we make.
Every item is manufactured to your drawing or standard in A194 8C, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A194 Grade 8C?
Grade 8C is the 347 member of the A194 Grade 8 family. Niobium plus tantalum at ten times the carbon content ties up carbon so the nut does not sensitise when it sits at 800 to 1500 °F, which is exactly where 347 piping and B8C studs are used. Proof load and hardness are the same as Grade 8; the nut is non-magnetic, machined from solution-annealed bar.
Testing, certification and marking
- Hardness tested per lot; proof-load tested on request or where the specification requires it
- Grade symbol 8C, or 8CB 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 B8C Class 1 (347 Stainless)
347 stainless bolting stabilised with niobium against sensitisation — for hot hydrogen, refinery and welded stainless service between 800 and 1500 °F.
ASTM A194 / ASME SA-194ASTM A194 Grade 8T (321 Stainless)
321 stainless heavy hex nut for B8T studs — titanium stabilised for hot, cyclic and welded 321 equipment.
ASTM A194 / ASME SA-194ASTM A194 Grade 8 (304 Stainless)
304 stainless heavy hex nut for A193 and A320 B8 studs — solution treated, 80 ksi proof load, corrosion resistant from cryogenic to 1500 °F.