ASTM A193 Grade B8M Class 1 (316 Stainless)
316 stainless bolting with molybdenum for chloride and pitting resistance — offshore, marine, chemical and coastal plant fasteners.
What A193 B8M Class 1 is.
ASTM A193 Grade B8M is the 316 stainless steel bolting grade. The 2 to 3 percent molybdenum in 316 sharply improves resistance to pitting and crevice corrosion in chloride environments, which is why B8M is specified for offshore platforms, coastal refineries, desalination and chemical plants where B8 would pit.
Class 1 is solution treated for maximum corrosion resistance and ductility; Class 2 is strain hardened for strength, up to 110 ksi in small diameters. We machine both from certified 316 and 316L bar with full heat traceability.
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 | 16.0 | 18.0 |
| Nickel | Ni | 10.0 | 14.0 |
| Molybdenum | Mo | 2.00 | 3.00 |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 4D, min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| Class 1 — all diameters | 75 | 30 | 30 | 50 | 223 HBW / 96 HRB |
| Class 1A (B8MA) — all diameters | 75 | 30 | 30 | 50 | 192 HBW / 90 HRB |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Class 1 sizes ¾ in. and smaller may be 241 HBW / 100 HRB. Strain-hardened Class 2, 2B and 2C properties are on the B8M Class 2 page.
Specifications that apply.
How A193 B8M Class 1 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
A193 B8M Class 1 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8M Class 1, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8M?
B8M is A193's 316 stainless grade. Compared with the 304 used for B8, 316 carries more nickel and adds molybdenum, which stabilises the passive film against chloride attack. That single change moves the alloy from fresh-water service into seawater, brine and many acid environments. Like B8, it is supplied in Class 1 (solution treated) and Class 2 (strain hardened), and the strain-hardened strengths are slightly lower than B8's because 316 work-hardens less.
When 316 is the right call
Specify B8M anywhere chlorides are present: marine and coastal atmospheres, seawater and brackish cooling water, deicing-salt exposure, chlorinated process streams and many organic acid services. It is also the more common stainless in pharmaceutical and food-contact equipment that is cleaned with chlorine-based sanitisers. For higher chloride concentrations or temperatures, duplex and super duplex grades take over.
Nuts, washers and galling
Pair B8M studs with ASTM A194 Grade 8M nuts and 316 washers so the whole joint shares one corrosion potential. Austenitic threads gall under load without lubrication; we supply anti-seize, PTFE-coated studs or silver-plated nuts to suit the service.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade symbol B8M and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- PMI, ferrite and intergranular corrosion testing (ASTM A262) arranged on request
Recent A193 B8M Class 1 jobs.
ASTM A193 Grade B8M Class 2 (316 Strain Hardened)
316 stainless bolting cold worked after solution treatment — 110 ksi tensile in ¾ in. and under, with B8M2 and B8M3 classes for diameters to 3 in. and beyond.
ASTM A193 / ASME SA-193ASTM A193 Grade B8 Class 1 (304 Stainless)
304 stainless bolting — Class 1 for corrosion resistance and cryogenic-to-1500 °F service, Class 2 strain hardened to 125 ksi for strength.
ASTM A194 / ASME SA-194ASTM A194 Grade 8M (316 Stainless)
316 stainless heavy hex nut for B8M studs — molybdenum-bearing for chloride and marine service, 80 ksi proof load.