ASTM A193 Grade B8MLCuN Class 1B (254 SMO, UNS S31254)
254 SMO bolting — a 6 % Mo super austenitic with PREN above 42 for seawater, chlorinated cooling water and flue-gas scrubbers where 316 pits.
What A193 B8MLCuN Class 1B is.
ASTM A193 Grade B8MLCuN is bolting in UNS S31254, better known as 254 SMO. With 20 percent chromium, 18 percent nickel, 6 percent molybdenum, copper and 0.2 percent nitrogen, it resists chloride pitting and crevice corrosion at the level of the super duplex grades while remaining a fully austenitic, non-magnetic, weldable stainless.
A193 Class 1B gives it 80 ksi tensile and 35 ksi yield in any diameter. We supply B8MLCuN studs, bolts and nuts from certified A276 / A479 bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.020 |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.030 |
| Sulfur | S | — | 0.010 |
| Silicon | Si | — | 0.80 |
| Chromium | Cr | 19.5 | 20.5 |
| Nickel | Ni | 17.5 | 18.5 |
| Molybdenum | Mo | 6.0 | 6.5 |
| Copper | Cu | 0.50 | 1.00 |
| Nitrogen | N | 0.18 | 0.25 |
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 1B / 1D — all diameters | 80 | 35 | 30 | 40 | 223 HBW / 96 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 properties are on the B8MLCuN Class 2 page.
| Condition | Tensile strength, min (ksi) | Yield strength, min (ksi) | Elongation, min (%) | Reduction of area, min (%) |
|---|---|---|---|---|
| Condition A, annealed — all sizes | 95 | 44 | 35 | 50 |
Values per ASTM A276/A276M-17 Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How A193 B8MLCuN Class 1B ships from Houston.
- Full-thread studs and stud bolts
- Hex and heavy hex bolts
- Socket head cap screws
- Hex nuts in the same alloy
- Threaded rod
- Machined components from certified bar
A193 B8MLCuN Class 1B fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8MLCuN Class 1B, imperial or metric, with an EN 10204 3.1 certificate.
What is 254 SMO?
254 SMO (UNS S31254) was developed for seawater service. Its 6 percent molybdenum and 0.2 percent nitrogen give a pitting resistance equivalent number above 42, comparable to super duplex, and it resists crevice corrosion in warm seawater where 316 and even 2205 fail. Being fully austenitic it has better low-temperature toughness and weldability than duplex, and no magnetic response. A193 covers it as B8MLCuN with the same nitrogen-grade Class 1B strength as B8N and B8MN; A194 8MLCuN is the nut.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or alloy marking B8MLCuN and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
ASTM A193 Grade B8MLCuN Class 2 (254 SMO Strain Hardened)
6 percent molybdenum super-austenitic bolting cold worked to 110 ksi tensile in ¾ in. and under — seawater-grade corrosion resistance with Class 2 strength.
ASTM B691 barAL-6XN (UNS N08367)
The 6 % Mo super austenitic in nickel-alloy classification — PREN about 43 at minimum chemistry (typically about 45) for seawater, brine and chlorinated water — with 95 ksi tensile in the annealed bar.
ASTM A1082 bolting · ASTM A276 / A479 bar · ASTM A182 F53Super Duplex 2507 Stainless (UNS S32750)
25 Cr super duplex with a PREN above 40 — 116 ksi tensile and 80 ksi yield for the most aggressive seawater, sour and chloride bolting.