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ASME B18.2.4.1M 8S Hex Nut
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Name: Xiamen ASME B18.2.4.1M 8S Hex Nut
Standard: ASME B18.2.4.1M
Material: A193 Gr. 8S
Size: M12
Surface: Natural color
Standard: ASME B18.2.4.1M
Material: A193 Gr. 8S
Size: M12
Surface: Natural color
Quantity
This ASME B18.2.4.1M 8S Hex Nut follows the U.S. standard ASME B18.2.4.1M all-metal locking design.
Material: high-temperature, high-strength A193 Gr. 8S alloy steel.
Material: high-temperature, high-strength A193 Gr. 8S alloy steel.
Size: M12, giving broad interchangeability.
Finish: natural colour, no plating residue.
Tensile strength ≥ 860 MPa, continuous service to 450 °C, 500 h salt-spray without red rust.
Typical uses: petro-chemical valves, pressure vessels, wind-tower flanges and other heavily loaded, vibrating joints.
Finish: natural colour, no plating residue.
Tensile strength ≥ 860 MPa, continuous service to 450 °C, 500 h salt-spray without red rust.
Typical uses: petro-chemical valves, pressure vessels, wind-tower flanges and other heavily loaded, vibrating joints.
How grade 8S differs from the rest ？
Grade 8S (ASTM A193 B8S) is not “just one more stainless number”; it is a high-strength austenitic fastener material developed for “strong vibration + medium-high temperature + chloride”.
Grade 8S (ASTM A193 B8S) is not “just one more stainless number”; it is a high-strength austenitic fastener material developed for “strong vibration + medium-high temperature + chloride”.
Place it beside the common ASTM A193 family members—8A (B8), 8B (B8C), 8C (B8M)—and their best workplaces become obvious.
The comparison below uses ASME B18.2.4.1M 8S Hex Nut as the reference to help engineers choose quickly.
The comparison below uses ASME B18.2.4.1M 8S Hex Nut as the reference to help engineers choose quickly.
1. Chemistry – “with or without nitrogen” decides corrosion resistance and strength
- ASME B18.2.4.1M 8S Hex Nut ≈ UNS S21800 (Nitronic 60): ~8 % Ni, 17 % Cr, 7 % Mn, 0.2 % N; Mn-N synergy raises work-hardening rate.
- 8A/B8 = 304 type, 8B/B8C = 347 type (Nb stabilised), 8C/B8M = 316 type (2–3 % Mo against chloride pitting).
Thus 8S does not have the highest Cr-Ni, yet the Mn-N recipe doubles yield strength while keeping the austenitic structure non-magnetic.
- ASME B18.2.4.1M 8S Hex Nut ≈ UNS S21800 (Nitronic 60): ~8 % Ni, 17 % Cr, 7 % Mn, 0.2 % N; Mn-N synergy raises work-hardening rate.
- 8A/B8 = 304 type, 8B/B8C = 347 type (Nb stabilised), 8C/B8M = 316 type (2–3 % Mo against chloride pitting).
Thus 8S does not have the highest Cr-Ni, yet the Mn-N recipe doubles yield strength while keeping the austenitic structure non-magnetic.
2. Mechanical properties – “high strength + anti-galling” is what 8S sells
In solution-treated condition ASME B18.2.4.1M 8S Hex Nut offers Rp0.2 ≥ 380 MPa, Rm ≥ 720 MPa, 50–80 % higher than Class-1 solution-treated 8A/8C/8M.
Its high work-hardening exponent raises surface hardness above 250 HV after cold threading, so:
- Galling resistance ≈ 4 × that of 316;
- Retains 70 % of room-temperature strength up to 315 °C, whereas ordinary 304/316 have dropped to 55–60 % by 300 °C.
In solution-treated condition ASME B18.2.4.1M 8S Hex Nut offers Rp0.2 ≥ 380 MPa, Rm ≥ 720 MPa, 50–80 % higher than Class-1 solution-treated 8A/8C/8M.
Its high work-hardening exponent raises surface hardness above 250 HV after cold threading, so:
- Galling resistance ≈ 4 × that of 316;
- Retains 70 % of room-temperature strength up to 315 °C, whereas ordinary 304/316 have dropped to 55–60 % by 300 °C.
3. Corrosion resistance – a “chlorides + wear” compromise
ASME B18.2.4.1M 8S Hex Nut contains no Mo; PREN ≈ 21, lower than 316’s 26, so long-term marine exposure still needs coating.
However, its resistance to the combined attack of crevice corrosion plus fretting exceeds 316 because the nitride film is harder and less easily scratched.
ASME B18.2.4.1M 8S Hex Nut contains no Mo; PREN ≈ 21, lower than 316’s 26, so long-term marine exposure still needs coating.
However, its resistance to the combined attack of crevice corrosion plus fretting exceeds 316 because the nitride film is harder and less easily scratched.
4. Price & availability – “expensive but saves shutdowns”
8S bar stock costs ≈ 2.2 × 304 and 1.6 × 316.
Yet one galling event that forces a pump back to the shop can incur rigging fees 100 times the price of the nut; hence petrochemical plants call the ASME B18.2.4.1M 8S Hex Nut the “Insurance Nut”.
8S bar stock costs ≈ 2.2 × 304 and 1.6 × 316.
Yet one galling event that forces a pump back to the shop can incur rigging fees 100 times the price of the nut; hence petrochemical plants call the ASME B18.2.4.1M 8S Hex Nut the “Insurance Nut”.
Real-world selection examples
- Offshore water-injection centrifugal pump: 316L casing + B8M fasteners was standard, but the pump had to be opened every six months to change seals and the thread-galling rate was 30 %. After switching to ASME B18.2.4.1M 8S Hex Nut, four openings in two years recorded zero galling, saving 36 offshore hours and USD 1.2 M in lost production.
- Offshore water-injection centrifugal pump: 316L casing + B8M fasteners was standard, but the pump had to be opened every six months to change seals and the thread-galling rate was 30 %. After switching to ASME B18.2.4.1M 8S Hex Nut, four openings in two years recorded zero galling, saving 36 offshore hours and USD 1.2 M in lost production.
- 250 °C steam flange on a power-plant turbine: B16 alloy nuts with MoS₂ coating were used; vibration blew off the coating and galling occurred. Replacing them with ASME B18.2.4.1M 8S Hex Nut eliminated the coating, allows dry disassembly, and matches the 304 mating part’s thermal expansion, cutting preload loss by 25 %.
- Gear-box inspection cover on high-speed trains: A2-70 stainless bolts suffered galling within three months under winter switch de-icing salt. After changing to ASME B18.2.4.1M 8S Hex Nut plus matching bolts, no replacement was needed through two overhaul cycles (six years) and maintenance man-hours fell 70 %.
Take-away
High chloride → pick 8C/8M.
Frequent disassembly + fear of galling + medium-high temp vibration → pick ASME B18.2.4.1M 8S Hex Nut.
Ordinary corrosion at room temperature → 8A/8B is most economical.
High chloride → pick 8C/8M.
Frequent disassembly + fear of galling + medium-high temp vibration → pick ASME B18.2.4.1M 8S Hex Nut.
Ordinary corrosion at room temperature → 8A/8B is most economical.
Treat it as the “anti-galling stainless lock nut”; wherever you must disassemble repeatedly, cannot use lubricant or adhesive, and must stay non-magnetic, it is the most worry-free safety bolt you can buy.
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