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    2. Grade 8T Nuts

    ASTM A194 Grade 8T Heavy Hex Nuts — UNS S32100

    High-temperature stainless steel nuts for industrial and refinery systems.

    ASTM A194/A194M Grade 8T Nuts are stabilized stainless steel fasteners developed for thermal processing and high-temperature industrial environments. These nuts provide excellent oxidation resistance and long-term durability. They are widely used with ASTM A193/A193M stud bolts and ASTM A320/A320M fastening systems in refinery and petrochemical industries. ASTM A563M and ASTM F2437/F2437M standards are also commonly referenced.

    ASTM A194/A194M GradeA194/A194M Grade 8T Chemical Requirements

    Grade Description
    and
    UNS Designation    		 C Mn P SE Si Cr Ni Ti N
    ASTM A194/A194M Grade 8T (321) S32100 0.08 2.00 0.045 0.030 1.00 17.0-19.0 9.0-12.0 5 x (C+N) min - 0.70 max 0.10
    • (A) Total aluminum, soluble and insoluble.
    • (B) Maximum, unless minimum or range is indicated.
    • (C) Where ellipses (...) appear in this table there is no requirement.

    ASTM A194/A194M GradeA194/A194M Grade 8T Hardness Requirements

    Grade and Type Completed Nuts
    Brinell Hardness Rockwell Hardness
    C Scale B Scale
    ASTM A194/A194M Grade 8T 126 to 300 32 max 60 min

    ASTM A194/A194M GradeA194/A194M Grade 8T Proof Load Requirements (Inch Series)

    Nominal Size, in. Threads per Inch Stress Area in. 2 Proof Load, lbf A
    Grade 8T
    Heavy HexH HexI
    1/4 20 0.0316 2 540 2 380
    5/16 18 0.0524 4 190 3 930
    3/8 16 0.0774 6 200 5 810
    7/16 14 0.1063 8 500 7 970
    1/2 13 0.1419 11 350 10 640
    9/16 12 0.182 14 560 13 650
    5/8 11 0.226 18 080 16 950
    3/4 10 0.334 26 720 25 050
    7/8 9 0.462 36 960 34 650
    1 8 0.606 48 480 45 450
    11/8 8 0.790 63 200 59 250
    11/4 8 1.000 80 000 75 000
    13/8 8 1.233 98 640 92 450
    11/2 8 1.492 119 360 111 900
    • (A) See limit for proof load test in 8.2.2.1. The proof load for jam nuts shall be 46 % of the tabulated load.
    • (B) Based on proof stress of 130 000 psi.
    • (C) Based on proof stress of 120 000 psi.
    • (D) Based on proof stress of 150 000 psi.
    • (E) Based on proof stress of 135 000 psi.
    • (F) Based on proof stress of 175 000 psi.
    • (G) Based on proof stress of 150 000 psi.
    • (H) Based on proof stress of 80 000 psi.
    • (I) Based on proof stress of 75 000 psi.

    ASTM A194/A194M GradeA194/A194M Grade 8T Proof Load Requirements (Metric Series)

    Nominal Size, mm Threads Pitch Stress Area mm 2 Proof Load, kNA
    Grade 8T
    Heavy HexH HexI
    M6 1.0 20.1 11.1 10.4
    M8 1.25 36.6 20.1 18.8
    M10 1.50 58.0 31.9 29.9
    M12 1.75 84.3 46.4 43.4
    M14 2.0 115.0 63.3 59.2
    M16 2.0 157.0 86.4 80.9
    M20 2.5 245.0 134.8 126.2
    M22 2.5 303.0 166.7 156.0
    M24 3.0 353.0 194.2 181.8
    M27 3.0 459.0 252.5 236.4
    M30 3.5 561.0 308.6 288.9
    M36 4.0 817.0 449.4 420.8
    • (A) See limit for proof load test in 8.2.2.1. The proof load for jam nuts shall be 46 % of the tabulated load.
    • (B) Based on proof stress of 895 MPa.
    • (C) Based on proof stress of 825 MPa.
    • (D) Based on proof stress of 1035 MPa.
    • (E) Based on proof stress of 930 MPa.
    • (F) Based on proof stress of 1205 MPa.
    • (G) Based on proof stress of 1035 MPa.
    • (H) Based on proof stress of 550 MPa.
    • (I) Based on proof stress of 515 MPa.

    Related Grades & References

    Grade 8T is titanium-stabilised Type 321 austenitic stainless (UNS S32100), offering intergranular-corrosion resistance after exposure to sensitization-range temperatures (425-815°C), preferred for high-temperature service paired with A193 B8T studs. Class 1A variant: Grade 8TA. The niobium-stabilised alternative is Grade 8C (347). For standard 304 service: Grade 8; for 316 service: Grade 8M. For low-C nitrogen-strengthened 304LN: Grade 8LN. Dimensions: ASME B18.2.2 heavy hex. Reference: ASTM A194 PDF · A194 hub.

    International Equivalents

    StandardRegionNotes
    ASTM A194-8TAUSAClass 1A finished condition variant
    BS EN 10088-3 1.4541EUTitanium-stabilised austenitic 321
    DIN X6CrNiTi18-10GermanyMaterial number 1.4541 (321)
    AFNOR Z6CNT18-10FranceTi-stabilised austenitic stainless
    JIS SUS321JapanType 321 Ti-stabilised austenitic
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