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    2. Grade 8C Nuts

    ASTM A194 Grade 8C Heavy Hex Nuts — UNS S34700

    Stabilized stainless steel nuts designed for elevated temperature and corrosion-resistant service.

    ASTM A194/A194M Grade 8C Nuts are stabilized stainless steel heavy hex nuts engineered for resistance to intergranular corrosion and elevated temperature service. These nuts are widely used in exhaust systems, heat exchangers, and petrochemical plants. Grade 8C nuts are frequently paired with ASTM A193/A193M stainless steel stud bolts in refinery and thermal processing equipment. ASTM A320/A320M, ASTM A563M, and ASTM F2437/F2437M specifications are also relevant for temperature-sensitive and engineered fastening assemblies.

    ASTM A194/A194M Gr 8C Chemical Requirements

    Grade Description
    and
    UNS Designation    		 C Mn P SE Si Cr Ni CbH
    ASTM A194/A194M Grade 8C (347) S34700 0.08 2.00 0.045 0.030 1.00 17.0-19.0 9.0-12.0 10 x C content, min 1.10
    • (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 Gr 8C Hardness Requirements

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

    ASTM A194/A194M Gr 8C Proof Load Requirements (Inch Series)

    Nominal Size, in. Threads per Inch Stress Area in. 2 Proof Load, lbf A
    Grade 8C
    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 Gr 8C Proof Load Requirements (Metric Series)

    Nominal Size, mm Threads Pitch Stress Area mm 2 Proof Load, kNA
    Grade 8C
    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 A194 Grades & References

    Grade 8C is niobium-stabilised Type 347 austenitic stainless (UNS S34700), preferred for intergranular-corrosion-resistant high-temperature service. The Class 1A variant is Grade 8CA. Titanium-stabilised alternative: Grade 8T (321). Standard 304 service: Grade 8; 316 service: Grade 8M. Dimensions: ASME B18.2.2 heavy hex. Full specification: ASTM A194 PDF. A194 hub.

    International Equivalents

    StandardRegionNotes
    ASTM F593 Group 1 alloy 347USA347 stainless fastener (general)
    ASTM A194-8CA (Class 1A variant)USAClass 1A finished condition
    BS EN 10088-3 1.4550EUNiobium-stabilised austenitic 347
    DIN X6CrNiNb18-10GermanyMaterial number 1.4550 (347)
    ISO 3506-2 A2-NISONb-stabilised austenitic property class
    JIS SUS347JapanType 347 niobium-stabilised austenitic
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