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    2. Grade 2 Nuts

    ASTM A194 Grade 2 Heavy Hex Nuts — UNS K04100

    Medium carbon steel nuts suitable for pressure vessel and high-temperature bolting systems.

    ASTM A194/A194M Grade 2 Nuts are medium carbon steel heavy hex nuts engineered for elevated strength and reliable performance in industrial bolting systems. These nuts are commonly selected for high-pressure flanges, piping assemblies, and refinery equipment. They are extensively used with ASTM A193/A193M stud bolts and compatible fastening systems across oil & gas, power generation, and chemical processing industries. ASTM A320/A320M bolting combinations are also used for controlled temperature environments, while ASTM A563M and ASTM F2437/F2437M standards support additional structural and engineered fastening applications.

    ASTM A194/A194M Grade 2 Chemical Requirements

    Grade Description
    and
    UNS Designation    		 C Mn P SE Si
    ASTM A194/A194M Grade 2 C 0.40 min 1.00 0.040 0.050 0.40
    • (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 Grade 2 Hardness Requirements

    Grade and Type Completed Nuts Sample Nut after Treatment
    Brinell Hardness Rockwell Hardness Brinell Hardness, min Rockwell Hardness B Scale, min
    B Scale
    ASTM A194/A194M Grade 2 159 to 352 84 min 159 84

    ASTM A194/A194M Grade 2 Proof Load Requirements (Inch Series)

    Nominal Size, in. Threads per Inch Stress Area in. 2 Proof Load, lbf A
    Grade 2
    Heavy HexD HexE
    1/4 20 0.0316 4 770 4 300
    5/16 18 0.0524 7 860 7 070
    3/8 16 0.0774 11 620 10 460
    7/16 14 0.1063 15 940 14 350
    1/2 13 0.1419 21 280 19 160
    9/16 12 0.182 27 300 24 570
    5/8 11 0.226 33 900 30 510
    3/4 10 0.334 50 100 45 090
    7/8 9 0.462 69 300 62 370
    1 8 0.606 90 900 81 810
    11/8 8 0.790 118 500 106 700
    11/4 8 1.000 150 000 135 000
    13/8 8 1.233 185 000 166 500
    11/2 8 1.492 223 800 201 400
    • (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 Grade 2 Proof Load Requirements (Metric Series)

    Nominal Size, mm Threads Pitch Stress Area mm 2 Proof Load, kNA
    Grade 2
    Heavy HexD HexE
    M6 1.0 20.1 20.8 18.7
    M8 1.25 36.6 37.9 34.0
    M10 1.50 58.0 60.0 53.9
    M12 1.75 84.3 87.3 78.4
    M14 2.0 115.0 119.0 107.0
    M16 2.0 157.0 162.5 146.0
    M20 2.5 245.0 253.6 227.8
    M22 2.5 303.0 313.6 281.8
    M24 3.0 353.0 365.4 328.3
    M27 3.0 459.0 475.1 426.9
    M30 3.5 561.0 580.6 521.7
    M36 4.0 817.0 845.6 759.8
    • (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 2 is a quenched-and-tempered medium-carbon-steel A194 nut. The most-used variant is Grade 2H (heavy hex refinery standard). Sour-service equivalent: Grade 2HM. For stainless service: Grade 8 (304), Grade 8M (316). Dimensions: ASME B18.2.2 heavy hex. Full specification: ASTM A194 PDF. A194 hub.

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