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    2. Grade 2HM Nuts

    ASTM A194 Grade 2HM Heavy Hex Nuts — UNS K04100

    High-strength quenched and tempered nuts for demanding temperature and pressure conditions.

    ASTM A194/A194M Grade 2HM Nuts are heat-treated heavy hex nuts manufactured for enhanced mechanical properties and elevated temperature resistance. These nuts are widely used in boilers, pressure vessels, heat exchangers, and refinery piping systems. Grade 2HM nuts are regularly paired with ASTM A193/A193M B7 and B16 stud bolts in critical industrial assemblies. They also support ASTM A320/A320M low-temperature bolting applications and are integrated into projects requiring ASTM A563M and ASTM F2437/F2437M compliant fastening systems.

    ASTM A194/A194M Grade 2HM Chemical Requirements

    Grade Description
    and
    UNS Designation    		 C Mn P SE Si
    ASTM A194/A194M 2HM 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 2HM 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 2HM 159 to 235 84 to 99 159 84

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

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

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

    Grade 2HM is the sour-service variant of Grade 2H, hardness-controlled to 22 HRC max per NACE MR0175 / ISO 15156 for H2S-bearing environments. For standard non-sour service, use Grade 2H. The Cr-Mo sour-service equivalent is Grade 7M (matched to A193 B7M studs). For stainless sour service consider Grade 8M (316) or Grade 8MN (316N). Dimensional standards: ASME B18.2.2 heavy hex. Reference: ASTM A194 PDF · A194 hub.

    International Equivalents (Sour-Service)

    StandardRegionNotes
    ASTM A194-2HUSANon-sour-service base grade
    API 20E BSL-1APISour-service bolting specification
    NACE MR0175 / ISO 15156GlobalSour-service materials requirement
    BS EN 10269EUSour-service bolting standard
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