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    2. ASTM A193/A193M Grade B8MA Class 1A

    ASTM A193/A193M Grade B8MA Class 1A Stud Bolts – UNS S31600

    Strain hardened, molybdenum-bearing 316 stainless steel stud bolts providing superior corrosion resistance and higher mechanical strength for demanding applications.

    ASTM A193/A193M Grade B8MA Class 1A Stud Bolts are manufactured from UNS S31600 Type 316 molybdenum-bearing austenitic stainless steel and cold worked to achieve the elevated tensile and yield strength requirements of the Class 1A designation, with mechanical property verification conducted on the finished fastener as stipulated by ASTM A193. The molybdenum content, typically 2–3%, enhances pitting corrosion resistance in chloride environments beyond what standard 304-type grades can offer, and the strain hardening process substantially increases the load-carrying capacity of the bolt. This combination makes Grade B8MA Class 1A stud bolts one of the most commonly specified grades for high-pressure, high-temperature flanged joints in offshore platforms, chemical reactors, desalination systems, and marine installations where both the mechanical demands of pressurized service and the chemical aggressiveness of the operating environment must be simultaneously addressed by the fastening system.

    ASTM A193/A193M Grade B8MA Class 1A Chemical Composition - Austenitic Steels

    Grade Description and UNS Designatio Classes C Mn P S Si Cr Ni Mo
    ASTM A193 Grade B8MA 316, S31600 1, 1A, 1D, 2 0.08 2.00 0.045 0.030 1.00 16.0-18.0 10.0-14.0 2.00-3.00
    Product Analysis VariationB 0.01 0.04 0.010 0.005 0.05 0.20 0.15 0.10
    • (A) Values are maximums unless a range or a minimum is indicated. Where ellipses appear in this table, there is no requirement and the element need not be determined or reported. The intentional addition of Bi, Se, Te, and Pb is not permitted.
    • (B) Product Analysis-Individual determinations sometimes vary from the specified limits as shown in the tables. The several determinations of any individual element in a heat may not vary both above and below the specified range. Product variation limits are over for maximums, over or under for ranges, and under for minimums, unless otherwise indicated.
    • (C) Typical steel compositions used for this grade include 4140, 4142, 4145, 4140H, 4142H, and 4145H.
    • (D) For bar sizes over 31/2 in. [90 mm], inclusive, the carbon content may be 0.50% max. For the B7M grade, a minimum carbon of 0.28% is permitted, provided that the required tensile properties are met in the section sizes involved, the use of AISI 4130 or 4130H is allowed.
    • (E) Total of soluble and insoluble.
    • (F) Columbium and Niobium are alternate names for element 41 in the Periodic Table of the Elements.

    ASTM A193/A193M Grade B8MA Class 1A Mechanical Requirements - Austenitic Steels (Inch)

    Grade Diameter,
    in.     		Heat TreatmentB Tensile Strength,
    min, ksi     		Yield Strength, min,
    0.2 % offset, ks     		Elongation in 4 D,min Reduction of Area, min Hardness,
    max
    ASTM A193 Grade B8MA Class 1A All diameters carbide solution treated in the finished condition 75 30 30 50 192 HBW or 90 HRB
    • (A) To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
    • (B) Class 1 is solution treated. Class 1A is solution treated in the finished condition for corrosion resistance; heat treatment is critical due to physical property requirement. Class 2 is solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over 3/4 in. in diameter.
    • (C) For sizes3/4 in. in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.
    • (D) For diameters 11/2 and over, center (core) properties may be lower than indicated by test reports which are based on values determined at1/2 radius.

    ASTM A193/A193M Grade B8MA Class 1A Mechanical Requirements - Austenitic Steels (Metric)

    Grade Class ,
    mm     		Diameter Heat TreatmentB Tensile Strength,
    min,MPa     		Yield Strength, min,
    0.2 % offset, MPa     		Elongation in 4 D,min % Reduction of Area, min % Hardness,
    max
    ASTM A193 Grade B8MA Class 1A All diameters carbide solution treated in the finished condition 515 205 30 50 192 HBW or 90 HRB
    • (A) To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
    • (B) Class 1 is solution treated. Class 1A is solution treated in the finished condition for corrosion resistance; heat treatment is critical due to physical property requirement. Class 2 is solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over M20 mm in diameter.
    • (C) For sizes M20 mm in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.
    • (D) For diameters M38 and over, center (core) properties may be lower than indicated by test reports which are based on values determined at1/2 radius.

    ASTM A193/A193M Grade B8MA Class 1A Bolting Components Marking - Austenitic Steels

    Grade Class Grade Symbol
    ASTM A193 Grade B8MA Class 1A TB B8D or TB B8MA
    TB B8V or TB B8MA

    Related ASTM A193 Grades & ASME Companion Dimensions

    Frequently Asked Questions

    What is ASTM A193 Grade B8MA Class 1A?
    ASTM A193 Grade B8MA Class 1A is a bolting material covering 316 SS Mo-bearing for chloride/sour (UNS S31600). Class 1A — solution treated in finished condition for corrosion resistance. Used in high-temperature, high-pressure flange, pressure-vessel and heat-exchanger bolting service per ASTM A193/A193M.
    What is the UNS designation for ASTM A193 Grade B8MA Class 1A?
    The UNS designation for ASTM A193 Grade B8MA Class 1A is UNS S31600. This corresponds to 316 SS Mo-bearing for chloride/sour. The UNS code is universal across ASTM, ASME (SA-193), PED 2014/68/EU and NORSOK material specifications. The 'Class 1A' designator denotes the heat treatment condition under ASTM A193 Table 3.
    Why is ASTM A193 Grade B8MAA preferred over B8 (Class 1A)?
    Grade B8MAA (316 SS with 2–3% Mo) provides significantly improved pitting and crevice corrosion resistance vs B8 (304 SS) in chloride, sour-service and marine environments. PREN ≈ 24 for 316 vs ≈ 19 for 304. Specific to ASTM A193 Grade B8MA Class 1A: Class 1A — solution treated in finished condition for corrosion resistance.
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