This specification covers manganese-molybdenum and manganese-molybdenum-nickel alloy steel plates for use in welded pressure vessels. The steel materials shall be killed and shall conform to the required values of fine austenitic grain and shall also be heat treated. The steel specimens shall undergo heat analysis and product analysis and shall conform to the chemical requirements for carbon, manganese, phosphorus, sulfur, silicon, molybdenum, and nickel. Tension tests shall be performed wherein the steel specimens shall conform to the required values of tensile strength, yield strength, and elongation.

1.1 This specification covers one type of manganese-molybdenum and four types of manganese-molybdenum-nickel alloy steel plates for use in the quenched and tempered condition for the construction of welded pressure vessels.

1.2 Material under this specification is available in five types, designated “A”, “B”, “C”, “D”, and “E”. The material is also available in three classes having the following strength levels.

1.3 The maximum thickness of Class 1 and Class 2 plates is limited only by the capacity of the composition to meet the specified mechanical property requirements; however, current practice normally limits the maximum thickness to 12 in. [300 mm] for Types A through D. Current practice limits the maximum thickness for Type E to 6 in. [150 mm] for Class 1 and 3¹/₄ in. [80 mm] for Class 2.

1.4 The maximum thickness of Class 3 plates is 2½ in. [65 mm] for Types A through D and 2 in. [50 mm] for Type E.

1.5 The minimum nominal thickness of plates of all classes is 0.25 in. [6.5 mm].

1.6 These alloy steel plates in the as-rolled condition are sensitive to cracking during transit and handling, particularly in thicknesses over about 1 or 2 in. [25 or 50 mm]. They should be shipped in the as-rolled conditions only by mutual agreement of manufacturer and the purchaser.

1.7 Plates covered by this specification are often used in the beltline region of nuclear reactor vessels where the material properties may be affected by high levels of radiation. Appendix X1 provides some information pertinent to this usage.

1.8 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.