This specification covers the standard for low-carbon manganese-molybdenum-columbium alloy steel plates for piping components and welded pressure vessels. Different alloy steel classes are covered such as Class 1, 2, 3, and 4. The steel shall be killed and shall conform to the fine austenitic grain size requirement. As-rolled plates shall undergo precipitation heat treatment, quenching, or tempering. Heat and product analyses shall be performed on the steel and shall conform to the prescribed chemical composition in carbon, manganese, phosphorus, sulfur, silicon, columbium, molybdenum, and copper. Tensile test and notch-toughness test shall be done on the material and shall conform to the required yield strength, tensile strength, and elongation.

1.1 This specification covers low-carbon manganese-molybdenum-columbium alloy steel plates for piping components and welded pressure vessels.

1.2 Four different classes are covered, which provide various tensile strength properties. A Charpy V-notch energy absorption requirement of 20 ft·lbf [27J] at −50°F [−45°C] is specified for all grades.

1.2.1 Classes 1 and 2 provide minimum yield strength levels of 65 ksi [450 MPa] and 70 ksi [485 MPa] respectively. Both classes can be provided in the as-rolled condition or in the quenched-and-tempered condition.

1.2.2 Class 3 provides a minimum yield strength level of 75 ksi [515 MPa]. This grade can be provided in the as-rolled and precipitation heat-treated condition or in the quenched-and-tempered condition.

1.2.3 Class 4 provides a yield strength level of 80 ksi [550 MPa] in the as-rolled and precipitation heat-treated condition.

1.3 Current practice limits plate thickness furnished under this specification. The individual manufacturer should be consulted on size and thickness limitations.

1.4 Welding procedures are of fundamental importance and must be such as not to adversely affect the properties of the material, especially in the heat-affected zone. It is presupposed that welding procedures will be suitable for the materials being welded.

1.5 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.