This specification covers the standard requirements for low-carbon age-hardened nickel-copper-chromium-molybdenum-columbium alloy steel forgings for pressure vessel components. Materials shall be manufactured to a killed fine austenitic grain size, by vacuum degas melting process. Heat treatment shall be conducted, according to class, by: normalizing and precipitation hardening (Grade A, Class 1); liquid quenching and precipitation hardening (Grade A, Class 2); or double liquid-quenching, tempering, double austenitizing, and precipitation hardening (Grade B). Heat and product analyses shall be used to evaluate the conformance of forgings to required chemical compositions. Tensile, notch toughness, and Charpy impact requirements shall be examined, for which one of four sampling methods may be employed. One tension test and one impact test (for three samples) shall be made for each forging. Dimensions and finishes of the forgings shall conform to that specified by the purchaser. Repair welding shall also be performed only if permitted by the purchaser.

1.1 This specification covers requirements for low-carbon age-hardening nickel-copper-chromium-molybdenum-columbium alloy steel forgings for pressure vessel components.

1.2 Forgings under this specification are available as Grades A or B. Grade A may be ordered in one or two classes as follows:

1.2.1 Grade A Class 1—Normalized-and-precipitation-heat-treated, providing a minimum yield strength of 55 ksi [380 MPa] and a minimum tensile strength of 65 ksi [450 MPa].

1.2.2 Grade A Class 2—Quenched-and-precipitation-heat-treated, providing a minimum yield strength of 65 ksi [450 MPa] and a minimum tensile strength of 75 ksi [515 MPa].

1.2.3 Grade A was the original steel composition in this specification.

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

1.4 Supplementary requirements, including those applicable in Specification A788/A788M, are provided for use when additional testing or inspection is desired. These shall apply only when specified individually by the purchaser in the order.

1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other and values from the two systems shall not be combined.

1.6 This specification is expressed in both inch-pound and SI units. However, unless the order specifies the applicable “M” specification designation [SI units], the material shall be furnished to inch-pound units.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.