This specification covers the 8 and 9% nickel-alloy steel forged or rolled flanges, fittings, valves, and parts intended for use in welded pressure vessels for low-temperature service. Two types of materials are specified according to the chemical composition: type I and type II. Materials for forgings shall consist of ingots, or either forged or rolled blooms, billets, or bars. Except for all types of flanges, elbows, return bends, tees, and header tees, other parts including NPS 4 may be machined from hot-rolled or forged bar. The steel shall conform to the specified chemical requirements for carbon, manganese, phosphorus, sulfur, silicon, and nickel. The following methods of heat treatment shall be used: quenched and tempered and double normalized and tempered. Two tests shall be done to meet the mechanical requirements of the material: tension test and Charpy impact test.

1.1 This specification² covers 8 and 9 % nickel-alloy steel forged or rolled flanges, fittings, valves, and parts intended for use in welded pressure vessels for low-temperature service. The specification is applicable to forgings with maximum section thickness of 3 in. [75 mm] in the double normalized and tempered condition and 5 in. [125 mm] in the quenched and tempered condition. Forgings under this specification are intended for service at operating temperatures not lower than −320 °F [−196 °C] for Type I or −275 °F [−170 °C] for Type II or higher than 250 °F [121 °C].

1.2 Material under this specification is available in two types having different chemical compositions as follows:

Type

Nominal Nickel Content, %

I
II

9
8

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

1.4 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 may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.