1.1 ?This specification2 covers heavy-wall carbon and alloy steel pipe (Note 1 ) made from turned and bored forgings and is intended for high-temperature service. Pipe ordered under this specification shall be suitable for bending and other forming operations and for fusion welding. Selection will depend on design, service conditions, mechanical properties and high-temperature characteristics. Note 1: ?The use of the word “pipe” throughout the several sections of this specification is used in the broad sense and intended to mean pipe headers, or leads. Note 2: ?The dimensionless designator NPS (nominal pipe size) has been substituted in this standard for such traditional terms as “nominal diameter,” “size,” and “nominal size.” 1.2 ?Several grades of ferritic steels are covered. Their compositions are given in Table 1 . 1.3 ?Supplementary requirements (S1 to S7) of an optional nature are provided. Supplementary requirements S1 to S5 call for additional tests to be made, and when desired shall be so stated in the order, together with the number of such tests required as applicable. 1.4 ?The values stated in either SI units or inch-pound 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. The inch-pound units shall apply unless the “M” designation of this specification is specified in the order. 1.5 ?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.