1.1 This specification covers carbon and alloy steel pipe, electric-fusion-welded with filler metal added, fabricated from pressure-vessel-quality plate of several analyses and strength levels and suitable for high-pressure service at high temperatures. Heat treatment may or may not be required to attain the desired mechanical properties or to comply with applicable code requirements. Supplementary requirements are provided for use when additional testing or examination is desired. 1.2 The specification nominally covers pipe 16 in. (405 mm) in outside diameter and larger with wall thicknesses up to 3 in. (75 mm) inclusive. Pipe having other dimensions may be furnished provided it complies with all other requirements of this specification. 1.3 Several grades and classes of pipe are provided. 1.3.1 Grade designates the type of plate used as listed in Table 1. 1.3.2 Class designates the type of heat treatment performed in the manufacture of the pipe, whether the weld is radiographically examined, and whether the pipe has been pressure tested as listed in 1.3.3. 1.3.3 Class designations are as follows (Note 1): Note 1 -Selection of materials should be made with attention to temperature of service. For such guidance, Specification A 20/A 20M may be consulted. 1.4 Optional requirements of a supplementary nature are provided, calling for additional tests and control of repair welding, when desired. 1.5 The values stated in inch-pound units are to be regarded as the standard.