This guide covers standard specifications for minimum-wall-thickness, seamless carbon steel boiler and superheater tubes for high-pressure service. The steel shall conform to the required chemical composition for carbon, manganese, phosphorus, sulfur, and silicon. The tubes shall have a hardness number not exceeding a specific value. The following mechanical tests shall be conducted, namely: flattening test; flaring test; hardness test; and hydrostatic test.

1.1 This specification² covers minimum-wall-thickness, seamless carbon steel boiler and superheater tubes for high-pressure service.

1.2 The tubing sizes and thicknesses usually furnished to this specification are ¹/₂ in. to 7 in. [12.7 to 177.8 mm] outside diameter and 0.085 to 1.000 in. [2.2 to 25.4 mm], inclusive, in minimum wall thickness. Tubing having other dimensions may be furnished, provided such tubes comply with all other requirements of this specification.

1.3 Mechanical property requirements do not apply to tubing smaller than ¹/₈  in. [3.2 mm] inside diameter or 0.015 in. [0.4 mm] thickness.

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 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. The inch-pound units shall apply unless the “M” designation of this specification is specified in the order.