1.1 This specification 2 covers minimum-wall-thickness, electric-resistance-welded tubes made of carbon steel and carbon-manganese steel intended for use as boiler tubes, boiler flues, superheater flues, and safe ends. 1.2 This specification covers Grades A, C, and D with differing chemical requirements (Section 7 and Table 1 ), differing tensile requirements (Section 8 and Table 2 ), and differing mechanical testing requirements (Section 8 ). Note 1: Grades C and D tubes are not suitable for safe-ending for forge welding. 1.3 The tubing sizes and thicknesses usually furnished to this specification are 1 / 2 to 5 in. [12.7 to 127 mm] in outside diameter and 0.035 to 0.360 in. [0.9 to 9.1 mm], inclusive, in minimum wall thickness. Tubing having other dimensions may be furnished, provided such tubes comply with all other requirements of this specification. 1.4 Mechanical property requirements do not apply to tubing smaller than 1 / 8 in. [3.2 mm] in inside diameter or 0.015 in. [0.4 mm] in thickness. 1.5 Optional supplementary requirements are provided and when desired, shall be so stated in the order. 1.6 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. 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.