1.1 This specification2 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 6 and Table 1), differing tensile requirements (Section 9 and Table 2), and differing crush and mechanical testing requirements (Sections 10 and 11).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.