Sets out requirements for seamless and electric resistance-welded carbon steel tubes, not exceeding 5 inch outside diameter, intended primarily for boilers and unfired pressure vessels for use at temperatures not in excess of 400 degrees Celsius (725 degrees F). Data on the mechanical properties at elevated temperatures for the materials specified is given in Appendix C. This data may be used for design purposes in accordance with the application code but is not subject to verification. Diameters and thicknesses of tubes appropriate to this specification are shown in Appendix D.