Sets out requirements for seamless and electric resistance-welded tubes of carbon and alloy steels and for cold finished seamless tubes of austenitic steels, not exceeding 1/2 inch thick and 5 inch outside diameter, for use in the construction of boiler units. Tubes manufactured in accordance with this specification have specified proof stress properties at elevated temperatures. Data on the long term elevated temperature properties 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.