"These rules are intended to cover the design and construction of large@ welded@ low-pressure@ carbon steel. above-ground storage tanks that have a single vertical axis of revolution and shall not be considered to include any tank in which the walls are of such a shape that they cannot be generated in their entirety by the rotation of a suitable contour about a single vertical axis of revolution. The tanks are operated at metal temperatures not greater than 200 F and with pressures in their gas or vapor spaces exceeding those permissible under API Standard 650@ Welded Steel Tanks for Oil Storage@ but not exceeding 15 pounds per square inch gage. The basic rules provide for installations in areas where the lowest recorded one-day mean atmospheric temperature is as low as -50 F. Appendix R covers low-pressure storage tanks for refrigerated products from +40 F to -60 F. Appendix Q covers low-pressure storage tanks for liquefied hydrocarbon gases to temperatures not lower than - 270 F. These rules may be used for tanks intended either for holding or storing liquids with gases or vapors above the surface of the liquid or for holding or storing gases or vapors alone. These rules do not apply to ""lift-type"" gas holders. Although these rules do not cover horizontal tanks@ they are not intended to preclude the application of appropriate portions to the design and construction of horizontal tanks designed in accordance with good engineering practice. The details for horizontal tanks not covered by these rules shall be no less safe than the design and construction provided in this standard for . tanks of the shapes expressly covered"