scope:

These rules are intended to cover the design and construction of large, welded, low-pressure, carbon steel, aboveground storage tanks which have a single vertical axis of revolution and 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 (formerly API Standard 12C), but not exceeding 15 psig. Provision is made 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.

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, but do not apply to "lift-type" gas holders. Although these rules are not intended to cover horizontal tanks, they are not intended to preclude the application of appropriate portions hereof to the design and construction of horizontal tanks designed in accordance with good engineering practice, in which the details not covered by these rules are no less safe than the design and construction provided herein for tanks of the shapes expressly covered.