1305.14.2 Additional Construction Standards for Cylindrical Tanks Exceeding 275 Gallons (1041 L)

Cylindrical tanks, including oval, elongated oval, or round tanks, exceeding 275 gallons (1041 L) shall comply with the requirements of Sections 1305.14.2.1 through 1305.14.2.3.

Exception: Such above-ground vertical tanks that are outside of buildings shall comply with Sections 1305.14.1 and 1305.14.5.

The minimum thickness shall be as follows:

1. Tanks 36 inches (914 mm) in diameter or less shall have at least a ¹/₄-inch (6.4 mm) shell and ¹/₄-inch (6.4 mm) heads.
2. Tanks 37 inches (940 mm) to 72 inches (1829 mm) in diameter shall have at least a ¹/₄-inch (6.4 mm) shell and ⁵/₁₆-inch (7.9 mm) heads.
3. Tanks 73 inches (1854 mm) to 120 inches (3048 mm) in diameter shall have at least a ⁵/₁₆-inch (7.9 mm) shell and ³/₈-inch (9.5 mm) heads.
4. Tanks over 120 inches (3048 mm) in diameter shall be of at least ³/₈-inch (9.5 mm) steel and shall be stiffened by angle rings or equivalent members so as to retain their cylindrical form.

Dished heads for such tanks shall have a curvature the radius of which is not greater than the diameter of the tank. Dished heads shall be formed with an adequate cylindrical extension rim to provide a welding surface.

If flat heads are used, they shall be braced in the same manner as described for the bracing of flat sides of rectangular tanks as provided for in Section 1305.14.3.