(A) Materials. Tanks shall be built of steel or concrete unless character of liquid stored requires other materials. Steel commonly known as “mill seconds” shall not be used. Tanks built of materials other than steel shall be designated to specifications embodying safety factors equivalent to those specified in this section for steel tanks. Concrete tanks shall be built in accordance with sound engineering practice. Unlined concrete tanks shall only be used for storage of liquids having a gravity of 40° A.P.I. or heavier. Concrete tanks with special linings may be used for other services provided the design is approved by the Bureau of Fire Prevention. Steel tanks shall be built in accordance with the requirements of divisions (B) through (E) of this section. All shop-built tanks shall be tested at a pressure of not less than five and not more than 10 pounds per square inch (measured at the top of the tank) for a period of at least 10 minutes without leakage or permanent deformation.
(B) Field erected vertical tanks. Vertical tanks erected in the field shall be built in accordance with the following specifications:
(1) A.P.I. Standard No. 12A, September, 1951, Specification for Oil Storage Tanks with Riveted Shells;
(2) A.P.I. Standard No. 12C, September, 1955, Specification for Welded Oil Storage Tanks;
(3) A.P.I. Standard No. 12B, September, 1955, Specification for Bolted Production Tanks;
(4) A.P.I. Standard No. 12D, August, 1955, Specification for Large Welded Production Tanks;
(5) A.P.I. Standard No. 12F, August, 1955, Specification for Small Welded Production Tanks.
(C) Small, shop-built vertical tanks. Vertical tanks not over 1,100 gallons capacity shall meet the following requirements.
Capacity Minimum Thickness of Steel
(in gallons) U.S. Standard
1 to 60 18 gauge
61 to 350 16 gauge
351 to 560 14 gauge
561 to 1,100 12 gauge
(D) Large, shop-built vertical tanks. Vertical tanks over 1,100 gallons capacity shall meet the following requirements:
(1) For tanks up to 25 feet in height the shell shall be not less than three-sixteenths of an inch thick. For tanks from 25 to 30 feet high the bottom ring shall be not less than one-quarter of an inch thick and the remainder of the shell not less than three-sixteenths of an inch thick. For tanks between 30 and 35 feet high, the first two rings shall be not less than one-quarter of an inch thick and the remainder of the shell not less than three-sixteenths of an inch thick. All one-quarter of an inch thick rings shall be not less than five feet wide.
(2) The tops of tanks shall be either dished or cone-shaped and of not less than No. 10 U.S. standard gauge steel.
(3) Tanks shall be welded, or riveted and caulked, or otherwise made tight in a workmanlike manner. The roof of the tank shall be securely fastened to the top ring of the shell with a joint having the same tightness as the joints between rings. The joint between roof and shell shall be weaker than any other joints in the shell of the tank. Joints in the roof shall be welded or riveted or made tight by other process satisfactory to the Chief of the Bureau of Fire Prevention. Roofs of tanks shall have no unprotected openings.
(E) Shop-built horizontal tanks. Horizontal tanks shall be constructed in accordance with accepted engineering practice and shall meet the following minimum requirements: joints shall be riveted and caulked, riveted and welded, or welded. Tanks heads over six feet in diameter shall be dished, stayed, braced, or reinforced.
(1) Small, shop-built horizontal tanks. Horizontal tanks not over 1,100 gallons capacity shall meet the following requirements:
Capacity Minimum Thickness of Steel
(in gallons) U.S. Standard
1 to 60 18 gauge
61 to 275 14 gauge
276 to 550 12 gauge
551 to 1100 10 gauge
(2) Large, shop-built horizontal tanks. Horizontal tanks over 1,100 gallons capacity having a diameter of not over six feet, made of steel, shall be three-sixteenths of an inch or greater nominal thickness. Tanks having a diameter of over six feet and not more than 12 feet, made of steel, shall be one quarter of an inch or greater nominal thickness.
('81 Code, § 5.40.180) Penalty, see Ch. 13