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Subchapter 1. Unfired Pressure Vessel Safety Orders
Article 7. Compressed and Liquefied Natural Gas System

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§532. Installation of Aboveground Storage Tanks.

(a) General.

(1) Storage tanks installed aboveground shall be installed on firm masonry or concrete foundations. Aboveground horizontal tanks shall have no more than 2 points of support longitudinally. Where necessary, tanks shall be securely anchored to prevent floating.

(2) Metallic structural supports, when used, shall be encased in concrete or other material having a fire resistant rating of at least 2 hours when the distance between the lower surface of the tank and the top of the concrete or masonry foundations exceeds 18 inches. In the case of a vertical tank having no more than one opening in the support skirt, interior fire protection of the skirt may be omitted. (Tanks of not more than 575-gallon capacity installed in areas having an average snowfall exceeding 18 inches may, at the discretion of the Division, be exempt from the provisions of this paragraph.)

(3) Every tank shall be so supported as to prevent the concentration of excessive loads on the tank at the points of support. All foundations and fastenings shall be designed to provide reasonable safety under all imposed loads including wind, earthquake, vibrations, etc. All tanks over 1,200 gallons capacity shall be installed on foundations in such a manner as to permit expansion and contraction.

(4) The valves and other appurtenances on tanks at all bulk plants, if the plant is not otherwise fenced, shall be surrounded by a rugged steel fence or equivalent. Fences which are not of an open mesh type may be used providing they are acceptable to both the local fire department and the Division. The fence required by this Section shall be at least 6 feet in height. Any fence completely surrounding the tank shall be located a minimum distance of 3 feet from the tank. Other tanks shall also be surrounded by a rugged steel fence or equivalent, if in the opinion of the Division a fence is needed to prevent unauthorized tampering. All fenced areas shall be kept locked when unattended.

(5) Aboveground storage tanks shall be protected from impact from trucks, trailers and other vehicles, where such impact is likely or probable, by suitable curbs, fences or posts and railings. Such curbs or fences shall arranged so that they will not hamper free ventilation around the tanks.

(6) All loading and unloading connections at bulk plants shall be secured to a concrete bulkhead or equivalent designed to withstand the load imposed by the strongest pipe, hose or flexible metal hose, and fittings to be used in the transfer operation without breaking, or 2,000 pounds whichever is greater unless other adequate protection is provided. This bulkhead shall not be located underneath the tank. The loading and unloading connections shall be firmly secured to this bulkhead and the line between the bulkhead and tank shall be installed in a manner to provide for expansion, contraction, jarring, vibration and settling. Such bulkhead shall be located no less than 25 feet from the nearest important building or line of property adjoining that may be built upon. When in the opinion of the Division such bulkhead is necessary for the safety of the place of employment, it shall be required at storage plants other than bulk plants mentioned above.

(7) The fill line on storage tanks shall be equipped with a back-flow check valve to prevent discharge of the natural gas from the receiving tank in case of line, hose or fittings rupture.

(8) A fire extinguisher conforming to the provisions of California Administrative Code, Title 19, Chapter 1, Subchapter 3, and having a rating of not less than 20B shall be available and ready for use during the time natural gas is being transferred. The extinguisher carried on a bulk delivery or transportation vehicle may be considered as meeting the requirements of this Order when transferring natural gas from or to such vehicle provided the extinguisher has the required rating list above.

(b) Compressed Natural Gas.

(1) When the tank is installed directly on concrete or masonry foundations, a corrosion pad shall be provided at the points of contact with the foundation. These corrosion pads shall be at least 3/16-inch thick, and have a width at least equal to the width of the foundation at the point of contact with the tank, but in no case shall they be less than 8 times the shell thickness in width. When corrosion pads or pad-type steel supports are used, the pads shall have corners rounded to a radius of not less than 6 times the pad thickness, and shall be attached to the shell with a continuous seal weld. These pads shall be not less than 1/4 the circumference of the shell in length.

(2) Pressure vessels which are made of materials that are subject to corrosion by atmospheric conditions and which are not provided with an allowance for external corrosion by a suitable increase in the design thickness shall be protected by painting or other equivalent means necessary to check active corrosion.

(3) Cylinders used at dispensing stations shall be installed on firm concrete or masonry foundations and located in accordance with 531(a) and (b).

(c) Liquefied Natural Gas.

(1) Supports for LNG tanks shall be designed to withstand low temperature effects of LNG spillage.

(2) LNG tanks installed in battery shall be so installed that the 90 percent outage levels or the top surfaces of the tanks are substantially in the same horizontal plane.

(3) Tanks installed in battery shall not be installed with liquid and/or vapor lines connecting into common headers unless either:

(A) The working pressure of all such tanks is the same.

(B) Check valves or other devices are installed in the system to prohibit the introduction of the higher pressure product into the lower pressure tank.


1. Amendment of subsection (b) filed 8-7-76; effective thirtieth day thereafter (Register 76, No. 32).

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