(1) Gravity type cargo tanks shall be designed and tested to meet the rules of the American Bureau of Shipping for a head of water at least 8 feet above the tank top or the highest level the lading may rise, whichever is the greater. The plate thickness of any part of the tank shall not be less than three-eighths inch.
(2) Gravity tank vents.
(i) The outlet end of the gravity tank vent shall terminate above the weatherdeck, clear of all obstructions and away from any source of ignition.
(ii) The gravity tank vent shall terminate in a gooseneck bend and shall be fitted with a single flame screen or two fitted flame screens as described in § 151.03-25. No shutoff valve or frangible disk shall be fitted in the vent lines.
(1) Pressure vessel type cargo tanks shall be independent of the vessel's structure and shall be designed for the maximum pressure to which they may be subjected when compressed air is used to discharge the cargo, but in no case shall the design pressure be less than that indicated as follows:
Fluorosilicic Acid - 50 pounds per square inch gauge.
Hydrochloric Acid - 50 pounds per square inch gauge.
Hydrofluorosilicic Acid, see Fluorosilicic Acid.
Phosphoric Acid - 30 pounds per square inch gauge.
Sulfuric Acid - 50 pounds per square inch gauge.
(2) Pressure vessel type cargo tanks shall be of welded construction meeting the requirements for Class II or Class III given in Part 54 of this chapter.
(3) When compressed air is used to discharge the cargo, the tank shall be fitted with a vent led to the atmosphere in which a rupture disk shall be installed. The rupture disk shall be designed to burst at a pressure not exceeding the design pressure of the tank. An auxiliary vent to relieve the pressure or vacuum in the tank during the cargo transfer operation may be led from the vent line between the tank and the rupture disk. A shutoff valve may be fitted in the auxiliary vent.
(c) Openings in tanks are prohibited below deck, except for access openings used for inspection and maintenance of tanks, or unless otherwise specifically approved by the Commandant. Openings shall be fitted with bolted cover plates and acid-resistant gaskets.
(d) Where special arrangements are approved by the Commandant to permit a pump suction to be led from the bottom of the tank, the filling and discharge lines shall be fitted with shutoff valves located above the weatherdeck or operable therefrom.
(e) The outage shall not be less than 1 percent.
(f) All enclosed compartments containing cargo tanks and all machinery spaces containing cargo pumps shall be fitted with effective means of ventilation.
(g) A separator shall be fitted in compressed air lines to the tank when air pressure is used to discharge the cargo.
(h) Only installed electric or portable battery lights shall be used during the cargo transfer operations. Smoking is prohibited and the person in charge of cargo transfer shall post No Smoking signs during cargo transfer operations.
(i) Tanks approved for the transportation of acid cargoes subject to this section shall not be used for the transportation of any other commodity, except upon authorization by the Commandant (CG-ENG).
(j) Each cargo tank shall be subjected to an internal examination at least once in every 4 years. If cargo tank lining is required and the lining of the cargo tank has deteriorated in service or is not in place, the Marine Inspector may require the tank to be tested by such nondestructive means as he may consider necessary to determine its condition.
(k) The special requirements for fluorosilicic acid in § 151.50-77, for hydrochloric acid in § 151.50-22, for hydrofluorosilicic acid, see fluorosilicic acid, for phosphoric acid in § 151.50-23, and for sulfuric acid in § 151.50-21 also apply to the carriage of those acids.
[CGFR 70-10, 35 FR 3714, Feb. 25, 1970, as amended by CGD 80-001, 46 FR 63279, Dec. 31, 1981; CGD 82-063b, 48 FR 4781, Feb. 3, 1983; CGD 88-100, 54 FR 40040, Sept. 29, 1989; CGD 92-100, 59 FR 17028, Apr. 11, 1994]