105.20-3—Cargo tanks.
(a) Construction and Materials.
(1)
The cargo tanks must be constructed of iron, steel, copper, nickel alloy, copper alloy; or aluminum. The tanks shall be designed to withstand the maximum head to which they may be subjected, except that in no case shall the thickness of the shell or head be less than that specified in this subparagraph. Tanks of over 150 gallons capacity shall have a minimum thickness as indicated in Table 105.20-3(a)(1):
| Material | A.S.T.M. specification (latest edition) | Thickness in inches and gage number 2,3 |
|---|---|---|
| Nickel copper | B127, hot rolled sheet or plate | 0.107 (USSG 12). |
| Copper nickel 1 | B122, Alloy No. 5 | 0.128 (AWG 8). |
| Copper 1 | B152, Type ETP | 0.182 (AWG 5). |
| Copper silicon 1 | B97, Alloys A, B, and C | 0.144 (AWG 7). |
| Steel or iron | 0.179 (MSG 7). | |
| Aluminum 4 | B209, Alloy | 5 5086 0.250 (USSG 3). |
| 1 Tanks fabricated with these materials shall not be utilized for the carriage of diesel oil. | ||
| 2 The gage numbers used in this table may be found in many standard engineering reference books. The letters “USSG” stand for “U.S. Standard Gage” which was established by the act of Mar. 3, 1892 ( 15 U.S.C. 206 ) for sheet and plate iron and steel. The letters “AWG” stand for “American Wire Gage” (or Brown and Sharpe Gage) for nonferrous sheet thicknesses. The letters “MSG” stand for “Manufacturers' Standard Gage” for sheet steel thicknesses. | ||
| 3 Tanks over 400 gallons shall be designed with a factor of safety of four on the ultimate strength of the tank material used with a design head of not less than 4 feet of liquid above the top of the tank. | ||
| 4 Anodic to most common metals. Avoid dissimila-metal contact with tank body unless galvanically compatible. | ||
| 5 And other alloys acceptable to the Commandant. | ||
(2)
All tank joints, connections, and fittings shall be welded or brazed. Tanks with flanged-up top edges will not be acceptable.
(3)
All tanks exceeding 30 inches in any horizontal dimension shall be fitted with vertical baffle plates of the same material as the tank. Limber holes at the bottom and air holes at the top of all baffles shall be provided. Tanks constructed of material of greater thickness than minimum requirements and that are reinforced with stiffeners may be accepted without baffles.
(4)
An opening fitted with a threaded pipe plug may be used on the bottom of the tank for cleaning purposes.
(b) Supports.
(1)
Tanks shall be adequately supported and braced to prevent movement. The supports and braces shall be insulated from contact with the tank surface with a nonabrasive and nonabsorbent material.
(c) Fittings.
(1)
Filling lines shall be at least 1 1/2 inches standard pipe size and extend to within 1 1/2 -pipe diameters of the bottom of the tank.
(2)
Suction lines from diesel oil tanks may be taken from the bottom provided a shutoff valve is installed at the tank. Tanks for Grades B and C liquids shall have top suctions only.
(4)
When a cargo tank contains Grades B or C liquids, the vent lines shall be terminated with an approved pressure vacuum relief valve not less than 3 feet above the weather deck. When a cargo tank contains Grades D or E liquids the vent line may be terminated with a gooseneck fitted with flame screen at a reasonable height above the weather deck.
(d) Hydrostatic tests.
All tanks vented to the atmosphere shall be hydrostatically tested to a pressure of 5 pounds per square inch or 1 1/2 times the maximum head to which they may be subjected in service. A standpipe of 11 1/2 feet in length attached to the tanks may be filled with water to accomplish the 5 pounds per square inch test.
[CGFR 69-53, 34 FR 11265, July 4, 1969, as amended by CGD 72-206R, 38 FR 17229, June 29, 1973; CGD 76-061, 41 FR 23401, June 10, 1976]