46 C.F.R. § 105.12 – Cargo tank and pumping system requirements.

(a) Cargo tanks for the carriage of bulk flammable or combustible liquids must be constructed of iron, steel, copper, nickel alloy, copper alloy, or aluminum. Tanks must be designed to withstand the maximum head to which they may be subjected, and tanks of more than 150 gallons capacity must have at least the thickness indicated in Table 1 of § 105.12.

Table 1 to § 105.12—Tank Thickness
Material	ASTM specification (latest edition)	Thickness in inches and gauge 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 must not be utilized for the carriage of diesel oil.
2 The gauge numbers used in this table may be found in many standard engineering reference books. The letters “USSG” stand for “U.S. Standard Gauge” which was established by the act of March 3, 1892 (15 U.S.C. 206) for sheet and plate iron and steel. The letters “AWG” stand for “American Wire Gauge” (or Brown and Sharpe Gauge) for nonferrous sheet thicknesses. The letters “MSG” stand for “Manufacturers' Standard Gauge” for sheet steel thicknesses.
3 Tanks of more than 400 gallons capacity must 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 dissimilar-metal contact with tank body unless galvanically compatible.
5 And other alloys acceptable to the Commandant.

(1) All tank joints, connections, and fittings must be welded or brazed, and tanks may not have flanged-up top edges.
(2) A tank exceeding 30 inches in any horizontal dimension must be fitted with vertical baffle plates of the same material as the tank, unless the tank has a greater thickness than minimum requirements and is reinforced with stiffeners. Limber holes at the bottom and air holes at the top of all baffles must be provided.
(3) An opening fitted with a threaded pipe plug may be used on the bottom of the tank for cleaning purposes.

(b) Supports. Tanks must be adequately supported and braced to prevent movement. Supports and braces must be insulated from contact with the tank surface using a nonabrasive and nonabsorbent material.
(c) Fittings.
1. (1) Filling lines must 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. (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 must have top suctions only.
3. (3) Vent lines must be at least equal in size to the filling lines.
4. (4) When a cargo tank contains Grades B or C liquids, the vent lines must 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 a flame screen at a reasonable height above the weather deck.
(d) Hydrostatic tests. Tanks vented to the atmosphere must 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.
(e) Piping systems.
1. (1) Piping must be copper, nickel copper, or copper nickel, with a minimum wall thickness of 0.035 inches; except that seamless steel piping or tubing providing equivalent safety may be used for diesel cargo systems.
2. (2) Valves must be of a suitable nonferrous metallic Union Bonnet type with ground seats, except that steel or nodular iron may be used in cargo systems that use steel pipe or tubing.
3. (3) Aluminum or aluminum alloy valves and fittings may not be used in cargo lines.
(f) Pumps.
1. (1) Pumps for cargo dispensing must be of a type satisfactory for the purpose.
2. (2) A relief valve must be provided on the discharge side of the pump if the pressure under shutoff conditions exceeds 60 pounds. When a relief valve is installed, it must discharge back to the suction of the pump.
3. (3) Where electric motors are installed with dispensing pumps, they must be explosion-proof and so labeled by UL or another recognized laboratory, as suitable for Class I, Group D atmospheres.
(g) Grounding.
1. (1) All tanks and associated lines must be electrically grounded to the vessel's common ground.
2. (2) A grounded type hose and nozzle must be used for dispensing fuels.
(h) Cargo tanks installed below decks—additional requirements.
1. (1) Compartments or areas containing tanks or pumping systems must be closed off from the remainder of the vessel by gastight bulkheads. Such gastight bulkheads may be pierced for a drive shaft and pump engine control rods if the openings are fitted with stuffing boxes or other acceptable gland arrangements.
2. (2) Each compartment must be provided with a mechanical exhaust system capable of ventilating the compartment with a complete change of air every 3 minutes. The intake duct or ducts must be of a sufficient size to permit the required air change. The exhaust duct or ducts must be located so as to remove vapors from the lower portion of the space or bilges.
3. (3) The ventilation outlets must terminate more than 10 feet from any opening to the interior of the vessel that normally contains sources of vapor ignition. The ventilation fan must be explosion-proof and unable to act as a source of ignition.
4. (4) Cargo pumps must not be installed in the cargo tank compartment unless the drive system is outside the compartment. Suction pipelines from cargo tanks must be run directly to the pump, but not through working or crew spaces of the vessel.
5. (5) Tanks must be located so as to provide at least 15 inches of space around the tank, including top and bottom, to permit external examination.
6. (6) Shutoff valves must be provided in the suction lines as close to the tanks as possible. Valves must be installed so as to shut off against the flow. Remote control of the shutoff valve must be provided where the examiner deems necessary.
(i) Exemption for older vessels. Tanks, containers, and associated piping systems in use prior to December 1, 1969, on a vessel the construction of which was contracted for before May 31, 1976, are exempt from the requirements of this section provided they are maintained in a condition that the Officer in Charge, Marine Inspection, finds satisfactory, and provided that major repairs or replacement of exempted equipment and systems is in accordance with this part.