46 CFR §35.01-25

1. (a)The installation of magnesium sacrificial anodes in cargo tanks utilized for the carriage of flammable or combustible liquids in bulk is prohibited.
2. (b)A sacrificial anode using an aluminum alloy will be permitted in cargo tanks under the following criteria:
   1. (1)The maximum allowable energy that can be developed by a falling anode shall be 200 foot-pounds.
   2. (2)No anode shall be installed more than 6 feet above the bottom of the tank. Special consideration will be given when structural design prevents the anodes from falling in event of failure of the attachments.
   3. (3)Each anode shall have at least two welded or bolted connections to the supporting structure. Special consideration will be given to proprietary attachments which provide equally safe installations.
   4. (4)The plans of the anode installation and a chemical analysis of the alloy composition shall be submitted for approval. The anode should be magnesium free and the silicon content limited to trace amounts.
   5. (5)The recommended construction of the anode should utilize a mild steel core with necessary attachments. Other types may be used but will require special consideration.
3. (c)Sacrificial anodes using materials other than those having aluminum and/or magnesium in whole or in part are permitted.