46 CFR 151.50-32: Anhydrous ammonia cargo requirements
Last reviewed: October 14, 2026
This section sets requirements for carrying anhydrous ammonia. It covers where tanks may be installed, banned materials and joints, ventilation, grounding, water fog for leaks, and respiratory protection during transfer. It also says the requirements of § 151.50-30 for compressed gases apply to anhydrous ammonia.
What it says
Anhydrous ammonia tanks may be installed in the bulk liquid cargo tanks if the liquid surrounding the enclosed tanks meets the listed chemical and physical properties.
46 CFR 151.50-32(a)“The anhydrous ammonia tanks may be installed in the bulk liquid cargo tanks provided the liquid surrounding the enclosed anhydrous ammonia tanks complies with the following chemical and physical properties:”
Copper, copper alloys, and copper bearing alloys must not be used for tanks, pipelines, valves, fittings, and other equipment that may contact anhydrous ammonia liquid or vapor.
46 CFR 151.50-32(b)“Copper, copper alloys, and copper bearing alloys shall not be used as materials of construction for tanks, pipelines, valves, fittings, and other items of equipment that may come in contact with anhydrous ammonia liquid or vapor.”
Threaded joints are not permitted for pipe diameters exceeding 2 inches, and brazed joints are prohibited.
46 CFR 151.50-32(c)“Threaded joints are not permitted for pipe diameters exceeding 2 inches. Brazed joints are prohibited.”
All enclosed spaces containing cargo tanks fitted with bottom outlet connections must have mechanical ventilation of sufficient capacity to assure a change of air every 3 minutes.
46 CFR 151.50-32(d)“All enclosed spaces containing cargo tanks fitted with bottom outlet connections shall be provided with mechanical ventilation of sufficient capacity to assure a change of air every 3 minutes.”
Each cargo tank must be electrically grounded to the hull.
46 CFR 151.50-32(e)“Each cargo tank shall be electrically grounded to the hull.”
When transferring cargo, a hose must be connected to a water supply so water fog may disperse leaked ammonia vapor. Shore facilities can meet this requirement.
46 CFR 151.50-32(f)“When transferring cargo, a hose shall be connected to a water supply so that if leakage of anhydrous ammonia occurs the vapor may be dispersed by the use of water fog.”
During cargo transfer operations, every person on the vessel must carry or have close at hand a canister mask approved for ammonia, or each person must carry a respiratory protective device meeting the text's requirements.
46 CFR 151.50-32(g)“During cargo transfer operations, every person on the vessel shall carry on his person or have close at hand at all times a canister mask approved for ammonia”
Common questions
Can copper be used in anhydrous ammonia piping or tanks?
No. Copper, copper alloys, and copper bearing alloys must not be used for items that may contact anhydrous ammonia liquid or vapor.
“Copper, copper alloys, and copper bearing alloys shall not be used as materials of construction for tanks, pipelines, valves, fittings, and other items of equipment that may come in contact with anhydrous ammonia liquid or vapor.”
How often must air be changed in spaces with ammonia cargo tanks?
Enclosed spaces containing cargo tanks fitted with bottom outlet connections must have mechanical ventilation sufficient to change the air every 3 minutes.
“All enclosed spaces containing cargo tanks fitted with bottom outlet connections shall be provided with mechanical ventilation of sufficient capacity to assure a change of air every 3 minutes.”
Are brazed joints allowed in anhydrous ammonia piping?
No. Brazed joints are prohibited. Threaded joints are also not permitted for pipe diameters exceeding 2 inches.
“Threaded joints are not permitted for pipe diameters exceeding 2 inches. Brazed joints are prohibited.”
The text of 46 CFR 151.50-32
Electronic Code of Federal Regulations (eCFR), current as of March 31, 2026 · Read it on eCFR
Ammonia, anhydrous
(a) The anhydrous ammonia tanks may be installed in the bulk liquid cargo tanks provided the liquid surrounding the enclosed anhydrous ammonia tanks complies with the following chemical and physical properties:
(1) Boiling point above 125 °F atmospheric pressure.
(2) Inert to ammonia at 100 °F at atmospheric pressure.
(3) Noncorrosive in the liquid and vapor phase to the ammonia tanks and piping.
(b) Copper, copper alloys, and copper bearing alloys shall not be used as materials of construction for tanks, pipelines, valves, fittings, and other items of equipment that may come in contact with anhydrous ammonia liquid or vapor.
(c) Valves, flanges and pipe fittings shall be of the tongue and groove or raised-face type, fitted with suitable gasket material. Welded fittings shall be used wherever possible and the number of pipe joints shall be held to a minimum. Threaded joints are not permitted for pipe diameters exceeding 2 inches. Brazed joints are prohibited.
(d) All enclosed spaces containing cargo tanks fitted with bottom outlet connections shall be provided with mechanical ventilation of sufficient capacity to assure a change of air every 3 minutes.
(e) Each cargo tank shall be electrically grounded to the hull.
(f) When transferring cargo, a hose shall be connected to a water supply so that if leakage of anhydrous ammonia occurs the vapor may be dispersed by the use of water fog. This requirement can be met by facilities provided from shore.
(g) During cargo transfer operations, every person on the vessel shall carry on his person or have close at hand at all times a canister mask approved for ammonia or each person shall carry on his person a respiratory protective device which will protect the wearer against ammonia vapors and will provide respiratory protection for emergency escape from a contaminated area resulting from cargo leakage. This respiratory protective equipment shall be of such size and weight that the person wearing it will not be restricted in movement or in the wearing of a lifesaving device.
(h) [Reserved]
(i) The requirements of § 151.50-30 for compressed gases are also applicable to the shipment of anhydrous ammonia.
Sections it refers to
The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of March 31, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.