Anhydrous Ammonia Storage & Tank Compatibility

Storing Anhydrous Ammonia? Start Here

Anhydrous ammonia (NH₃) is one of the most widely produced industrial chemicals in the world, serving as the backbone of nitrogen fertilizer, a key feedstock for plastics and explosives, and a high-efficiency industrial refrigerant. "Anhydrous" means water-free: it is a clear, colorless liquefied gas with a sharp, penetrating odor, stored under its own vapor pressure of roughly 114 psig at room temperature. It is toxic by inhalation, corrosive to skin and eyes, and forms a strongly alkaline solution the instant it contacts moisture. Because it is a pressurized liquefied gas, anhydrous ammonia is handled in steel ASME and DOT pressure vessels, not in open or atmospheric tanks. Understanding its corrosivity, flammable range, and material behavior is essential for any operation that produces, stores, transfers, or applies it in the field.

Is Anhydrous Ammonia Compatible With Polyethylene (HDPE / XLPE) Tanks?

This is a two-part answer, and getting it right matters for safety. Chemically, polyethylene resin resistance charts rate both HDPE and crosslinked polyethylene (XLPE) as resistant to ammonia and to aqueous ammonium hydroxide, so the polymer itself does not degrade on contact. Mechanically, however, anhydrous ammonia is a liquefied compressed gas stored under pressure, and atmospheric polyethylene tanks are not pressure-rated vessels. Using a standard poly tank for liquefied anhydrous ammonia is unsafe and not code-compliant; this service belongs in steel ASME or DOT pressure tanks. Where polyethylene is appropriate is for water-diluted ammonia solutions (ammonium hydroxide) handled at atmospheric pressure, where HDPE and XLPE rate as Suitable. For any diluted-ammonia poly tank application, vent properly, confirm gasket and fitting materials (EPDM, not Viton or copper alloys), and verify the specific concentration and temperature against the resin manufacturer's chemical resistance chart before placing into service.

Material compatibility at a glance

Anhydrous ammonia is stored and transported almost exclusively in steel pressure vessels (ASME / DOT tanks and nurse tanks) because it is a liquefied compressed gas. Carbon steel, stainless steel, PTFE, PVDF and EPDM are the workhorse materials. Copper, brass, bronze, zinc and galvanized surfaces must be avoided because ammonia causes stress-corrosion cracking of copper alloys and attacks zinc. While HDPE and crosslinked polyethylene are chemically resistant to ammonia, atmospheric polyethylene tanks are not pressure-rated and are therefore unsuitable for liquefied anhydrous ammonia; poly tanks are appropriate only for water-diluted aqueous ammonia (ammonium hydroxide) at atmospheric pressure.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Toxic by inhalation: ammonia vapor is toxic (H331) and severely irritating; provide adequate ventilation, gas detection, and respiratory protection rated for ammonia.
• Corrosive contact: causes severe skin burns and eye damage (H314 / H318). Liquid contact also causes cryogenic frostbite because it flashes off cold. Wear chemical goggles, face shield, and ammonia-resistant gloves and suit.
• Flammable gas under pressure: flammable range is roughly 15 to 28 percent in air (H220 / H280). Eliminate ignition sources and protect vessels from heat.
• Never use copper, brass, bronze, zinc, or galvanized components in ammonia service; ammonia causes stress-corrosion cracking of copper alloys and attacks zinc.
• Store only in rated steel pressure vessels (ASME / DOT). Do not transfer liquefied anhydrous ammonia into atmospheric or polyethylene tanks.
• Have an emergency water source and eyewash available; keep a current Safety Data Sheet on site and train personnel on ammonia release response.

Common questions

Can I store anhydrous ammonia in a polyethylene tank?

No. Anhydrous ammonia is a liquefied compressed gas stored under its own vapor pressure (about 114 psig at room temperature), and atmospheric polyethylene tanks are not pressure-rated vessels. Liquefied anhydrous ammonia must be stored in steel ASME or DOT pressure tanks. Polyethylene is only suitable for water-diluted aqueous ammonia (ammonium hydroxide) at atmospheric pressure.

Is anhydrous ammonia corrosive to steel?

Dry anhydrous ammonia is essentially non-corrosive to carbon and stainless steel, which is why steel is the standard material for ammonia pressure vessels and nurse tanks. The serious corrosion concern is with copper, brass, bronze, zinc, and galvanized surfaces, which ammonia attacks and which can fail by stress-corrosion cracking.

What is the NFPA 704 rating for anhydrous ammonia?

Per the CAMEO Chemicals (NOAA) datasheet, anhydrous ammonia is rated Health 3, Flammability 1, and Instability 0, with no special hazard symbol. The Health 3 reflects its toxicity and corrosivity, while Flammability 1 reflects that it must be preheated or strongly ignited within its flammable range to burn.

Why must copper and brass be avoided with ammonia?

Ammonia, like other amines, causes stress-corrosion cracking of copper and copper alloys such as brass and bronze, and it also attacks zinc and galvanized coatings. Fittings, valves, gauges, and seals in ammonia service should use steel, stainless steel, PTFE, PVDF, or EPDM instead.