Understanding Fittings in Ammonia Absorption Refrigeration Systems

Ammonia absorption refrigeration systems use ammonia (NH₃) as the refrigerant. These systems are known for their ability to operate using heat energy, making them suitable for applications where waste heat is available or electricity is expensive.

Selecting the correct materials for components like fittings, pipes, and vessels is crucial in any refrigeration system, particularly when using a reactive refrigerant like ammonia. The material must be compatible with the refrigerant and any other substances present in the system (like water in absorption systems).

Material Compatibility with Ammonia

Ammonia is highly corrosive to certain metals, especially those containing copper. This is a primary factor in determining the materials used for system components and fittings.

• Copper and Brass: Copper and alloys containing copper, such as brass, react with ammonia. This reaction can lead to the formation of complex compounds, corrosion, and weakening of the material. Therefore, copper and brass are unsuitable for use with ammonia and are strictly avoided in ammonia refrigeration systems.
• Aluminium: Aluminium's compatibility with ammonia can depend on conditions like temperature and the presence of water. However, it is generally not the preferred material for critical components like high-pressure fittings in ammonia systems due to potential corrosion risks.
• Steel (Cast Steel or Forgings): Carbon steel and alloy steels are highly resistant to corrosion by ammonia. This makes steel, including cast steel and steel forgings, the standard material for pipes, fittings, valves, and vessels in ammonia refrigeration systems, especially where high pressures and temperatures are involved. These materials provide the necessary strength and durability while remaining compatible with ammonia.

Conclusion on Fittings Materials

Based on the compatibility requirements and the corrosive nature of ammonia towards certain metals, fittings in ammonia absorption refrigeration systems are made of materials resistant to ammonia.

Comparing the options:

Therefore, fittings in ammonia absorption refrigeration systems are typically made of cast steel or forgings due to their excellent resistance to ammonia corrosion and sufficient mechanical strength.