Materials of construction for refrigeration systems relate specifically to the type of refrigerant used. Some of the basic guidelines are:
· No copper or copper-based alloys can be used with ammonia refrigeration systems. Where SO2, H2S, or similar corrosive chemicals are in the process side or are present in the atmosphere, copper or copper-based alloys are unsuitable.
· Generally, copper and copper alloys can be employed with hydrocarbon and halocarbon refrigerants; however, for most systems steel piping and components are recommended.
· Due to the ambient temperature vapor pressure of most refrigerants, the refrigeration system is normally designed for 250 psig or greater. The low temperature components of the system will operate at temperatures and coincident pressures far below the design pressures. Generally speaking, carbon steel can be used to –20°F. The ASME pressure vessel code section 8 addresses the issue of material selection and impact testing for systems operating below –20°F. Certain provisions in that code may allow carbon steel use for components which operate at pressures less than 25% of design pressure. In many applications, Charpy impact testing will be required.
· The ANSI B31.3 pipe code is generally used for most refrigeration systems in gas processing plants. This code has some provisions for use of materials to –50°F which are normally limited to –20°F and should be consulted for application in this area. There also exists an ANSI B31.5 “Refrigeration Piping Code” which has been used in some applications.
· Various alloys and aluminum are normally used for low temperature operations and may be economically advantageous at temperatures above –20°F.