SELECTION OF MATERIALS FOR REFRIGERANT
Copper-a material used almost everywhere for halocarbons pipelines, without the low-temperature limit in industrial refrigeration practice. For ammonia systems, as copper is inadmissible, all steel pipes in one form or another. While aluminum is often used for tubes of air-cooling coil is hardly ever used for liquid and steam pipelines in the plant construction. Cast iron pipes should not be used and wrought iron pipe should not be used for the liquid line.
The most commonly used steel for ammonia systems carbon steel A53 or A106. Type A53 F butt-welded and should not be used, on the other hand A106 seamless, so is acceptable. ANSI/ASME Refrigeration Piping Standard14 allows the use A53 or A106 down temperature -29C (-20F). One of steels permitted ANSI/ASME standard below this temperature type A333. Compared with A53 or A106, A333 tube about three times more expensive, the cost factor is even more valves and fittings. A53 and A106 steel can be used below -29C (-20F) provided that they pass tests on the influence of the temperature under which they will operate.
It is obvious that the impact testing adds to the cost.
Another option, the proposed standard for designing circle or longitudinal tensile stresses, 40% of the allowable voltage for a given material. Refrigeration interests in recent years, there were attempts to get A53 and A106 steels approved below -29C (-20F) operation on the grounds that the ammonia refrigerant pressure to be in the range of atmospheric, so that the pressure in the pipe will be minor. At temperatures lower than -46C (-5F) many designers uses stainless steel for ammonia and hydrocarbons.
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