Carbon dioxide, refrigeration fitting, durability testing, explosive decompression, carbonic acid
Successful implementation of R744 (CO2) as a refrigerant on a large scale and its introduction to new applications has motivated the development of new system components tailored specifically for use in high-pressure R744 systems, including reliable, low-cost refrigeration fittings. One option for fittings to be used in R744 systems are quick and reliable press fittings. Previous research has shown that this type of fitting can undergo extended vibration and thermal (pressure and temperature) cycling without compromising the fitting. This paper investigates the durability of stainless steel press fittings designed specifically for R744 systems, with particular focus on the effects of rapid decompression and carbonic acid exposure on the fittings. Rapid decompression is of concern due to the tendency of O-ring material to absorb CO2 molecules at high pressure and temperature, resulting in possible expansion and bursting of the O-rings when pressure drops and the CO2 absorbed by the O-rings attempts to escape very rapidly. Additionally, the presence of moisture in an R744 system can result in the reaction of CO2 and H2O, resulting in the formation of carbonic acid; the exposure of the refrigeration system components to this weak acid over time can compromise parts different of the refrigeration system, possibly including joints. The effects of decompression and acidity on stainless steel press fittings and their O-rings have been tested and are reported in this paper.