Assessment of leakage rate and durability of field-made mechanical joints for systems using low-GWP flammable refrigerants (ASHRAE RP-1808)

The conversion of refrigeration and air-conditioning systems to low-GWP refrigerants, such as HFO's, has raised many concerns about the flammability of potential replacement refrigerants, particularly regarding the potential leakage of flammable refrigerant from mechanical joints. This paper presents the results of a study investigating the durability and leakage rate of different types of field-made joints used in refrigeration and air-conditioning systems, focusing on flame-free joining methods and systems with flammable refrigerants. Three different types of fittings were investigated: Press/crimp fittings, compression fittings, and flare fittings. For each type of fitting, two different sizes were used as well as two different tubing materials (copper and aluminum). Brazed joints were also investigated as a baseline. Durability testing in the form of pressure-temperature thermal cycling, freeze-thaw cycling, and vibration testing was performed on all combinations of fittings. Refrigerant leakage rates were also determined for all combinations of fittings.