Low-GWP refrigerants, flammable refrigerants, mechanical joining methods, durability testing, refrigerant leakage rate
Much concern has been raised recently about the flammability of several low-GWP replacement refrigerant options, such as HFO’s, lower-GWP HFC’s, and flammable natural refrigerant options, regarding the potential leakage or failure of joints in systems using these refrigerants. This paper presents the results of a study investigating the assembly, durability, and leakage rate of different types of field-made joints used in refrigeration and air-conditioning systems. The focus of the project is on flame-free joining methods; in particular, three different types of joints were investigated: Press/crimp fittings, compression fittings, and flare fittings. For each type of joint, two different sizes were used as well as two different tubing materials (copper and aluminum). Brazed copper joints were also investigated as a baseline. Each type of joint was assembled by a combination of both experienced and inexperience refrigeration technicians. A total of 100 of each type of joint (excluding brazed) were assembled, and the results for average assembly time and failed joint assemblies are presented. Durability testing in the form of pressure-temperature thermal cycling, freeze-thaw cycling, and vibration testing was performed on all combinations of joints. Failures observed on each type of joint during durability testing are also presented. Finally, the measured refrigerant leakage rate using R32 is presented for each type of joint.