Fatigue analysis of brazing structures with fin-plate-side bar in Liquefied Natural Gas (LNG) heat exchangers under cryogenic conditions

The purpose of this study is to evaluate the fatigue life of heat exchangers used for Liquefied Natural Gas (LNG) and to ensure its structural safety, the alternating stress of brazing structures under cryogenic conditions was analyzed with a Finite Element Model (FEM). Stress concentrations occurred at the brazed joint with a maximum alternating stress amplitude of 153.45 MPa. The fatigue life of brazed structures during the continuous cool-down and heat-up conditions was evaluated based on the ASME standard and the maximum alternating stress amplitude. Meanwhile, structure parameters have been analyzed for their influence on fatigue life. There are four main structure factors to influence the life cycle: the brazing seam, the fin thickness, the fin distance, and the fin height. The life cycle will decrease with increasing the fin distance, fin height, and brazing seam thickness, and it will increase with increasing the fin thickness. In addition, in order to predict fatigue life, a calculating model has been established based on the main factors. Finally, the fatigue life of brazing structures was also tested by experiment, and the microstructure was also analyzed for the fatigue fracture surface. It is clear that brittle fractures along the brazing seam and ductile fractures at the fin roots should be the primary failure modes. The study provides a base for LNG aluminum heat exchanger design, manufacture, and safe operation.