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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.

In order to ensure the safe operation of heat exchangers in the Liquefied Natural Gas (LNG), the stress analysis model of aluminum Plate-Fin Structure (PFS) is established based on the thermal-elastic-plasticity theory. The residual stress distribution of PFS and its influence on the structural strength is analyzed by the thermal-structural coupling method. The results indicate that the residual stress distribution of PFS is very complex, and the residual stress reaches the peak at the Brazed Joint (BJ). Due to the equivalent stress at BJ near the fin is higher than that at BJ near the plate, cracks are more easily produced at BJ near the fin. Therefore, the existence of residual stress has a negative impact on PFS, which may increase the possibility of strength failure at BJ under the typical operating conditions (normal operation, cut-down and heat-up) of the heat exchanger. In addition, the residual stress gradually decreases with the brazing cooling rate decrease. The residual stress within the PFS will be effectively reduced by properly reducing the brazing cooling rate, which can slow down the strength failure of the PFS. The above research results will provide an important basis for the design and safe operation of the aluminum plate-fin heat exchanger.