The influence of residual stress for the strength of plate-fin structures in the typical operation process of Liquefied Natural Gas (LNG) heat exchanger

Abstract

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.