Creep damage and crack propagation behavior of printed circuit heat exchanger manufactured by diffusion welding: from material to structure

Abstract

The printed circuit heat exchanger (PCHE) is extensively used in several applications due to exceptional compactness and heat transfer efficiency. However, the dominant failure mode of PCHE is creep fracture in its diffusion welding joints. Therefore, an accurate prediction of the creep crack propagation behavior for diffusion welding joints is essential for assessing the life of PCHE. In this paper, based on the research route from material to structure, the creep properties of 316L stainless steel base metal and its diffusion welding joint are firstly measured. On this basis, a constitutive model incorporating a time-hardening term for describing the creep damage is established. Furthermore, the creep damage and service life of the PCHE structure under working conditions (600 °C, 20 MPa) are analyzed, along with the effects of structure factors on the creep crack propagation behavior. The results show that the initial decelerating stage and the steady state stage play a dominate role in the creep curve of the diffusion welding joint, differing from the base metal's creep curve. Besides, the creep rate of the joint is approximately 30 times that of the base metal. The established creep damage constitutive model effectively characterizes the creep crack propagation behavior of diffusion welding joints. The maximum creep strain occurs at the weld metal and continuous operation for 100,000 h can be achieved at the designed working condition (600 °C, 20 MPa). For the purpose of lifetime extension by restraining the creep crack, it is recommended to increase the spacing and fillet radius while reducing the diameter during design process.

Keywords

• Creep crack propagation
• 316L stainless steel
• Diffusion welding
• Printed circuit heat exchanger