Reliability analysis of stainless steel/carbon steel double-layered tube on the basis of thermal deformation behavior

The thermal expansion of pipes depends on both the temperature of the pipe and the expansion coefficient of the piping material at the operating temperature. In the case of a double-layered tube consisting of two different tube materials, the thermal deformation behaviors are dependent on the relative tube sizes, thermal expansion coefficients, and the mechanical properties of the inner and outer tubes. For the safe and reliable application of double-layered tubes that are fabricated by hydroforming, the thermal stress in circumferential direction and the gap between the inner and outer tubes need to be analyzed over a wide range of temperatures (−50°C∼200°C). As it is difficult to measure the thermal stress and the gap between tubes at operating temperature, this study has analytically investigated the thermal deformation behavior of a double-layered tube. From the analytical model, the effect of hydraulic pressure, residual stress, and the relative sizes of the inner and outer tubes on the resultant thermal deformation, such as the circumferential thermal stress and the gap between inner and outer tubes, has been analyzed. The analytical results provide a theoretical basis for determining the reliable operating temperature of double-layered tubes.