SEALING PERFORMANCE OF PIPE FLANGE CONNECTIONS WITH SHAPE MEMORY ALLOY GASKETS UNDER INTERNAL PRESSURE

摘要

Due to the long-term durability and the excellent resistance to aging degradation, metal gaskets are expected to give a longer life compared to conventional polymer gaskets. However, the nature of high elastic modulus of the metal reduces the sealing performance at interface. On the other hand, shape memory alloys (SMA) like nickel - titanium (Ni-Ti) alloy have a super elasticity and an excellent deformation capability with relatively low elastic modulus as a metal. Therefore, Ni-Ti SMA is expected to show an excellent performance as a gasket. In order to evaluate the applicability of Ni-Ti SMA to gasket, experimental and numerical analysis were conducted in this study. As an experimental evaluation, the new gasket constants and the tightness parameter proposed by PVRC (Pressure Vessel Research Council) were measured by the leakage tests. The constants and the tightness parameter of Ni-Ti SMA gasket were superior to those of aluminum gasket. The numerical analysis revealed that the clamping temperature highly affected on the performance of Ni-Ti SMA gasket because the stress-strain behavior of Ni-Ti SMA strongly depended on the temperature. Since the Ni-Ti SMA has a softer phase at low temperature, e.g. less than 11°C (As point), the flange connection initially clamped at low temperature showed a higher sealing performance. In addition, the heat cycle test with the cycle of the initial clamp temperature (0 or 20°C) to 40°C also suggested that the lower clamp temperature yielded a higher contact force due to the thermal expansion effect.