Stress Analysis and Sealing Performance of Pipe Flange Connections With NiTi Shape Memory Alloy Gasket

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. Nickel-Titanium shape memory alloy (NiTi alloy) shows an excellent elasticity and is expected to be applicable as a gasket. The authors have already evaluated the sealing performance of the pipe flange connections with NiTi gaskets. The results revealed that NiTi alloy showed a superior sealing performance to the conventional aluminum gasket. However, the sealing performance of the connection depended on the ambient temperature due to the change in physical properties like the elastic modulus and the thermal expansion coefficient of NiTi alloy. In this paper, the stress distribution was analyzed with 3D FEM and the effect of temperature in the sealing performance was evaluated. In the analysis, the particular element code was adopted for analyzing the deformation behavior of NiTi alloy gasket. The elements worked well in the analysis and helped to evaluate the sealing behavior of the flange connections. According to the analysis, the gasket contact stress decreased as increasing the temperature because of the lower thermal expansion of NiTi alloy than that of austenitic stainless steel of which the flange and bolt material were made. On the other hand, the FEM analysis suggested that the increment of elastic modulus of NiTi alloy compensate the reduction of compression strain of the gasket due to the difference of thermal expansion between gasket and flange. As a result of the ex-experimental study and FE analysis, the recommendable assembling process for NiTi alloy gasket was proposed.