NiTi shape memory alloy pipe couplers for ultra-high vacuum systems: Development and implementation

Abstract

Novel Nickel-Titanium (NiTi)-based shape memory alloy (SMA) pipe couplers were designed and developed. They are suitable for room-temperature ultrahigh vacuum (UHV) systems and provide a quick and compact solution at reasonable cost. Their use is particularly interesting for restricted-access areas of particle accelerators as their installation/dismounting can be performed remotely by temperature variations. A NiTi SMA with suitable composition was selected. NiTi couplers with different diameters in the range 30-135 mm were manufactured and thermo-mechanically trained to exhibit a proper two-way shape memory behaviour which comply with the strict operative constraints for coupling applications in room temperature vacuum sectors. The connectors are easily implementable as they were designed to be compatible with commercially available flanges (DN16, DN25, DN100) used worldwide in vacuum systems. The effect of the SMA joint geometry on the thermo-mechanical response and vacuum performance was investigated by numerical studies and experimental analyses such as strain-gauge, extensometer and leak-tightness tests performed under different operating conditions including static axial loads and multiple thermal cycles. It was demonstrated that NiTi-based connectors can be thermally mounted upon heating and can guarantee the leak tightness of the vacuum pipe within a suitable temperature window. The thermal dismounting was also verified by cooling the couplers down to subzero temperatures (lower than -40 °C). Possible use of these connections at European Organization for Nuclear Research (CERN) is foreseen in vacuum assemblies installed in high radioactive areas, like those nearby particle collision points and beam collimators. Thanks to their compactness, SMA couplers are also of great interest for connecting beam pipes with small aperture such as those studied for the electron-positron future circular collider (FCC-ee) and next-generation synchrotron light facilities.