The Einstein Telescope (ET) is a gravitational wave detector of the third generation in preparation in Europe. It is based on six Michelson interferometers enhanced by Fabry–Perot arm cavities, with an arm length of 10 km each. The interferometers will be in underground tunnels in the shape of a 10 km equilateral triangle. The laser beams will travel in ultra-high-vacuum (UHV) pipes. A diameter of roughly 1 m is required to enclose the beams and in total 120 km of these UHV pipes will be required making it the largest UHV system ever built. This study aims to explore alternative materials that can satisfy the stringent requirements of UHV environments while being more cost-effective. A comprehensive analysis of the selected materials is conducted, focusing on their microstructure, weldability, formability, mechanical properties, and corrosion resistance.