To clarify it more, it is a composite pipe made of PE liner, fiber and PE jacket. But the jacket and the liner is made of HDPE. Tg for HDPE is around -90C. But if you guys can give me a bit more specific idea regarding using HDPE pipe at -40C and there will be brine in the pipe, that will be great.
Usually a plastic retains decent impact resistance down to about 20°C above its Tg so if PE has a Tg of -90°C then I would expect it to be fine at -40°C. There is a lot of experience on PE pipes containing water so you can get advice from the PE manufactures such as Borealis and Basell. It's especially important to choose the right antioxidant package for pipes because it has been shown that the antioxidants are easily extracted out of the pipe and into the water, leaving the pipe unprotected.
