How can the end of a cylinder (pipe) be fixed in such a manner that allows for radial expansion (thermal expansion) but does not allow the center-line of the cylinder to move in any direction (X-, Y-, or Z-axis)?

Specifically, I am working with an expansion loop. If left insufficiently restricted, the pipe end will move any all 3 directions and thus provide false stress results.

Applying a Fixture Geometry fixture also restricts the thermal expansion, providing falsely high stress results.

Applying Fixtures on Cylindrical Faces can allow for thermal expansion, but restricts displacement in 1-axis only.

Is there any way to grab an axis or reference point at the center-line of the pipe to restrict displacement without restricting radial expansion?