How to resize the pipe Diameter

[RCP]

How to fix a pipe

Presumably you used Follow Me to make that? If so, you need to set the path and profile up correctly. The first segment of the path needs to be perpendicular to the profile. Also the extrusion will end perpendicular to the last segment. Instead of starting with an arc for the path, you can start with a circle, rotate it so an edge is perpendicular to the profile and then split out the arc. [FM]