Hi mat10x,

since Karsten mentioned Iso curves, which works nicely, you don't have to use the Node Editor yet
to archive the same task.

In case you have not done yet, you can try the following:

Use the "Show pts" command on the first profile of the big pipe and then use the "Construct/Curve/Iso/U"
command and snap the Iso curves to the 12 points (or more/less points if you use the "rebuild" command,
typed in the bottom coordinates box).

(Thanks Karsten for the Iso curves tip!)

Regards
Stefan