1) Ctrl+R over a entity (pipe, wall or belt), where you want to start, now you're in building mode.
2) Select the end of the line, will show a area selected, where your line will be builded. If this area have red corners, can't avoid the obstacles, in other case, don't exists obstacles or can be avoided (Underground)
3) With + and - can adjust the width of the line
4) When you selected the area and size where you want to build, use Crtl+R again.

If you want to cancel the line, only ignore it, with Q or select other item