rhino will not find the red intersection.
this is why boolean operations (and trim @theoutside) both fail.
to get the intersection:
_extractSrf (both)
_insertKnot Automatic, 4 or 5 times (EDIT: both directions)
now
_intersect will give a longer / closer result.
_extend the intersection curve
make sure the endpoint is at the midpoint of the arc (move the CV or SetPt)
Screenshot: pipe-like surfaces after inserting Knots.
(before extend)
The surfaces with endless Knots are only to generate the curve.
now trim works with that curve for both (original) surfaces.
Pipes_fixed.3dm (1.8 MB)
… and for lazy people with big bricolage risk:
construct the curve as above
use the curve to split the faces in question (_splitFace Select Curve option)
delete the part of the surface that is not needed in the final solid.
_booleanUnion (the bricolage action)
_explode
_join
Pipes_fixed_bricolage.3dm (1.2 MB)
happy modelling - kind regards -tom