When creating an intersection curve from these two pipes, the curve stops at the seam, then punctuates itself with a point at the far end of the intersection. If you move the seam so it doesn’t fall within the intersection, the full curve is drawn correctly (and not the point).
Rhino 6.13.19043.11071, 12/02/2019
Intersection curve stops at seam.3dm (167.4 KB)