Hi Ed - so it looks like your tube pattern before you flow it is not all the way cleaned up - it's got some pieces still on the interior portion of it making it a kind of self-intersecting object instead of an empty interior.

Here's an example area - check out this edge right here:



Note this edge here:



See how that edge is kind of sunken into the object - it's part of a surface that is on the inside area of the object, the outer pieces of the pre-flowed flat object are not all trimmed with one another, they've ended up only kind of partially cut with each other leaving various internal pieces still in there.

Once you have a self-intersecting object like that it will confuse the booleans quite a bit trying to use it as a cutting object.

So basically the flat object itself seems to need some tuneups before it is flowed.

- Michael