I have a model of a heat exchanger that has very complex bends. We will not be able to bend this out of one length of tube so I need to break up the model into small parts that we can weld together.

When I use Split function I get weird results.

Splitting it here...

...Gives me this part (there are others that are just slivers of the tubing).

Any help would be appreciated.

If you are using the Split function and choosing a plane it will cut through the whole model along that plane for infinity, no matter how big the plane looks.

Unless you choose otherwise. I chose to only split the top chunk

There is my result.

Try is one plane at a time... it might work.