Here are a couple tips for making open segment turnings. First, I recommend using a turning tool that makes shear cuts, not scraper cuts. A shear cut slices the wood fibers and is less agressive than other tools. There are other ways to get shear cuts, though. Some of the carbide tools have raised burrs and those make nice shear cuts.
The big thing, though, is to not be in a hurry to do any turning and NEVER touch a tool to the row you just added. It is not stable until a row has been added to lock it in place from above and below. The time where the vessel will become the most stable is when the top row (a closed row) is added. At this time, the bowl has a lot of bulk and that top closed row really locks everything in place. If you're like most of us, though, waiting for the last row to start turning is hard. So it is OK to turn as you go as long as you stay away from the last row and as long as you're not trying to take it to the finished wall profile. The additional bulk on the lower rows helps to keep everything together and you'll find that it is easier to turn if you work from the top rows towards the bottom, just as you would if you were turning a solid wood bowl.
The fun is in the learning. Welcome to the community.
Lloyd
I have been working on an open segment bowl but when I was shaping the inside with light cuts it came apart. 
??? Still working on it.