I've got a simple pipe geometry. Everytime I'm creating an ogrid i got negative volumes/elements on the inlet and outlet surfaces. the pre-mesh looks perfect but the pre-mesh quality check show me these elements, also i cant see them normally. What am I doing wrong. The geometry surface normals show all outside the domain. Please help me, its urgent.

Run the mesh checker/fixer.

I did. No change.

Post picture of your geometry/topology and resulted mesh

It almost sounds like you have pancaked blocks at the ends of the pipe. When you do the O-grid make sure you add the faces at the pipe ends so the O-grid passes through the ends.

If you turn on the Blocks make sure you don't have 0-thickness blocks at the ends of the pipe. If it turns out that you do - you can delete them.

Thank you myron. I found those pancaked blocks. Now the mesh is as fine as it looks like.