Problem with tube render/display

Hi! Sorry for a dummy question. But I have a problem. My object displayed incorrectly. I thinked that its problem with my comp’s CPU, but another object displayed well. Sorry for my awful english, it isn’t my native. Thank you!

There’s nothing wrong with your CPU. You must model both the inside and the outside. If you did model the inside, then you need to make sure the surface normals are pointing outward.

It looks like you does not have any light in scene as well so you don’t see any shading on it. Hard to judge normal facing without light but for me it seems ok.