How can I model the grooves of a ventilation pipe?
Add a cylinder with no fill, then subdivide it in the middle with Ctrl+R. Bevel the loopcut with Ctrl+B and set its thickness. Next inset the faces with I to create extra loopcuts for subsurf creasing. Then extrude the loop of faces (E) and scale it along Z and Y axis only (S,Shift+X). Repeat it twice, then inset the faces again. Finally add a Subsurf Modifier and apply the smooth shading. One segment is ready.