difficulty to get a clean geometry

[micheus]

Hi pascalchap
Your file contains only one slice of the main object, so I can't see the problem in your mesh. But, I have some idea about the problem origin. You used the Mirror command to create the entire loop of the object.
Depending on how did you use it you can have some issues on the mesh. It can get some overlapping faces; the mesh can stay open;...;

For details about what happen in these cases take a look on this other thread (same problem as your): help - radial mirror inner faces (the are illustrations)


There are some ways to create the whole object from its slice, but the safest one is by duplicating it (in this case, seven times); select these seven; rotate them 45 degrees by picking the reference axis (in this case the one on the top); deselect one (CTRL+LMB); repeating the rotate command with SHIFT+D; then deselect one and repeat until the last one.
Now, with all slices in the right place; we select all of them and use Weld command. Just pay attention that Weld uses a distance tolerance of 0.001 by default and sometimes it can weld undesired parts of our object. Just undo and access the command with the RMB to change that value.

I attached back your project after I apply the method above to the section you shared and the final shape is OK. It also includes my version in case you want to take a closer look.


Just an observation...
Since your desired object will still be a cylindrical shape, why did you sliced it and made all those procedures?
If the idea was to try adjust the thickness, then you could save a lot of time just using Intrude and make the fine adjusts after.

I used a cylinder to reproduce the object using the section you shared to create the same silhouette. Then applied the Intrude setting a thickness of 0.02 (which was around the one you used).
Although it was not necessary, I sliced it to show you how the section is kept constant (most the time) and then executed that process I commented above to rebuild it.