Looks like at some point in your modeling work flow you wound up with exploded curves. That’s a thing to keep an eye on as you are modeling and weld them if needed.
At this point you can select the geometry, right click on it and choose Soften/Smooth from the Context menu.
Looks like there’s at least one internal face you should delete.
That depends on what you are modeling.
In case of your pipe you could push pull a ring instead of a circle or draw a cross section of the wall and follow me that around a circle…
For more difficult shapes I would use an extension called joint push pull