I have similar issue. When I look on my pipe in cross section is looks like this:

When I look on pipes in floor plan (Detail level: Fine) looks like this:

When I look on pipes in floor plan (Detail level: Coarce) I see only symbols of changing the height of the pipe when I use bends 90 degree, 45 degree bends looks like straight line:

Is something wrong in my pipes family?

this issue is related to how Revit displays symbolic lines in a family. Only items that are parallel to the ref level plane will appear in a view - when the object, such as an elbow or tee, is rotated any other angle (or to an angle where the rise drop style is not perpendicular to the view), the symbology won't appear. 

the Fix is for autodesk to allow symbolic lines (not just model lines) to appear in more than one view plane. There is a similar setting in AutoCAD MEP fittings now, where you can add 2D symbology to the top, left and front planes - a similar mehtod woud fix this. If anyone wants to add this to the Idea's forum, we can vote it up...!

BTW - the only fix to this is to create detail symbols to represent how you want the fitting to appear, and attach it to the single line of the pipe...a CAD method fix.

This is strange, pipe tee connected 45 will give some symbol, I think autodesk should improve this in next revit update.

That's interesting - I'm betting those are model lines instead of symbolic lines. You can check this by opening the family up and taking a look at the ref plane view.

Sorry for the very late replies.

Not quite, more like explained by another user further down in this thread. It is for vertical bends. I "fixed" it by simply adding a detail line manually everywhere I have bends that are not displaying properly.

I have since learned that Revit does not have an option to display bends like that in single line view so adding them manually is the only solution.