When functions such as Swap Part Graphical, Swap Part Dialog, Nudge Structure, Curve Pipe, Straight Pipe doesn't work on one pipe or structure the most common reason is errors with the Parts list. Go through the steps below to find the most common solutions
Check Pipe Network Catalog
Most issues when a structure can't be created or swapped out, arise from the Pipe network catalog being incorrectly set. Remember that the Parts List is stored in the drawing, but it connects to the Pipe Network Catalog when you actually interact with the object.
This also means that if you use a custom Pipe Network Catalog, make sure it is distributed to all designers involved in the project!
Check the Part in the Parts list
Sometimes the part has been reset in the parts list. Go into the parts list, right-click on the part that you have issues with and select Edit. Make sure that you can do Edit on your object, and that the settings are correct. If you have trouble accessing Edit, it is usually because the Part catalog is not set correctly. If this is the case, you will most likely see a message on the commandline about "Unable to load part family" - this is an indication that the part catalog is not correct.
Also remember that part catalogs can be updated, so if you are sure that you have the correct catalog, it is a good idea to verify that you also have the right version/date on the part catalog.
Check Pipe or Structure Style
In some cases the object is altered, but the style doesn't show it. When you verify that the function does what it should, make sure you check in Structure or Pipe Properties, and not just go on the visual look of the object.