In self defence, I know next to nothing about the UV editor in Carrara. Having said that ... After converting the object to get it into the vertex editor [I have to do that to get at the UV's right?] I can look at the texture map in the UV editor and if the original oject was imported as .obj the initial UV mapping [as "Custom"] in the editor looks like a regular grid mapped texture. By regular I mean rectangular UVs mapped to a rectangular grid. If I apply any other kind of mapping to the object the rectangular UV to grid relationship disapears and the pipe curvature becomes mapped at various projected angles to the grid. And I can't get the initial "Custom" mapping back. If the object is imported as .step and converted in the vertex editor, the initial UV mapping is [or looks] pretty scrambled. Various box mapping projections will lay out the object so its recognizable, but not to the extent where I could convince myself it was worth the time to map it manually [in that editor at least]. Sorry there's no screen grabs - Carrara is on another computer here without a connection.