You mean give thickness to the pipes?
A little bit cumbersome, you can do it with vanilla GH components. And you’ll need just one component(Offset Surface) with pufferfish plugin.
If you make caps, they are already closed polysurfaces. My solution is for pipes which have no caps(single surface). It only works with 0=None type of caps.
You need to understand the basic properties and terminology of each geometry type.(surface, polysurface, brep, solid, mesh…)