Hi 
Here is what I would do :
- Create a straigth pipe (I used an array of cubes)
- Unwrap it from side view using
Project from View (Bounds)(It would fill all the UV surface)
- Use a curve modifier, or wathever, to get the shape you want :
- Then for the shaders :
The output of this group, is 0 or 1, if X of the UV map is greater than 1.
So I use it for example to mix the color :
- And then you just need to animate the X location of the mapping node
from 0 to 1to get what you want :
Here is the file :
pipes.blend (781.7 KB)
See you ++
Tricotou