Shower pipes
#1
#2

There is only one pipe that rises from the valve to the drop-earred elbow where the shower arm screws in. "Cleaning" it is pretty much out of the question. If it is old galvanized and full of corrosion, replace it. But be aware, that will involve opening up the wall from one side or the other so you can get to it!
#4

I'm not a plumber, but if your question is prompted by poor water pressure, try removing your showerhead and cleaning IT out, first, and soak it in vinegar overnight to dissolve hardened minerals.
Run the shower without the head on it to flush line and check pressure/volume. If that is normal, and cleaning the showerhead did not help, just replace the showerhead.
Otherwise, you'll have to replace the pipe, if it's galvanized.
Good Luck!
Run the shower without the head on it to flush line and check pressure/volume. If that is normal, and cleaning the showerhead did not help, just replace the showerhead.
Otherwise, you'll have to replace the pipe, if it's galvanized.
Good Luck!