Reynolds number through a pipe

Jonny6001

Hello, can someone tell me how the reynolds number for flow through a pipe change along it's length? Is the only method that the boundary layer gets thicker along the pipe so the freestream velocity increases? Assuming no gas temperature change along the pipe's length.
From thinking of the actual definition of the reynolds number, the ratio of inertial to viscous forces, I can see that the higher free stream flow in the thicker boundary layer regions would increase the local inertia force of the gas.

I would like someone just to clarify.

Thanks a lot.