Effect of wall friction on stagnation pressure and temperature

We have incompressible air flowing through a cylindrical pipe, from section A to section B. The process is considered to be stationary.

My theory book says that, because of the frictional losses on the walls of the pipe, the stagnation pressure will eventually decrease from B to A: $$\Delta p_0=p_{0}^{B}-p_{0}^{A} < 0$$

I understand that wall friction actually represents a loss of energy, but I can't see how this loss decreases stagnation pressure.

I'm using these equations: $$p_0^A=p^A+\dfrac{v_A^2}{2c_p}$$ $$p_0^B=p^B+\dfrac{v_B^2}{2c_p}$$

Intuitively, the velocity of the incompressible air will decrease from B to A, but I don't know about the static pressures.

Any help or hint will be greatly appreciated.