This articles demonstrates how to determine pressure losses through drill string.

To determine pressure drop while the drilling mud is passing through a circular pipe (drill pipe and drill collar), you can calculate pressure loss with the following equation:

**Assumptions:**

Turbulent viscosity = 3 cp

Friction factor = 0.378(Q/D)^{-0.14}

The first equation has a coefficient (C) to take into account the friction and the geometry of the bore ID.

Where:

P = pressure loss, psi

L = length of pipe, ft

W = mud density, ppg

Vf = viscosity correction factor

PV = plastic viscosity, centipoises

Q = flow rate, gpm

Di = inside diameter of pipe, inch

C = general coefficient for internal diameter of pipe

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