For the swirling flow created in the suction pipe of centrifugal pumps at partial discharges, the authors evaluated the distribution of shearing stresses by using measured velocity and pressure and compared it with strain velocity. The stress tensor at any point within the pipe is verified to be in proportion with the rate of strain velocity. Although the absolute value of the radial component of velocity exceeds hardly one hundredth that of the axial or rotational component, it contributes considerably to the stress tensor and can not be neglected. Eddy kinetic viscosity of the flow near the pipe wall ranges from 20 to 70 times the kinetic viscosity due to molecular causes.