(Fluid Flow) The degree to which a concentric tubing string is decentralized within an annulus with consideration for calculating the effects of frictional pressure loss. An eccentricity value of 0. 0 indicates perfectly centralized tubing within the annulus. (Tube Mill) A condition of tubing geometry in which the OD and ID axes are not coincident, resulting in wall thickness variation around the circumference at a given section plane.