An optical strain gauge system measures strain on the exterior surface of a pipe to identify areas of wear on the interior surface of the pipe. The optical strain gauge system comprises an optical sensing interrogator and at least one optical fiber. The optical sensing interrogator comprises a light source and a light sensor. The at least one optical fiber includes fiber Bragg gratings along the length of the optical fiber. The optical fiber is arranged on the exterior surface of the pipe with the fiber Bragg gratings forming a two-dimensional array of points at which strain measurements are obtained. The two-dimensional array of strain measurement points provides an accurate assessment of the strains on the exterior of the pipe which can be used to identify areas of wear on the interior surface of the pipe.