High precision is essential in the localization of anomalies (laminations, corrugations, corrosion, stress, blows, etc.) by the pig inspection device in any pipeline. The problem of distance measurement accuracy by an odometer inside a pipeline was investigated. The causes of error and the effect on error magnitude were surveyed. Odometer error can be caused by loss of the contact with the internal surface of the pipe. The effects of the odometer bumping into a weld or other mechanical defect in the pipe surface were investigated in detail. A special simulator of odometer wheel movement in a pipe was developed. Simulation of the odometer motion along the surface with joint welds was performed in gas and in fluids of different densities (water and oil) at six different speeds. The test results demonstrate that the distance measuring error of the odometer caused by joint welds depends on the travelling speed of the pig and can be as high as 10%.