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The problem of estimation with high accuracy the location of the pipeline defects arises during the regular pipeline inspection. The in-line inspection tool (robot, pig) equipped with navigation system. Modern requirements for the accuracy of a navigation solutions lie within 1-4 m. Navigation system of the robot comprises: - Inertial Measurement Unit (IMU) or staprapdown inertrial navigation system (INS) that includes angular rate sensors (ARS) -- gyroscopes and accelerometers. Fiber optic gyros of medium level of accuracy usually are used. - Odometer wheels. - Data acquisition and storage system. DGPS-derived coordinates of the markers are also used as an aiding position data. Typical distance between adjacent markers is 1km and bigger. The integrated navigation model has to consider the following factors: - Instrument error of the inertial sensors; - Scale factor of the odometer; - Possible misalignment between IMU longitudial axis and "measuring"\ axis of the odometer; - Displacement between odometer wheel and the center of INS. In the paper, the methodical aspects for the elaboration of INS-odometer-markers integration algorithms are discussed. The developed technique of data fusion is not related to the concrete technical specifications of inertial sensors and therefore is rather universal. Navigation tests were done by three companies, related with oil and gas pipelines inspection. These companies use inertial sensors from different suppliers and they have used post-processing software elaborated by MSU laboratory of navigation and control. The multiple results of data post-processing showed that the desired accuracy of 1-4 m is achievable.