With the continuous increase of offshore oil and gas exploitation activities, the number of subsea pipelines is becoming larger and larger, which leads to frequent occurrence of subsea pipeline accidents. Long-term safe operation of subsea pipelines can be ensured by regular defect detection. The premise of locating and disposing defects is to accurately measure the geographic coordinates of subsea pipelines. Our research group has put forward a kind of pipeline spherical internal detector (SD), which has the advantages of convenient implementation, low risk to jam. For the SD, this paper has carried out research on the key technology of precise measurement of subsea pipelines’ geographic coordinates using the internal magnetic fields. The main work is as follows:
(1) Magnetic tensor invariant calibration method for magnetometer array has been studied and L-M algorithm is taken to solve the parameters, which is efficient and accurate. Field calibration experiment has proved this method is effective and has good robustness.
(2) A new method of measuring pipeline’s pitch angle is proposed. Under the experimental condition of using AC servo motor to drive the sensor instead of the SD to rotate, the pitch angle measurement error is less than 0.2°.
(3) Magnetic anomaly of spiral weld and buckling pipeline are used as new mark points to calibrate the geographic coordinates of subsea pipelines. Experimental results show that the newly designed SD can successfully identify spiral welds and buckling pipeline.