Subsea pipeline spanning detection using a spherical detector with AC magnetic proximity switches

Spanning and bending of subsea pipelines seriously threatens pipeline transportation safety. Traditional external detection methods based on underwater robots of pipeline spanning have high costs and low detection efficiency; internal detection methods such as Pipeline Inspection Gauges (PIGs) have high blockage risk and can only provide very low frequent inspection. In order to facilitate and effectively detect subsea pipeline spanning, this paper proposes a spanning and bending pipeline inclination measurement based on in-pipe spherical detector (SD) and AC magnetic proximity switches (ACMPSes). It has the advantages of low blockage risk, high precision, low cost and being quasi real-time. Through off-line data processing, the pipeline inclination is calculated by using the tangential and normal accelerations when the ACMPS reaches the extreme point to determine the degree of pipeline spanning and bending. The operation circuit and SD of the ACMPSes are developed. Experiments are carried out in a 24 m long, 8 in. steel pipe that naturally downward bends. Results demonstrate that the SD can autonomously realize fixed-axis rolling driven by the water flow in the pipeline, and the repeated measurements under different flow velocities have high accuracy and good consistency. Within f2 degrees, the average error of single measurement is 0.14 degrees-0.31 degrees. After the fusion of multiple measurements, the maximum error is 0.21 degrees and the average error is 0.12 degrees, which proves the effectiveness and accuracy of this method.