Vibration Detection of Spanning Subsea Pipelines by Using a Spherical Detector

This paper proposes a method for detecting the vibration of subsea spanning pipelines by using a spherical detector (SD) equipped with a triaxial accelerometer. The mathematical analyses and experiments demonstrate that the acceleration modulus square (AMS) and the AMS of the ac components (AMS_AC) of the acceleration signals recorded by the SD have one characteristic component whose frequency is equal to and can be used to determine the pipeline vibration frequency. As the amplitude of this component is immune to the rotation noises of the SD, its signal-to-noise ratio is higher than that of other components whose frequencies are the mixture of the vibration and rotation frequencies. Removing the dc bias along the three sensitive axes can eliminate other characteristic frequencies to make the AMS_AC having the unique frequency to indicate the pipeline vibration. The vibration frequency can be accurately and sensitively identified by using the AMS_AC. The detection thresholds of 5-, 10-, and 15-Hz vibrations are 0.6, 0.4, and 0.2 mm with regard to the amplitude, respectively.