SUBSEA FREE SPAN PIPELINE DAMAGE DETECTION BASED ON WAVELET TRANSFORM UNDER ENVIRONMENTAL LOAD

During their service life, marine pipelines continually accumulate damage as a result of the action of various environmental forces. Clearly the development of robust techniques for earlydamage detection is very important to avoid the possible occurrence of a disastrous structural failure. Most of vibration-based damage detection methods require the modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such a good sensitive indication of structural damage. In this paper, structural damage is identified based on a new method called Detail Signal Energy Rate Index (DSERI). Damage localization of offshorepipeline is then based on Continuous Wavelet Transform (CWT) and Discrete Wavelet Transform (DWT). For modeling the damage, the stiffness of 1 and 2 elements are reduced in three models and the dynamic signals are measured by finite element analysis. The dynamicsignals are analyzed by applying discrete and continuous wavelet transforms. Then by using Daubechies wavelet, a peak is clearly evident and the exact damage location is identified by thepeak with the maximum absolute value in the plots of the detail signal calculated with the DWTand CWT. To eliminate the effects of the boundary conditions on the wavelet-based damage, the authors proposed a new method: DSERI. Component energies are then calculated and used for damage assessment. The results show that the DSERI are good candidate indices that aresensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and location of damage. Wavelet coefficient is a good candidate for structural damage identification when damage occurs at the middle of pipeline but not sensitive for damaged elements near to supports.

Keywords:

free span pipeline , damage detection , wavelet transform