Study On Signal Analysis And Defect Evaluation Of Offshore Pipeline Ultrasonic Defection Data

Offshore pipeline detection technology is one of the research hotspots in non-destructive testing field. The research on technologies, methods, and approaches for pipeline detection makes great theoretical and realistic sense. Based on"863"of the high technology research and development program"Offshore pipeline detection device and inspection technology", the research in this paper is focused on ultrasonic detection signal in order to detect the defects of offshore pipeline and evaluate the running condition of pipeline. The content of this paper is consisted of three parts: signal processing, flaw analysis and pipeline evaluation.In signal processing part, research on the de-noising method of ultrasonic signal and defect recognition algorithm was conducted. Firstly, Savitzky-Golay filter and empirical mode decomposition were combined to de-noise ultrasonic signal. The experiment showed that this method can effectively eliminate the white noise in each module and improve the signal-to-noise ratio of the reconstructed signal compared to existed method. Then linear prediction analysis was used to fit the envelope extracted by Hilbert transform of original signal. Different orders of linear prediction analysis were used to fit the envelope and the errors were compared to define the optimal linear prediction order. Lastly, defect recognition of linear prediction parameters was conducted by hidden Markov model. The experiment showed the recognition was up to 95%.In the offline analysis, it was consisted of signal processing and defect analysis. The offline analysis software was developed under Microsoft Visual Studio2003, using such techniques as MFC, mutli-thread, dynamic link library. The design pattern of the software was hierarchy in order to simply the development process. By processing original detection file, we can get A-scan signal file, defect's thickness file and defect's parameter file. These three files saved all the pipeline detection information through mutual relationship. The main function of offline analysis software includes the replay of ultrasonic echoes, the computation of pipeline thickness, the analysis of pipeline defect, the display of pipeline defect, the correction of pipeline thickness and the generation of detection report. The offline shortens the data processing period greatly and simplifies the data processing process.In the pipeline evaluation part, the gradation of defect and the estimation of pipeline's remain life were realized. To the defect computed by the offline analysis software, it could be graded by size. When the defect couldn't be graded by size, it could be classified by computing the maximal safe work pressure of pipeline. In order to assure the safety of the pipeline, multiple linear regression was introduced to estimate the remaining life of the pipeline. We can determine the variables closely related to the pipeline's life according to the existed pipeline detection data. Then we can get the regression equation of the pipeline's life. The remaining life of the pipeline could be computed by the multiple linear regression equation.Based on the research of ultrasonic signal processing approach and defect evaluation technology, this paper proposes a set of method to do offshore pipeline ultrasonic detection offline analysis including the de-noising method of ultrasonic signal, linear prediction method, defect recognition method and the method for estimation of pipeline's remaining life. This paper also realizes the development of offline analysis software and provides key technologies for offline analysis of ultrasonic signals.