Research On Crack Damage Identification Of Oil&Gas Pipeline Based On Piezoelectric Impedance Method

Piezoelectric impedance method, with high actuating frequency, not basing on any structure model, little influence on external environment and being sensitive to minor damage, which make it a promising and non-destructive evaluation method. Oil and gas pipeline under the external load and nature corrosion can lead to gradually damage, such as cracks, corrosion and perforation, which deduces the safety of the pipeline transportation, and results to leakage and explosion accident. Therefore, the damage identification research of oil and gas pipeline has become of quite significant to this area. The following research work of oil and gas pipeline with crack damage was carried out base on piezoelectric impedance method in this dissertation.(1) Using piezoelectric effect of piezoelectric material, based on basic performance parameters, on the basis of the research on existing piezoelectric equation, this paper established piezoelectric pipeline structure coupling model under considering the influence of the bonding layer, put forward electrical impedance equation, established the relation equation of the frequency and piezoelectric pipeline mechanical impedance based on the impedance expression.(2) An experiment research on damaged pipe had been conducted by piezoelectric impedance method. Pipe with single and multiple crack damage had been simulated by changing the thickness of pipe artificially. PZT impedance spectrum curve was measured under two kinds of boundary condition and eight damage states in this experiment. Result showed that the real component of the spectrum curve of PZT electrical impedance was significantly offset to the left and the peak of frequency was dropped once damage appears. The variation laws of spectrum curves could show whether the boundary conditions of pipe is changed. Through analyzing the experimental data, the indexes (the root mean square deviation and covariance) were obtained, which showed that RMSD and Cov can deduce the damage condition. Localization analysis on the pipeline crack damage can be achieved by piezoelectric impedance method based on sensors reasonable layout. According to the variation laws of the damage index and area, the quantifying mathematical model of pipeline damage degree was established, and quantitative assessment of pipeline crack damage can be realized in a certain extent. Furthermore, damage identification research of pipeline with multiple crack was carried out, based on the single crack damage, which showed that piezoelectric impedance method can effectively identify the damage of pipeline with single crack damage and multi-cracks. (3) By analyzing the damaged data of oil and gas pipe through probability statistical method and Gumbel extreme value distribution, the maximum crack depth of pipeline is calculated. Finally, the extremum model of the maximum crack depth of pipeline is given based on the quantifying mathematical model of pipeline damage degree, and the residual strength of pipeline with cracks was calculated according to the WES-2805Criterion.