Pipeline Health Monitoring Based On Optical Fiber Strain Sensing Technology

Underground pipelines constitute one of the most important ways to transport large amounts of oil and gas through long distances.Long-distance pipelines,especially the buried pipelines,have inevitably crossed through complex geological environment,which always suffer from natural or man-made disasters.These factors may lead to damage,which always cause major accidents.Therefore,it is of great significance to monitor the safety of pipeline in real time.This dissertation presents pipeline health monitoring method based on optical fiber sensing technology.The following are the main studies in this dissertation.In the first chapter,the development status of the pipeline transportation industry was introduced.The main threats to pipeline safety are corrosion,leakage and large deformation.By summarizing the advantages and disadvantages of the current pipeline detection and monitoring approaches proposed by domestic and foreign experts,especially for the optical fiber sensing based methods,this paper proposed pipeline health monitoring method based on Optical Frequency Domain Reflection(OFDR)technology and fiber Bragg grating sensing technology.A pipeline internal corrosion monitoring method based on hoop strain field was proposed in the second chapter.For theoretical analysis,the relationship between hoop strain and wall thickness was studied based on elastic mechanics principle.To investigate the distribution characteristics of the hoop strain field caused by uniform corrosion and local corrosion,finit element method analysis were carried out by Abaqus software.According to the distribution of hoop strain field caused by internal corrosion,a strain field sensor net was invented to measure the hoop strain distribution and to reconstruct the hoop strain field.Through the strain field,internal corrosion can be monitored accurately and intuitively.Combined with the pipeline safety evaluation criterion,the corrosion safety evaluation method was proposed.In the third chapter,a series of tests were conducted to verify the pipeline corrosion monitoring method.In these tests,different types of corrosion were simulated by different internal defect angles and defect depths,and the hoop strain distribution around the pipeline cross section was measured by OFDR technolofy.Test results demonstrated that the internal corrosion can be effectively monitored by OFDR technology.In order to verify whether the strain field sensor net can be used to monitor the pipeline internal corrosion process,a real-time monitoring test of the pipeline internal corrosion process was carried out.The test proved that the internal local corrosion can be effectively located and evaluated by the strain field sensor net.In the fourth chapter,we proposed a method of pipeline leakage location and a linear fitting method to identify the knee point of negative pressure wave respectively.Based on the relationship between hoop strain and internal pressure of the pipeline,this dissertation proposed a method to monitor the leakage of the pipeline by hoop strain.Combined with the advantages of fiber Bragg gratling(FBG)sensing,a method for locating pipeline leakage through FBG sensor array was proposed.The negative pressure wave velocity is not needed in the algorithm of leakage location.In order to calculate the occurance time of the knee point,the characteristics of the hoop strain caused by negative pressure wave was investigated.Based on the characteristics,a linear fitting method was proposed to locate the knee point of the negative pressure wave.To verify these two proposed methods,pipeline leakage tests were carried out and proved that leakage location can be located effectively..Pipelines in permafrost and seasonally frozen soil areas will have large deformation which will threaten the safety of pipeline.In the fifth chapter,a pipeline deformation monitoring approach was investigated,especially for the pipeline deformation caused by frozen soil in cold regions.In this approach,OFDR technology is used to measure the distributed axial strain,the tangential angle recursive algorithm is used to reconstruct the shape of the pipeline.To study whether this method is suitable for practical engineering,a simulation test was carried out.In the test,the pipeline model was deformed due to the frost heaving force.Based on the OFDR technology,the axial strain distribution of the pipeline model was measured,and the shape of the pipeline model was reconstructed.The results indicated that OFDR technology provides an effective way to monitor pipeline deformation in cold areas.The sixth chapter is the summary of this article and the prospects for future research work.