Dynamic Safety Evaluation Method For The Long-distance Pipeline Corrosion Protection System

Due to the serious damage of the long-distance pipeline accidents,it is more and more important for the related safety management and maintenance,the pipeline corrosion protection is the key component of the long-distance pipeline integrity management,and safety evaluation of the system is also the basis and important part of the pipeline integrity management.Nowdays,it is a preliminary stage for the evaluation method based on the objective data analysis and data fusion in domestic.In addition,because of the dynamic characteristics of the system,and the limitations of the static evaluation method,the related evaluation methods reveal some drawbacks such as high subjectivity,poor timeliness,and weak adaptability and effectiveness.Therefore,based on the fusion and analysis of the objective detection data,this thesis studies the safety classification evaluation,the comprehensive evaluation,and the dynamic safety evaluation method as well as theory application of the pipeline corrosion protection system.The research is effective to implement safety evaluation and integrity management decisions for the pipeline corrosion protection system.The paper studies the classification and mechanism of corrosion,as well as the related analysis method of the electrochemical corrosion,combined with the long distance pipeline corrosion factors analysis,establishes the failure accident tree of the long-distance pipeline corrosion protection,which provides the standard basis for the constructing evaluation index system of the long distance pipeline corrosion protection system.According to the specific characteristics of the long-distance pipeline external corrosion,combining with the field measurement,the physical and chemical properties,and the test data analysis,the research studies the soil corrosion,stray current corrosion,cathodic protection,and the weight of anticorrosive layer protection,as well as the security classification and dynamic evaluation.In the past evaluation of the soil corrosion grade,the prominent influence factors vary according to different methods of soil the corrosion grade evaluation.It is considered inadequately for the adaptability and effectiveness of the method in different regional condition,resulting in low reliability and the poor efficiency.According to the above problems and the dynamic characteristics of multiple factors and different influence in different geographical conditions,also the test data with redundancy and abnormality,this study prososes dynamic evaluation of soil corrosion level using the rough set-decision tree-support vector machine(RS-DT-SVM)combination method.From the evaluation test effect of the loam area,the RS-DT-SVM has the relative superiority in the evaluation grade analysis of the multi-factor control system.According to the stray current corrosion principle,the Laplace's equation is used to establish the stray current corrosion state mathematical model.Based on this model,this study implements the experiment research using the Comsol finite element,it verifies the relationship that the stray current is inversely proportional to the soil resistivity and proportional to the pipe-to-soil potential,which provides the corresponding theoretical basis for the stray current corrosion strength evaluation.With the relevant standards at home and abroad,this thesis points out the relationship between this theoretical basis and the soil potential gradient,and the tube position offset,alone with the evaluation index extent.For the cathodic protection evaluation,we use the cathodic protection criteria as indirect measurement method for the effectiveness evaluation,the determination method of the average IR drop calculation of the cathodic protection system is proposed,which is simpler than the existing average IR drop measure method,at the same time,utilizing this average IR drop and the tested electric potential of each section pipeline test pile,it could estimate whether the pipeline actual electric potential is in accord with the rule of the cathodic protection or not,it provides the basis for the pipeline integrity management and the cathodic protection system evaluation.For the anticorrosive layer protection evaluation,according to the study considered with different anticorrosive coatings using different test methods at home and abroad,and in accordance with the relevant standards and guidelines,we get the classification index system and evaluation method of the corrosion protection layer in the excavation and trenchless case.Then regarding to the limitation and insufficiency of the static evaluation method,this thesis considers the dynamic safety evaluation of the coating degradation trend,on this basis,it studies and constructs the dynamic safety evaluation method of the anticorrosive layer outside integrating the set pair(SPA)state evaluation and the Markov chain trend analysis.The method is verified by validation examples;thereby it can make a dynamic and effective analysis for the safety level of the anticorrosive coating,and assess the changed safety effectiveness grade of the anticorrosive coating after period of time,which improves the dynamic evaluation ability of the pipeline anticorrosion coating degradation trend,and provides a decision-making theory evidence for the pipeline maintenance.For the study of the grading evaluation method,in order to reduce the subjective factors and increase the pertinence of the objective factors analysis,combining with the characteristics of each index factor,for the evaluation index weight coefficient,this thesie presents the utilization of the actual and objective test data,and make the two methods into calculation and verification of weight combination based on the analysis characteristics of the rough set and entropy calculation method,then obtain the determination of the weight value again by the comprehensive average,so as to determine the weight value by the comprehensive average value.Thus it could improve the applicability and reliability of the entropy calculation method.Then by using the set pair theory clustering analysis method and the characteristics of each index factor,the targeted connection degree application model for classification evaluation could be established,which improves the applicability of the classification evaluation and provides the application guidance for the weight analysis of the evaluation index system.Aiming at the existing problem of the comprehensive evaluation method of the long distance transmission pipeline,the research proposes an analysis ideas of the set pair theory using the multivariate connection number,and makes the corrosion and protection index system and the evaluation level into a set,then according to the index characteristics to establish the targeted four element connection degree formula of the corrosion and protection situation,which can consider the connection between the indicators,and achieve the comprehensive evaluation on situational and protective corrosion situation on the two aspects of contact,and reflect the corrosion and protection grade of each section to find out the key area of the corrosion protection.At the same time,it can also comprehensively grasp the dangerous level of the pipeline corrosion and protection situation,and improve the applicability and rationality of the evaluation.In order to describe properly the dynamic characteristics of the system,using the partial connection number of the set pair theory,the pipeline corrosion as well as the advantages and disadvantages of the protection trends are evaluated dynamicly,the dynamic evaluation method of the pipeline corrosion and protection is proposed,these play a significance of comprehensive evaluation and supply an application guide to the safety evaluation of the pipeline corrosion protection system.Based on the actual testing soil corrosion data of 48 groups,the pipeline corrosion protection system integrated data of 6 groups,a total of 54 groups,and selects two one-level index factors,four secondary index factors,20 three-level index factors,The above approach implements the evaluation method,the result verifies the practicability and validity of the evaluation method,which proves the research achievements by applying the safety evaluation method of the thesis,and makes the dynamic and adaptability evaluation of the system safety performance according to the characteristics of the actual environment,it has important significance on the safety research of the long-distance pipeline corrosion protection system.