Study On Status Inspection And Key Techniques For Safety Management Of Subsea Pipelines During Operation Period

Submarine pipelines are important infrastructures for offshore oil and gas development.However,they are also the weak link in the production and transportation of offshore oil and gas.Due to the challenges of the underwater environment,the submarine pipeline is inevitably affected by various risks during long-term operation,which causes the gradual decline in its operation safety,and even failure accidents such as leakage and fracture occurring in serious situations.Therefore,the safety management of submarine pipelines in operation is always one of the key problems of submarine pipeline engineering.At present,the safety management system for oil and gas pipelines is mainly established for urban pipelines.However,the structural characteristics and service environment between submarine pipelines and urban pipelines are quite different,which makes the safety management of submarine pipelines unique.In this paper,in view of the structure and service characteristics of submarine pipelines,the research focuses on the submarine pipeline safety management issue during the operational period.Based on the core process of safety management,the real-time status inspection and recognition,reliability assessment of corroded submarine pipeline and dynamic risk assessment and maintenance strategy optimization are researched in order to further improve the safety management system of submarine pipelines and provide a scientific basis for the safety management and application of practical engineering.The main contents and conclusions are summarized as follows:(1)Real-time status inspection method for in-service submarine pipelines.Due to the challenges of the underwater environment,the real-time status of submarine pipelines changes frequently showing great randomness and uncertainty.However,the real-time status inspection of submarine pipeline is the key and foundation for its safety management.Considering that conventional methods for inspecting submarine pipelines are inadequate,methods for real-time detection of submarine pipelines based on a Side-scan Sonar System(SSS),a Multi-beam Bathymetric System(MBS)and a Sub-bottom Profilers(SBP)that can function under these conditions are employed to resolve these shortfalls.In order to improve the inspection efficiency and reliability of test results,optimization of system parameters and method improvement are undertaken by analyzing the influence of system parameters on the test results.Furthermore,combined use of the SSS,MBS and SBP is adopted to comprehensively detect the status of submarine pipelines by considering the characteristics of each detection method.The feasibility of this method and the effectiveness of system parameter optimization design are verified through field tests,and the multi-source information of submarine pipelines is obtained which forms the complete three-dimensional information of submarine pipeline.(2)In-service status recognition and maintenance of submarine pipelineWhen the real-time detection results of submarine pipeline based on SSS,MBS and SBP are expressed in the form of 2D sonogram and bathymetric data,they are inefficient and unintuitive,not benefiting the status recognition of pipeline and the comprehensive management of detection results.Therefore,image analysis and 3D model reconstruction technology are used to integrate and process multi-source information of submarine pipelines.The characteristics and spatial coordinates of submarine pipelines are identified and extracted to construct 3D model of pipelines which realizes the 3D visualization and fine expression of inspection results.In addition,combined with the safety analysis of submarine pipeline structure,the 3D model is further used to conduct the quantitative safety assessment of submarine pipelines,with the pipeline shape parameters as the control parameters.Based on the assessment results,the risk identification and early warning are carried out,and the detection and maintenance method of submarine pipeline in operation period based on the state detection is proposed.(3)Damage prediction and safety assessment of corroded submarine pipelines.The randomness and polymorphism of corrosion damage and the uncertainty of corrosion model are the critical problems in safety assessment of submarine pipeline.Therefore,the cumulative evolution of corrosion state of submarine pipelines is researched using statistical analysis based on the corrosion data collection from the recycled subsea pipelines,and the optimal distribution models of the corrosion damage of submarine pipelines are determined.A Stochastic process corrosion growth model with multiple distributions is established to reduce the uncertainty of corrosion model selection.The method based on time series theory is put forward to modify and forecast the corrosion model by establishing ARIMA model,which reduces the uncertainty of the model parameters effectively.Furthermore,the model is used to identify and predict the corrosion state of submarine pipelines,and the structural reliability and life are evaluated and analyzed.(4)Dynamic reliability evaluation of corroded submarine pipelines.In practice,corrosion detection of submarine pipeline is more difficult and costly.This problem leads to a very limited test data available for structural reliability assessment.Therefore,the method based on Bayesian updating theory is proposed to update the model parameters with such imperfect inspection data.By constantly integrating new detection information into the corrosion growth model,the uncertainty of model selection and parameter estimation are reduced effectively.Combining the model with Bayesian updating theory,the residual strength degradation process is predicted.Furthermore,considering the multiple failure modes of submarine pipelines induced by corrosion,system reliability analysis theory and copula function are used to establish the reliability model to dynamic safety assessment and prediction in the presence of incomplete deterioration information.(5)Dynamic risk assessment of submarine pipeline system.Submarine pipeline system has the following characteristics: large scale,long service life and harsh service environment,which result in a strong dynamic risk and complex failure modes of submarine pipelines.It poses difficulty in the risk assessment.Therefore,based on risk identification,typical failure mode analysis(including static strength yield failure,corrosion induced leakage,burst,SCC and corrosion fatigue failure)and safety barrier analysis,a Bayesian Network(BN)model is established on the basis of the traditional Bow-tie(BT)model to describe the process of submarine pipeline failure accidents.By using this model,sensitivity analysis of risk factors and quantitative risk analysis for failure of submarine pipeline are conducted.It has revealed the critical events in the accident process.Furthermore,the dynamic risk assessment and prediction are conducted by introducing different types of evidence information into the BN model.It improves efficiency and management level of the safety management of the submarine pipelines and provides scientific basis for safety management strategy of submarine pipelines.(6)Long-term inspection and maintenance planning.The decision of inspection and maintenance of submarine pipeline is a critical issue of its safety assessment and safety management process.It is important to ensure structural integrity and long-term service continuity of submarine pipelines.Therefore,based on the reliability assessment and life cycle cost analysis,a model for long-term inspection and maintenance optimization is established.This model considers the noncomplete maintenance characteristic of the pipeline structure.The multi-objective genetic algorithm(GA)is used to solve the problem and conduct the cost sensitivity analysis.The result can be used to determine the long-term testing maintenance optimization scheme.In order to avoid and reduce the risk effectively,the resources configuration management can be optimized under the framework of decision-making and the inspection and maintenance planning can be implemented and improved continuously.