Study On Optimization Of Subsea Pipeline Design Based On Assessment Of Oil Spill Risk

Subsea pipeline is usually subjected to complex load during service.Once pipeline leak happens,it will easily cause sea pollution to ecological environment and coastline since it is difficult to grasp the locomotion trajectory of spilled oil in time.Therefore,in subsea pipeline design,the reliability should be totally considered,whereas leading to additional construction investment of pipeline.Based on this,there is a problem of how to improve the subsea pipeline economy under the prerequisite for a reliable running state of pipeline pretty much to be solved.In this paper,an optimization approach to subsea pipeline design based on assessment of oil spill risk is proposed,aiming to work out the optimal pipeline design program.Firstly,the assessment model of oil spill risk of subsea pipeline is established,regarding five factors,namely,quantity of spilled oil,oil spill location,oil property,environmental condition of sea and management and emergency,as assessment index.Next,supposing there is a pipeline leak accident resulting in oil spill,it is required to implement a risk assessment.Markov chain Monte Carlo(MCMC)is applied to obtaining stochastic values of leak location and leak volume,and these parameters are combined into the established transient hydraulic model of pipeline in order to solve the accurate location and volume.According to the known leak volume and surrounding environment of pipeline,the assessment model of oil spill risk of subsea pipeline can be solved to get the risk grade of this accident.Finally,the optimization model of parameter design for subsea pipeline is set up,which sets the minimum pipeline construction and running costs as the objective function with the decision variables of inner diameter,wall thickness,insulation thickness,and temperature and pressure at start point.The reliability analysis of pipeline hydrothermal and structural is included.And one proper optimization algorithm is determined for model solving.From the model application in case study,the grade of oil spill pollution caused by subsea pipeline leak is severe,and thus,pipeline failure should be avoided in pipeline design.Four improved PSOs are tested,and the Monte Carlo-coupled multi-swarm self-learning PSO(MC-SLPSO)with superior calculating capacity is determined to solve the model.The obtained optimal design program is as follows: inner diameter of 218 mm,wall thickness of 8mm,no insulation,multi-phase pump required at start point to boost pressure by 2.9MPa,2.9MPa,2.7MPa,2.3MPa per year.