Submarine Pipeline Risk Assessment In View Of Marine Environmental Factors

In order to transport the oil and gas from sea to land, the common mode of transport is to lay a submarine pipeline directly between the production site and the destination point. Offshore oil and gas feedstock transport based on submarine pipeline safe operation, however, many years of operation of the submarine pipeline gradually into the pipeline rupture, failure and other frequent stages of the accident, not only caused direct economic losses and even serious damage to the marine environment, caused strong social repercussions. Therefore, in order to control of submarine pipeline accident, reduce the accident rate, the weak link of the capture pipeline supervision, from economics from risk assessment method, controls the risk factors in the management of admissible risk within the scope, carry out for in pipe system of risk assessment research.Based on the summary of domestic and oversea pipeline risk assessment under the premise of the research scholars, to our country GBT24353-2009 "risk management principles and implementation guidelines for the risk assessment of technical support, to introduce the basic theory of risk assessment, basic steps and different kinds of evaluation methods, for the pipeline by the influence of marine environment factors and selection of appropriate assessment methods, assessment model was set up and build a reasonable evaluation index system, determine the grading standards, and the use of the system, attempts to our country’s existing submarine pipeline risk assessment.This article briefly outline four aspects from the seafloor topography and geomorphology, seabed types, the hydrodynamic environment and typical marine disasters in divided area. After the overview of the environment of China’s four major ocean regions, we can see that, effects of safety of submarine pipeline of marine environment is divided into two major categories of geological environment and marine meteorological and hydrological environment, which in-depth discussion of pipeline in the geological environment consists of sand waves and sand ridges, sand liquefaction, landslide, shallow gas, buried ancient Valley and undersea earthquake; meteorological and oceanographic environment consists of ice, tide and tidal current, typhoon, waves.To recommend and introduce the fault tree analysis method, application of fault tree analysis of the reliability and safety of the technical principle, identify the risk of submarine pipeline system in marine environmental factors, choose to submarine pipeline rupture as top event of fault tree analysis model, and on this basis, the pipeline quantitative risk analysis based on fault tree model is constructed. The fault tree model of submarine pipeline, which is based on the marine environment factors, has the characteristics of qualitative and quantitative analysis, which provides the basis for further quantitative calculation.In natural science, to mathematically describe things accuracy and precision has been pursued by the people. However, in real life, there is a many fuzzy phenomena makes precise mathematical model has little may be solved, especially running in the marine oil and gas pipeline system than on land is more complex, this system also exist many unknown information and known information, the introduction of grey fuzzy recognition theory, according to the characteristics of the marine environment "part of the known information, partial information unknown" fuzzy, uncertainty, put forward a according to the marine environment factors of submarine pipeline gray fuzzy evaluation model.After the model is determined, the gray fuzzy evaluation of the submarine pipeline of Pinghu oil and gas field in the East China Sea is attempted, and the characteristics of the marine environment in the East China Sea area are determined. Assessment process will be in the pipeline is divided into four regions, to avoid the whole section of the pipeline together evaluation leads to the equalization of information, causes to obtain the evaluation results generalize, so we can’t get inside a pipe segment of the risk. After calculated from seabed pipeline of Pinghu oil and gas field development fuzzy evaluation and rupture of the frequency estimates.Pipeline detection data:taking into account the work of pipeline backfill implementation, the dew state of the pipeline is sort of P2>P1>P4>P3, the pipeline critical floating state sort is P2>P1>P4>P3, the pipeline floating state sort is P2=P1 P4>P3.Fuzzy evaluation:in the minimum gray Department confidence degree and modulus maximum membership degree principle, obtained the evaluation results, the P1 (Pinghu oil and gas pipeline) partition be subordinate to belongs to grade I risk (0.351 for the maximum degree of membership). That is to say is in a safe condition; 0.330 belonging to the P2 partition is grade II risk, is relatively safe system; 0.386 maximum membership degree that P3 partition is grade I risk, that is to the security of the system; 0.51 maximum membership degree of P4 partition is grade I risk, is the security of the system, the overall ranking for P2>P1>P4>P3.Rupture frequency estimates:after the estimate, the rupture frequency of the P1 partition is estimated as fP1=0.007(/a); the rupture frequency of the P2 partition is estimated as fP2=0.016(/a); the rupture frequency of the P3 partition is estimated as fP3=0.012(/a); the rupture frequency of the P4 partition is estimated as fP4= 0.011 (/a); and the conclusion is drawn that the partition of rupture frequencies from high to low order for P2>P3>P4>P1.We compare the values of detection data, fuzzy evaluation and rupture frequency, you can get the most risk of submarine pipelines in the P2 District, it needs strengthen inspections and maintenance.