海底管道遭受船锚撞击的风险分析

Risk Analysis of Submarine Pipeline Subjected to Impact Loads by Anchor

坠锚事故容易对海底管道造成撞击损伤,引起环境污染及经济损失。为保证管道在运行期间的安全,有必要对其进行风险分析。基于可靠度理论,在DNV规范(DNV-RP-F107)推荐方法的基础上,本文提出了一种失效概率的计算方法,该方法可考虑船锚质量、尺寸及管道尺寸、材料强度等因素对失效概率的影响,与实际情况更相符。结合工程实例,对船锚撞击作用下的海底管道进行了风险分析。考虑随机变量的变异性,探讨了管道失效概率对各变量的敏感性。分析结果可为降低海底管道损伤风险及采取合理的防护措施提供技术参考。

As the main medium of transportation of oil and gas,submarine pipeline has many features,such as fast and economy.How to ensuring the safety during the operation period is the key to explore the marine oil and gas resources smoothly.Recently,with the increase of humankind’s activities on the ocean,it is inevitable that anchors will drop into the sea due to operating errors,which may lead to failure of the pipelines once impact on them.The failure of pipelines may cause great financial losses and serious environment pollution.So in order to lower the risk and provide scientific basis for protection it is necessary to do the reliability and risk analysis of pipelines.Previous research on the risk analysis of pipelines,the methods used to calculate the failure probability are mostly based on the DNV-RP-F107 recommended method(hereinafter referred to as DNV method),which barely takes the variation of the anchor’size and mass into consideration when the anchors are divided into the same category according to DNV-RP-F107 and is insensitive to the variation of pipeline size and material.Therefore,it is not correspondent with practice and may cause errors during the risk analysis of pipelines.To solve the above problems,this paper proposes a method based on reliability theory to calculate the failure probability which can take the above influence factors into consideration,compared with DNV method.With this method,the calculation of the failure probability includes two steps:Firstly,determine the impact probability.Secondly,according to the DNV related standards and the method to calculate the pipeline deformation,the implicit limit state equation can be established and solved,then the results solved can be converted to the failure probability under certain impact energy.Finally,the failure probability is the product of the results from the two steps.Taking the practical project for examples,the analysis of the influence of various factors on the failure probability of pipeline are done in this paper,including the mass of anchor,the material and size of pipeline and distance from the place where the anchor dropped.Meanwhile,considering the variability of stochastic variables,the sensitivity of stochastic variables to the failure probability is discussed.The results show that:For the influence of anchor mass,the method proposed can take it into consideration.With the increase of the anchor mass,the failure probability increases,and the risk rank rise to level2 form level1.However,the results calculated by DNV method remain the same when the anchor mass changes,which does not match with the actual situation.For the influence of pipeline material and size,the failure probability calculated by the proposed method varies when the above variables change.Whereas,results calculated by DNV method are almost constant,which cannot reflect the influence of pipeline material and size.For the influence of the distance from the dropped point,the failure probabilities of pipeline segment in areas with different distances from the dropped point differ.Within a relatively short distance,the failure probability increases with the distance increases till it reaches the maximum in the area of around 70~80 meters away from the dropped point,after where it decreases continuously with the increase of the distance.And for the sensitive analysis of stochastic variables to failure probability,the greatest influence factor is the collapsing strength of concrete,then are the wall thickness and the outer diameter of pipeline,the least is the yield strength of pipeline.Therefore,enhancing strength of concrete can lower the risk of the pipeline damage when the pipeline size and material are unable to change due to some restrictions.In conclusion,compared with DNV method,the method proposed can take more influence factors into consideration,which is in consistent with the actual situation and more reasonable.And the analysis results can provide scientific basis and theoretical guidance for the design and protection of pipeline.