基于可靠性方法的大口径天然气管段壁厚设计

Design of the wall thickness of a certain large diameter natural gas pipeline using a reliability method

我国陆上天然气管道规模庞大,管道路由地形、地貌和气候特征复杂多样。面对管道及管道所处环境的复杂性,提高油气管道的本质安全水平是行业和民众的共同需求,保证陆上天然气管道安全和可靠运行也越来越成为行业关注的焦点。为达到这个目标,可以采用从源头上对陆上天然气管道的设计方法进行改进的办法。目前天然气管道设计大多普遍利用传统的基于应力的设计方法,该方法由于采用单一的安全系数导致油气管道的安全裕度难以考量,针对此问题,基于可靠性的油气管道设计和评估方法(Reliability Based Design and Assessment,简称RBDA)正成为现代陆上天然气管道设计的趋向,该方法可量化管道全生命周期中的风险,避免采用不合理或过于保守的设计标准。故本研究综合CSAZ662《油气管道系统》标准规范的油气管道可靠性设计方法,并结合国内部分机构根据我国国情而修正的可靠性研究,利用RBDA方法流程,根据某段实际天然气管道确定该管道失效的主要原因(以腐蚀和第三方破坏为主),设计了管道在其生命周期内的极限状态,根据极限状态选择对应的极限状态方程类型,并利用多种数据统计分析方法和软件确定方程中所涉及各个随机变量参数的分布类型,之后利用蒙特卡洛法(Monte-Carlo法)计算设计壁厚条件下得到天然气管道失效概率,统筹考虑其他失效原因的权重,进而得到该管道的可靠度,将该可靠度数据与国内外标准规范确定的目标可靠度进行对比,检验是否满足可靠度目标。由此,对大口径天然气管段完成壁厚设计,实现了使用RBDA方法对1016 mm大口径天然气管道设计的整体流程。

The scale of onshore natural gas pipelines in China is huge,and the pipeline routes have complex and diverse terrain,landforms,and climate characteristics.Faced with the complexity of pipelines and the environment in which they operate,improving the intrinsic safety level of oil and gas pipelines is a common demand of the industry and the public.Ensuring the safe and reliable operation of onshore natural gas pipelines has become an increasingly important focus of industry attention.To achieve this goal,it is possible to improve the design method of onshore natural gas pipelines from the source.At present,traditional stress based design methods are widely used in natural gas pipeline design.Due to the use of a single safety factor,it is difficult to consider the safety margin of oil and gas pipelines.To address this issue,Reliability Based Design and Assessment(RBDA)is becoming a trend in modern onshore natural gas pipeline design.This method can quantify the risks throughout the entire life cycle of the pipeline and avoid using unreasonable or overly conservative design standards.Therefore,this study integrates the reliability design method of the CSA Z662"Oil and Gas Pipeline System"standard specification for oil and gas pipelines,and combines it with the reliability research revised by some domestic institutions according to China's national conditions.Using the RBDA method process,the main causes of pipeline failure(mainly corrosion and third-party damage)are determined based on a certain section of actual natural gas pipeline.The limit state of the pipeline is designed during its life cycle,and the corresponding limit state equation type is selected based on the limit state.Multiple data statistical analysis methods and software are used to determine the distribution types of various random variable parameters involved in the equation.Then,the Monte Carlo method is used to calculate the failure prob-ability of the natural gas pipeline under the design wall thickness condition,and the weights of other failure causes are considered comprehensively to obtain the natural gas pipeline failure probability.The reliability of the pipeline,Compare the reliability data with the target reliability determined by domestic and foreign standard specifications to verify whether it meets the reliability target.Thus,the wall thickness design of the large-diameter natural gas pipeline section was completed,realizing the overall process of using RBDA method for the design of 1016mm large-diameter natural gas pipelines.