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首页> 外文会议>ASME international conference on ocean, offshore and arctic engineering >ROOT CAUSE ANALYSIS OF BEND STIFFENER FAILURE DURING UMBILICAL FULL-SCALE FATIGUE TESTING
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ROOT CAUSE ANALYSIS OF BEND STIFFENER FAILURE DURING UMBILICAL FULL-SCALE FATIGUE TESTING

机译：脐带疲劳试验期间弯曲加强筋失效的根本原因分析

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Dynamic bend stiffeners are widely used to prevent overbending and achieve the desired fatigue life of umbilicals and flexible pipes by transferring bending moments locally to support structures on floaters. Full-scale fatigue testing of umbilical and bend stiffener assemblies has been historically used to verify umbilicals' fatigue performance in test lab conditions. Fatigue tests on steel tube umbilicals are usually conducted by testing the critical steel tube component to failure as detected by pressure drop and leakage. During a full-scale fatigue verification test conducted while executing a deep-water project in the Gulf of Mexico a bend stiffener has failed prior to failing the critical umbilical steel tube. This test failure, which is the first one encountered on projects stewarded by ExxonMobil Development Company (EMDC), manifested itself as inner and outer polyurethane (PU) cracks extending between 3 and 9 o'clock along the bend stiffener circumference at two different locations. A root cause analysis has been performed on the test failure based on the findings of the bend stiffener and umbilical dissections and temperature measurements. Two possible failure scenarios were constructed and investigated via finite element analyses (FEA), component adhesion tests, and thorough re-verification of manufacturing process and procedures. The FEA was instrumental in confirming adequate bend stiffener strength, and the likely failure scenario of PU fatigue failure due to overheating caused by high test-strain levels required to accelerate decades long operational loading into 3-month test loading. The FEA has been performed to bound the temperature distribution inside the bend stiffener based on loading conditions and temperature measurements taken during the test. Sequential structural-thermal analysis approach has been adopted by using quasi-static and steady state analyses. Equivalent strain distribution under fatigue loading was obtained through nonlinear structural analysis, and imported as heat source input in the PU material and the thermal model. Linear relationship between the strain rate and the heat generation rate has been used. The hysteretic heat generation model and heat transfer boundary conditions were calibrated by matching temperature results to thermocouple readings positioned at various locations on both the bend stiffener and umbilical during testing. The resulting temperature distributions showed the temperature at the inner crack had exceeded the temperature limit established via PU dogbone fatigue tests. Manufacturing process and procedures have been re-verified by conducting adhesion tests, quality checks and recoating of steel work. The root cause analysis has concluded that the bend stiffener design is fit for service. Three main development opportunities are suggested for industry's consideration to cover thermal design for operation and flex testing of bend stiffeners with umbilicals or flexible risers: a) testing methodology to establish PU heat generation with strain rate relationships, b) methodology and tools for coupled thermo-mechanical FEA, and c) non-destructive test methods for detection of coating and PU disbondments of finished products, and temperature measurement and profiling that can be used for FEA methodology and tool validation.
机译：动态弯曲加强件广泛用于通过在局部转移弯矩以支撑漂浮物上的结构来防止过度弯曲和实现脐带和柔性管的所需疲劳寿命。脐带和弯曲加强件组件的全规模疲劳测试已经历史上用于验证测试实验室条件中的脐带疲劳性能。钢管脐带上的疲劳试验通常通过将临界钢管部件测试到失效，例如通过压降和泄漏检测到的故障。在在墨西哥湾在执行深水项目的同时进行的全规模疲劳验证测试期间，在未临界脐带钢管之前弯曲加强件失效。这项试验失败，即埃克森美孚开发公司（EMDC）管辖的第一个遇到的第一个，表现为内部和外部聚氨酯（PU）裂缝在两个不同的位置处沿着弯曲加强圆周延伸3到9点之间。基于弯曲加强件和脐部剖析和温度测量的发现，对测试失败进行了根本原因分析。通过有限元分析（FEA），组分粘附试验和彻底重新验证制造工艺和程序来构建和研究两种可能的故障情景。 FEA是有助于确认足够的弯曲加强筋强度，并且由于高度测试 - 应变级别引起的高度过热而导致的PU疲劳失效的可能失效场景，以加速数十年的长期运行载荷为3个月的试验载荷。已经进行了FEA，以基于在测试期间采取的负载条件和温度测量结合弯曲加强件内的温度分布。通过使用准静态和稳态分析采用了顺序结构 - 热分析方法。通过非线性结构分析获得疲劳负载下的等效应变分布，并以PU材料和热模型进口为热源输入。已经使用应变率和发热速率之间的线性关系。通过将温度结果匹配在测试期间，通过将温度结果匹配温度读数，通过匹配温度读取的热电偶读数校准滞质发热模型和传热边界条件。所得到的温度分布显示内裂纹的温度超过了通过PU狗牛疲劳试验建立的温度极限。通过进行粘附测试，质量检查和钢化工作重新进行制造过程和程序已经重新验证。根本原因分析得出结论，弯曲加强件设计适合维修。建议为行业考虑进行三种主要发展机会，以涵盖脐带或柔性立管的弯曲加强筋的动作和弹性测试：a）测试方法，以应变率关系，b）用于耦合热量的方法和工具机械FEA和C）用于检测成品的涂层和PU分离的非破坏性测试方法，以及可用于FEA方法和工具验证的温度测量和分析。

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