Multiaxial Fatigue Analysis on Reeled Deepwater Steel Catenary Risers with Girth Weld Defects

In the present study, we simulated the reel-lay installation process of deepwater steel catenary risers（SCRs） using the finite element method and proposed multiaxial fatigue analysis for reeled SCRs. The reel-lay method is one of the most efficient and economical pipeline installation methods. However, material properties of reeled risers may change, especially in the weld zone, which can affect the fatigue performance. Applying finite element analysis（FEA）, we simulated an installation load history through the reel, aligner, and straightener and analyzed the property variations. The impact of weld defects during the installation process, lack of penetration and lack of fusion, was also discussed. Based on the FEA results, we used the Brown-Miller criterion combined with the critical plane approach to predict the fatigue life of reeled and non-reeled models. The results indicated that a weld defect has a significant influence on the material properties of a riser, and the reel-lay method can significantly reduce the fatigue life of SCRs. The analysis conclusion can help designers understand the mechanical performance of welds during reel-lay installation.     

基于有限元分析的卷管法管道安装实时研究

采用卷管法铺设管道时,管道和铺设设备之间的接触作用十分复杂,并且管道在弯曲过程中将会产生塑性变形并可能发生局部屈曲,导致管道失效。基于有限元模型(FEM)实时模拟卷管法安装的整个过程,研究管道与铺设设备之间的接触作用;分析管道对于环境载荷和船体运动的动态响应;获得管道的应力应变值以校核局部屈曲。研究结果表明,管道弯矩大部分来源于管道与安装设备间的接触作用,而环境载荷及船体运动对管道的弯曲应力影响较小。     

Multiaxial Fatigue Analysis on Reeled Deepwater Steel Catenary Risers with Girth Weld Defects

In the present study, we simulated the reel-lay installation process of deepwater steel catenary risers (SCRs) using the finite element method and proposed multiaxial fatigue analysis for reeled SCRs. The reel-lay method is one of the most efficient and economical pipeline installation methods. However, material properties of reeled risers may change, especially in the weld zone, which can affect the fatigue performance. Applying finite element analysis (FEA), we simulated an installation load history through the reel, aligner, and straightener and analyzed the property variations. The impact of weld defects during the installation process, lack of penetration and lack of fusion, was also discussed. Based on the FEA results, we used the Brown-Miller criterion combined with the critical plane approach to predict the fatigue life of reeled and non-reeled models. The results indicated that a weld defect has a significant influence on the material properties of a riser, and the reel-lay method can significantly reduce the fatigue life of SCRs. The analysis conclusion can help designers understand the mechanical performance of welds during reel-lay installation.     

基于ABAQUS的卷管式铺管法管道变形敏感性分析

卷管式铺管法在海管铺设中的应用愈发广泛,在铺设作业中管道会发生几何非线性变形,导致出现复杂的力学性能变化。针对管道在上卷、退卷过程中的屈服变化过程,通过弹塑性理论进行分析,推导出管道退卷后残余轴向应力的解析解;随后利用有限元软件ABAQUS建立模型实例,对比解析解与有限元模型,两者的计算结果基本吻合。基于上述有限元模型,研究上卷时的张力和退卷时的后张力对椭圆度、截面轴向应力和剪切应力的影响,并进行敏感性分析。模拟结果表明张力和后张力变化会影响管道截面的变形程度,退卷后截面上残余的轴向应力远高于剪切应力,并且通过敏感性分析,得到了残余椭圆度、残余应力随张力和后张力变化的规律。研究可为卷管铺设过程中张力和后张力的选择提供参考和借鉴。     

柔性管卷管式铺管上卷有限元模拟

采用卷管法进行海底管道铺设过程中,管道首先通过牵引作用上卷于卷筒进行储存。管道与卷筒发生非线性接触,可能会产生复杂的塑性变形和局部屈曲。通过全尺寸柔性管力学性能试验获得柔性管轴力—应变以及弯曲—曲率等非线性力学性能关系,将试验所得的非线性材料性能参数导入建立的两种柔性管上卷ABAQUS有限元模型（梁—实体单元模型与壳和桁架—实体单元模型）,实现柔性管较大轴向抗拉刚度和较小抗弯刚度的同步模拟以及管道与卷筒的非线性接触响应特征。通过对比分析两种有限元模型数值模拟得到的管道弯矩、弯曲曲率、管道轴力、管道与卷筒的接触压强等数据,发现在管道上卷过程中管道沿副法线方向的SM3弯矩占据其弯曲变形主导地位;管道与卷筒之间的摩擦效应对于管道轴力的影响较为显著;管道与卷筒的最大接触压强主要发生在卷管过渡段区域。     

焊接所致力学性能不均匀性对卷管法安装管道完整性影响

管道由于热加工影响,其焊缝处及邻域的热影响区管段材料性能将与其余管段存在差异,即管道存在力学性能不均匀性。分别采用各向同性硬化材料模型与Ramberg-Osgood材料模型,应用ABAQUS仿真模拟卷管过程,并对仿真结果进行对比,表明使用Ramberg-Osgood材料模型能够更真实地模拟管道的力学行为,获得更接近真实值的管道力学响应。基于此模型采用控制度量法研究力学性能不均匀性的影响。研究表明:管道力学性能不均匀性水平越高,对管道结构完整性造成的不良影响也越大。     

基于悬臂梁模型的管道矫直理论及有限元分析

海底管道的卷管铺设过程涉及多次正向和反向弯曲,并会产生较大的塑性变形。在铺设入水前,管道必须进行矫直处理,因此如何准确预测矫直过程中管道的力学响应以及如何对矫直器进行合理的设置具有重要意义。针对中国首艘卷管式铺管船“深达号”的矫直装置设计与典型工况,建立了一种基于悬臂梁的力学理论模型。该模型综合考虑了铺设过程中退卷和矫直的加载历程、管道材料的弹塑性特性以及校准器和上、下矫直器的相对位置关系。模型能实现对反弯半径及矫直器姿态等关键参数的计算。建立有限元分析模型,对理论模型进行验证并对管道矫直过程进行数值分析。结果表明理论模型可以准确预测管道矫直所需反弯半径、矫直器侧向行程以及倾角等参数。在管道矫直过程中,上矫直器处的作用载荷远大于下矫直器处。所提出的矫直理论模型可适用于不同尺寸管道的矫直分析,矫直后残余曲率满足DNV规范要求,预期可为“深达号”的实际矫直工艺设计提供指导。     

卷管铺设的海管曲率模型及残余应力计算

弯曲曲率是使用卷管铺设时首要控制的参数之一。通过对海管的上卷加载、完全卸载、退卷加载及再次卸载等过程的弹塑性分析,建立了各个阶段的曲率模型,并推导了海管完全卸载时残余应力的解析解。在此基础上,分析了曲率、曲率比、残余曲率比及残余应力等参数的影响因素,得到了卷管铺设中海管的最优弯曲曲率及海管截面上的残余应力分布规律,并提出了基于弹塑性理论的海管的残余曲率及残余应力的控制建议。